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常用的数据库有三大类，MySQL,MongoDB和 Redis。Python对这三大数据库都有很好的支持。其中我个人比较喜欢Mongodb，简单快捷，操作方便。下面这篇文章对Mongodb常用的增删改查的操作，总结的非常到位。这篇是来自大名鼎鼎的爬虫大神崔庆才老师，我和他聊过几次，相谈甚欢，有一种相见恨晚的赶脚。崔老师的技术非常牛，欢迎关注他的，进击的Coder。
MongoDB是由C++语言编写的非关系型数据库，是一个基于分布式文件存储的开源数据库系统，其内容存储形式类似JSON对象，它的字段值可以包含其他文档、数组及文档数组，非常灵活。在这一节中，我们就来看看Python 3下MongoDB的存储操作。
1.准备工作
在开始之前，请确保已经安装好了MongoDB并启动了其服务，并且安装好了Python的PyMongo库。
连接MongoDB时，我们需要使用PyMongo库里面的MongoClient。一般来说，传入MongoDB的IP及端口即可，其中第一个参数为地址host，第二个参数为端口port（如果不给它传递参数，默认是27017）：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;"><span class="" style="font-size: 15px;max-width: 100%;font-weight: bold;box-sizing: border-box !important;word-wrap: break-word !important;">import</span> pymongo<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">client = pymongo.MongoClient(host=<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'localhost'</span>, port=<span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">27017</span>)</span></p>这样就可以创建MongoDB的连接对象了。
另外，MongoClient的第一个参数host还可以直接传入MongoDB的连接字符串，它以mongodb开头，例如：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">client = MongoClient(<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'mongodb://localhost:27017/'</span>)</span></p>这也可以达到同样的连接效果。
2.指定数据集
MongoDB中可以建立多个数据库，接下来我们需要指定操作哪个数据库。这里我们以test数据库为例来说明，下一步需要在程序中指定要使用的数据库：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">db = client.test</span></p>这里调用client的test属性即可返回test数据库。当然，我们也可以这样指定：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">db = client[<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'test'</span>]</span></p>这两种方式是等价的。
3.指定集合
MongoDB的每个数据库又包含许多集合（collection），它们类似于关系型数据库中的表。
下一步需要指定要操作的集合，这里指定一个集合名称为students。与指定数据库类似，指定集合也有两种方式：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">collection = db.students</span></p><p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">collection = db[<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'students'</span>]</span></p>这样我们便声明了一个Collection对象。
4.插入数据
接下来，便可以插入数据了。对于students这个集合，新建一条学生数据，这条数据以字典形式表示：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">student = {<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'id'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'20170101'</span>,<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'name'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'Jordan'</span>,<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'age'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">20</span>,<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'gender'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'male'</span><br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">}</span></p>这里指定了学生的学号、姓名、年龄和性别。接下来，直接调用collection的insert()方法即可插入数据，代码如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">result = collection.insert(student) print(result)</span></p>在MongoDB中，每条数据其实都有一个_id属性来唯一标识。如果没有显式指明该属性，MongoDB会自动产生一个ObjectId类型的_id属性。insert()方法会在执行后返回_id值。
运行结果如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;"><span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">5932</span>a68615c2606814c91f3d</span></p>当然，我们也可以同时插入多条数据，只需要以列表形式传递即可，示例如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">student1 = {<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'id'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'20170101'</span>,<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'name'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'Jordan'</span>,<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'age'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">20</span>,<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'gender'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'male'</span><br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">}<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"><br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">student2 = {<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'id'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'20170202'</span>,<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'name'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'Mike'</span>,<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'age'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">21</span>,<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'gender'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'male'</span><br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">}<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"><br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">result = collection.insert([student1, student2])<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">print(result)</span></p>返回结果是对应的_id的集合：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">[ObjectId(<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'5932a80115c2606a59e8a048'</span>), ObjectId(<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'5932a80115c2606a59e8a049'</span>)]</span></p>实际上，在PyMongo 3.x版本中，官方已经不推荐使用insert()方法了。当然，继续使用也没有什么问题。官方推荐使用insert_one()和insert_many()方法来分别插入单条记录和多条记录，示例如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">student = {<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'id'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'20170101'</span>,<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'name'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'Jordan'</span>,<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'age'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">20</span>,<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'gender'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'male'</span><br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">}<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"><br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">result = collection.insert_one(student)<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">print(result)<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">print(result.inserted_id)</span></p>运行结果如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;"><pymongo.results.InsertOneResult object at <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">0x10d68b558</span>><br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"><span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">5932</span>ab0f15c2606f0c1cf6c5</span></p>与insert()方法不同，这次返回的是InsertOneResult对象，我们可以调用其inserted_id属性获取_id。
