原文地址：http://www.oschina.net/translate/mongodb-how-to-limit-results

在这篇文章我们将看一下怎样在MongoDB限制结果同样怎样去分页显示。MongoDB使用limit去限制许多返回结果，MongoDB使用skip去跳转来自结果集中的记录，使用limit并结合skip能使你在MongoDB中做到分页。

让我们看一下这是怎样工作的

开始插入以下数据到你的MongoDB数据库里

db.Blog.insert( { name : "Denis",  age : 20, city : "Princeton" } )
db.Blog.insert( { name : "Abe",    age : 30, city : "Amsterdam" } )
db.Blog.insert( { name : "John",   age : 40, city : "New York"  } )
db.Blog.insert( { name : "Xavier", age : 10, city : "Barcelona" } )
db.Blog.insert( { name : "Zen",    age : 50, city : "Kyoto"     } )

db.Blog.find()

{ "_id" : ObjectId("51028ae0a8c33b71ed76a807"), "name" : "Denis", "age" : 20, "city" : "Princeton" }
{ "_id" : ObjectId("51028ae0a8c33b71ed76a808"), "name" : "Abe", "age" : 30, "city" : "Amsterdam" }
{ "_id" : ObjectId("51028ae2a8c33b71ed76a809"), "name" : "John", "age" : 40, "city" : "New York" }
{ "_id" : ObjectId("51028ae2a8c33b71ed76a80a"), "name" : "Xavier", "age" : 10, "city" : "Barcelona" }
{ "_id" : ObjectId("51028ae4a8c33b71ed76a80b"), "name" : "Zen", "age" : 50, "city" : "Kyoto" }

限制 MongoDB 的结果集数量

仅仅返回集合中插入第一个和第二个的条目

db.Blog.find().limit(2)

{ "_id" : ObjectId("5103e22c88a39c3c0b2585e1"), "name" : "Denis", "age" : 20, "city" : "Princeton" }
{ "_id" : ObjectId("5103e22d88a39c3c0b2585e2"), "name" : "Abe", "age" : 30, "city" : "Amsterdam" }

即使那样我们也能添加排序，运行下面

db.Blog.find().sort({name: 1}).limit(2)

{ "_id" : ObjectId("5103e22d88a39c3c0b2585e2"), "name" : "Abe", "age" : 30, "city" : "Amsterdam" }
{ "_id" : ObjectId("5103e22c88a39c3c0b2585e1"), "name" : "Denis", "age" : 20, "city" : "Princeton" }

运行下面

db.Blog.find(null, {name: 1, _id: 0}).sort({name: 1}).limit(2)

{ "name" : "Abe" }
{ "name" : "Denis" }

MongoDB 数据分页

现在让我们看一下怎样返回插入的第三个和第四个的条目，这应该是John和Xavier。这种情况我们需要使用skip我们得在后面添加skip(2)

这里的命令看起来像什么，运行下面语句

db.Blog.find(null, {name: 1, _id: 0}).sort({name: 1}).limit(2).skip(2)

{ "name" : "John" }
{ "name" : "Xavier" }

db.Blog.find(null, {name: 1, _id: 0}).sort({name: 1}).limit(2).skip(6)

db.Blog.find().sort( { $natural: -1 } )

{ "_id" : ObjectId("5103eaa688a39c3c0b2585ed"), "name" : "Zen", "age" : 50, "city" : "Kyoto" }
{ "_id" : ObjectId("5103eaa588a39c3c0b2585ec"), "name" : "Xavier", "age" : 10, "city" : "Barcelona" }
{ "_id" : ObjectId("5103eaa588a39c3c0b2585eb"), "name" : "John", "age" : 40, "city" : "New York" }
{ "_id" : ObjectId("5103eaa588a39c3c0b2585ea"), "name" : "Abe", "age" : 30, "city" : "Amsterdam" }
{ "_id" : ObjectId("5103eaa588a39c3c0b2585e9"), "name" : "Denis", "age" : 20, "city" : "Princeton" }

当使用sort()出现的一个警告，要注意下面的限制

Warning ：排序功能需要整个排序在32兆字节里才能够完成。当排序选项超过了32兆，MongoDB将返回一个错误。应使用 cursor.limit()或在字段中创建一个角标那样你能避免这个错误(Warning The sort function requires that the entire sort be able to complete within 32 megabytes. When the sort option consumes more than 32 megabytes, MongoDB will return an error. Use cursor.limit(), or create an index on the field that you’re sorting to avoid this error.)

这是所有的文章，如果你对我其它MongoDB文章感兴趣，你能在这儿找到它们：

Install MongoDB as a Windows Service
UPSERTs with MongoDB
How to sort results in MongoDB
Indexes in MongoDB: A quick overview
Multidocument updates with MongoDB
MongoDB: How to include and exclude the fields you want in results