1. 前言

　　在这篇博文中，我们将学习如何查询mongoDB中的数据。当我们把数据存储在mongoDB以后，我们需要把数据查询出来。毕竟CRUD操作中，查询操作在我们系统中是我们应用比较频繁的操作。我们需要应对不同的业务需求，构造合适的查询条件去查询我们想要的数据。我们需要去学习mongoDB给我们提供了哪些查询相关的语法和功能。在这里，我们使用mongodb自带的mongo shell（mongo shell是一个javascript环境的mongodb客户端，支持js语法）来学习。

2. 准备

　　在开始之前，我们需要准备一下实验用的数据：

// 启动mongo shell客户端$ mongo// 在这里我们使用test数据库，如果没有这个数据库，会自动创建> use test// 在users collection中插入6条用户数据> db.users.insertMany( [   {    _id: 1,    name: "sue",    age: 19,    type: 1,    status: "P",    favorites: { artist: "Picasso", food: "pizza" },    finished: [ 17, 3 ],    badges: [ "blue", "black" ],    points: [     { points: 85, bonus: 20 },     { points: 85, bonus: 10 }    ]   },   {    _id: 2,    name: "bob",    age: 42,    type: 1,    status: "A",    favorites: { artist: "Miro", food: "meringue" },    finished: [ 11, 25 ],    badges: [ "green" ],    points: [     { points: 85, bonus: 20 },     { points: 64, bonus: 12 }    ]   },   {    _id: 3,    name: "ahn",    age: 22,    type: 2,    status: "A",    favorites: { artist: "Cassatt", food: "cake" },    finished: [ 6 ],    badges: [ "blue", "red" ],    points: [     { points: 81, bonus: 8 },     { points: 55, bonus: 20 }    ]   },   {    _id: 4,    name: "xi",    age: 34,    type: 2,    status: "D",    favorites: { artist: "Chagall", food: "chocolate" },    finished: [ 5, 11 ],    badges: [ "red", "black" ],    points: [     { points: 53, bonus: 15 },     { points: 51, bonus: 15 }    ]   },   {    _id: 5,    name: "xyz",    age: 23,    type: 2,    status: "D",    favorites: { artist: "Noguchi", food: "nougat" },    finished: [ 14, 6 ],    badges: [ "orange" ],    points: [     { points: 71, bonus: 20 }    ]   },   {    _id: 6,    name: "abc",    age: 43,    type: 1,    status: "A",    favorites: { food: "pizza", artist: "Picasso" },    finished: [ 18, 12 ],    badges: [ "black", "blue" ],    points: [     { points: 78, bonus: 8 },     { points: 57, bonus: 7 }    ]   } ])

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原标题：MongoDB的查询操作

关键词：MongoDB