对于insert_many()方法，我们可以将数据以列表形式传递，示例如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">student1 = {<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'id'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'20170101'</span>,<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'name'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'Jordan'</span>,<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'age'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">20</span>,<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'gender'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'male'</span><br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">}<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"><br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">student2 = {<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'id'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'20170202'</span>,<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'name'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'Mike'</span>,<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'age'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">21</span>,<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'gender'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'male'</span><br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">}<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"><br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">result = collection.insert_many([student1, student2])<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">print(result)<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">print(result.inserted_ids)</span></p>运行结果如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;"><pymongo.results.InsertManyResult object at <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">0x101dea558</span>><br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">[ObjectId(<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'5932abf415c2607083d3b2ac'</span>), ObjectId(<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'5932abf415c2607083d3b2ad'</span>)]</span></p>该方法返回的类型是InsertManyResult，调用inserted_ids属性可以获取插入数据的_id列表。
5.查询数据库
插入数据后，我们可以利用find_one()或find()方法进行查询，其中find_one()查询得到的是单个结果，find()则返回一个生成器对象。示例如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">result = collection.find_one({<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'name'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'Mike'</span>})<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">print(type(result))<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">print(result)</span></p>这里我们查询name为Mike的数据，它的返回结果是字典类型，运行结果如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;"><class 'dict'><br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">{'_id': ObjectId('5932a80115c2606a59e8a049'), 'id': '20170202', 'name': 'Mike', 'age': 21, 'gender': 'male'}</span></p>可以发现，它多了_id属性，这就是MongoDB在插入过程中自动添加的。
此外，我们也可以根据ObjectId来查询，此时需要使用bson库里面的objectid：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;"><span class="" style="font-size: 15px;max-width: 100%;font-weight: bold;box-sizing: border-box !important;word-wrap: break-word !important;">from</span> bson.objectid <span class="" style="font-size: 15px;max-width: 100%;font-weight: bold;box-sizing: border-box !important;word-wrap: break-word !important;">import</span> ObjectId<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"><br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">result = collection.find_one({<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'_id'</span>: ObjectId(<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'593278c115c2602667ec6bae'</span>)})<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">print(result)</span></p>其查询结果依然是字典类型，具体如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">{<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'_id'</span>: ObjectId(<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'593278c115c2602667ec6bae'</span>), <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'id'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'20170101'</span>, <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'name'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'Jordan'</span>, <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'age'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">20</span>, <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'gender'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'male'</span>}</span></p>当然，如果查询结果不存在，则会返回None。
对于多条数据的查询，我们可以使用find()方法。例如，这里查找年龄为20的数据，示例如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">results = collection.find({<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'age'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">20</span>})<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">print(results)<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"><span class="" style="font-size: 15px;max-width: 100%;font-weight: bold;box-sizing: border-box !important;word-wrap: break-word !important;">for</span> result <span class="" style="font-size: 15px;max-width: 100%;font-weight: bold;box-sizing: border-box !important;word-wrap: break-word !important;">in</span> results:<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"> print(result)</span></p>运行结果如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;"><pymongo.cursor.Cursor object at <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">0x1032d5128</span>><br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">{<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'_id'</span>: ObjectId(<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'593278c115c2602667ec6bae'</span>), <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'id'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'20170101'</span>, <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'name'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'Jordan'</span>, <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'age'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">20</span>, <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'gender'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'male'</span>}<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">{<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'_id'</span>: ObjectId(<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'593278c815c2602678bb2b8d'</span>), <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'id'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'20170102'</span>, <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'name'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'Kevin'</span>, <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'age'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">20</span>, <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'gender'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'male'</span>}<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">{<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'_id'</span>: ObjectId(<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'593278d815c260269d7645a8'</span>), <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'id'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'20170103'</span>, <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'name'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'Harden'</span>, <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'age'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">20</span>, <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'gender'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'male'</span>}</span></p>返回结果是Cursor类型，它相当于一个生成器，我们需要遍历取到所有的结果，其中每个结果都是字典类型。
如果要查询年龄大于20的数据，则写法如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">results = collection.find({<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'age'</span>: {<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'$gt'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">20</span>}})</span></p>这里查询的条件键值已经不是单纯的数字了，而是一个字典，其键名为比较符号$gt，意思是大于，键值为20。这里将比较符号归纳为下表。
另外，还可以进行正则匹配查询。例如，查询名字以M开头的学生数据，示例如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">results = collection.find({<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'name'</span>: {<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'$regex'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'^M.*'</span>}})</span></p>这里使用$regex来指定正则匹配，^M.*代表以M开头的正则表达式。
这里将一些功能符号再归类为下表。
6.查询计数
要统计查询结果有多少条数据，可以调用count()方法。比如，统计所有数据条数：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">count = collection.find().count() print(count)</span></p>或者统计符合某个条件的数据：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">count = collection.find({<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'age'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">20</span>}).count()<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">print(count)</span></p>运行结果是一个数值，即符合条件的数据条数。
7.数据排序
排序时，直接调用sort()方法，并在其中传入排序的字段及升降序标志即可。示例如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">results = collection.find().sort(<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'name'</span>, pymongo.ASCENDING)<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">print([result[<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'name'</span>] <span class="" style="font-size: 15px;max-width: 100%;font-weight: bold;box-sizing: border-box !important;word-wrap: break-word !important;">for</span> result <span class="" style="font-size: 15px;max-width: 100%;font-weight: bold;box-sizing: border-box !important;word-wrap: break-word !important;">in</span> results])</span></p>运行结果如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">[<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'Harden'</span>, <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'Jordan'</span>, <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'Kevin'</span>, <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'Mark'</span>, <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'Mike'</span>]</span></p>这里我们调用pymongo.ASCENDING指定升序。如果要降序排列，可以传入pymongo.DESCENDING。
8.数据的偏移
在某些情况下，我们可能想只取某几个元素，这时可以利用skip()方法偏移几个位置，比如偏移2，就忽略前两个元素，得到第三个及以后的元素：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">results = collection.find().sort(<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'name'</span>, pymongo.ASCENDING).skip(<span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">2</span>)<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">print([result[<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'name'</span>] <span class="" style="font-size: 15px;max-width: 100%;font-weight: bold;box-sizing: border-box !important;word-wrap: break-word !important;">for</span> result <span class="" style="font-size: 15px;max-width: 100%;font-weight: bold;box-sizing: border-box !important;word-wrap: break-word !important;">in</span> results])</span></p>运行结果如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">[<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'Kevin'</span>, <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'Mark'</span>, <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'Mike'</span>]</span></p>另外，还可以用limit()方法指定要取的结果个数，示例如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">results = collection.find().sort(<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'name'</span>, pymongo.ASCENDING).skip(<span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">2</span>).limit(<span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">2</span>)<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">print([result[<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'name'</span>] <span class="" style="font-size: 15px;max-width: 100%;font-weight: bold;box-sizing: border-box !important;word-wrap: break-word !important;">for</span> result <span class="" style="font-size: 15px;max-width: 100%;font-weight: bold;box-sizing: border-box !important;word-wrap: break-word !important;">in</span> results])</span></p>运行结果如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">[<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'Kevin'</span>, <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'Mark'</span>]</span></p>如果不使用limit()方法，原本会返回三个结果，加了限制后，会截取两个结果返回。
值得注意的是，在数据库数量非常庞大的时候，如千万、亿级别，最好不要使用大的偏移量来查询数据，因为这样很可能导致内存溢出。此时可以使用类似如下操作来查询：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;"><span class="" style="font-size: 15px;max-width: 100%;font-weight: bold;box-sizing: border-box !important;word-wrap: break-word !important;">from</span> bson.objectid <span class="" style="font-size: 15px;max-width: 100%;font-weight: bold;box-sizing: border-box !important;word-wrap: break-word !important;">import</span> ObjectId<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">collection.find({<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'_id'</span>: {<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'$gt'</span>: ObjectId(<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'593278c815c2602678bb2b8d'</span>)}})</span></p>这时需要记录好上次查询的_id。
9.更新数据库
对于数据更新，我们可以使用update()方法，指定更新的条件和更新后的数据即可。例如：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">condition = {<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'name'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'Kevin'</span>}<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">student = collection.find_one(condition)<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">student[<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'age'</span>] = <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">25</span><br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">result = collection.update(condition, student)<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">print(result)</span></p>这里我们要更新name为Kevin的数据的年龄：首先指定查询条件，然后将数据查询出来，修改年龄后调用update()方法将原条件和修改后的数据传入。
运行结果如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">{<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'ok'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">1</span>, <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'nModified'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">1</span>, <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'n'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">1</span>, <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'updatedExisting'</span>: <span class="" style="font-size: 15px;max-width: 100%;font-weight: bold;box-sizing: border-box !important;word-wrap: break-word !important;">True</span>}</span></p>返回结果是字典形式，ok代表执行成功，nModified代表影响的数据条数。
另外，我们也可以使用$set操作符对数据进行更新，代码如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">result = collection.update(condition, {<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'$set'</span>: student})</span></p>这样可以只更新student字典内存在的字段。如果原先还有其他字段，则不会更新，也不会删除。而如果不用$set的话，则会把之前的数据全部用student字典替换；如果原本存在其他字段，则会被删除。
另外，update()方法其实也是官方不推荐使用的方法。这里也分为update_one()方法和update_many()方法，用法更加严格，它们的第二个参数需要使用$类型操作符作为字典的键名，示例如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">condition = {<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'name'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'Kevin'</span>}<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">student = collection.find_one(condition)<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">student[<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'age'</span>] = <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">26</span><br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">result = collection.update_one(condition, {<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'$set'</span>: student})<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">print(result)<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">print(result.matched_count, result.modified_count)</span></p>这里调用了update_one()方法，第二个参数不能再直接传入修改后的字典，而是需要使用{'$set': student}这样的形式，其返回结果是UpdateResult类型。然后分别调用matched_count和modified_count属性，可以获得匹配的数据条数和影响的数据条数。
运行结果如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;"><pymongo.results.UpdateResult object at <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">0x10d17b678</span>><br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"><span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">1</span> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">0</span></span></p>我们再看一个例子：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">condition = {<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'age'</span>: {<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'$gt'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">20</span>}}<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">result = collection.update_one(condition, {<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'$inc'</span>: {<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'age'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">1</span>}})<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">print(result)<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">print(result.matched_count, result.modified_count)</span></p>这里指定查询条件为年龄大于20，然后更新条件为{'$inc': {'age': 1}}，也就是年龄加1，执行之后会将第一条符合条件的数据年龄加1。
运行结果如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;"><pymongo.results.UpdateResult object at <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">0x10b8874c8</span>><br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"><span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">1</span> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">1</span></span></p>可以看到匹配条数为1条，影响条数也为1条。
如果调用update_many()方法，则会将所有符合条件的数据都更新，示例如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">condition = {<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'age'</span>: {<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'$gt'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">20</span>}}<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">result = collection.update_many(condition, {<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'$inc'</span>: {<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'age'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">1</span>}})<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">print(result)<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">print(result.matched_count, result.modified_count)</span></p>这时匹配条数就不再为1条了，运行结果如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;"><pymongo.results.UpdateResult object at <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">0x10c6384c8</span>><br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"><span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">3</span> <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">3</span></span></p>可以看到，这时所有匹配到的数据都会被更新。
10.数据删除
删除操作比较简单，直接调用remove()方法指定删除的条件即可，此时符合条件的所有数据均会被删除。示例如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">result = collection.remove({<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'name'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'Kevin'</span>})<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">print(result)</span></p>运行结果如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">{<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'ok'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">1</span>, <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'n'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">1</span>}</span></p>另外，这里依然存在两个新的推荐方法——delete_one()和delete_many()。示例如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;">result = collection.delete_one({<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'name'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'Kevin'</span>})<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">print(result)<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">print(result.deleted_count)<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">result = collection.delete_many({<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'age'</span>: {<span class="" style="font-size: 15px;max-width: 100%;color: rgb(221, 17, 68);box-sizing: border-box !important;word-wrap: break-word !important;">'$lt'</span>: <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">25</span>}})<br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;">print(result.deleted_count)</span></p>运行结果如下：
<p style="padding: 0.5em;max-width: 100%;font-size: 0.85em;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;border-radius: 3px;border-width: 1px;border-style: solid;border-color: rgb(204, 204, 204);margin-left: 0px;margin-right: 0px;box-sizing: border-box !important;word-wrap: break-word !important;display: block !important;"><span style="font-size: 15px;"><pymongo.results.DeleteResult object at <span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">0x10e6ba4c8</span>><br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"><span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">1</span><br style="max-width: 100%;box-sizing: border-box !important;word-wrap: break-word !important;"><span class="" style="font-size: 15px;max-width: 100%;color: rgb(0, 128, 128);box-sizing: border-box !important;word-wrap: break-word !important;">4</span></span></p>delete_one()即删除第一条符合条件的数据，delete_many()即删除所有符合条件的数据。它们的返回结果都是DeleteResult类型，可以调用deleted_count属性获取删除的数据条数。
本文是对PyMongo的一个入门介绍，更多详细用法，可以参见官方文档：http://api.mongodb.com/python/current/api/pymongo/collection.html
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