Question

语法

基本的find()方法语法如下

>db.COLLECTION_NAME.find()

pretty() 方法

结果显示在一个格式化的方式，可以使用 pretty() 方法.

语法:

>db.mycol.find().pretty()

例子

> db.mycol.find().pretty()
{
    "_id" : ObjectId("5799c3eb235910620b89c674"),
    "title" : "MongoDB Overview",
    "description" : "MongoDB is no sql database",
    "by" : "tutorials itcast",
    "url" : "http://www.itcast.cn",
    "tags" : [
        "mongodb",
        "database",
        "NoSQL"
    ],
    "likes" : 100
}
{
    "_id" : ObjectId("5799c3f3235910620b89c675"),
    "title" : "MySQL Overview",
    "description" : "MySQL is sql database",
    "by" : "tutorials itcast",
    "url" : "http://www.itcast.cn",
    "tags" : [
        "MySQL",
        "database",
        "SQL"
    ],
    "likes" : 40
}
>

除了find() 方法外，还有一个 findOne() 法，返回一个结果。

db.mycol.findOne()

MongoDB 与 RDBMS Where 语句比较

操作	语法	例子	RDBMS 等同
Equality	{<key>:<value>}	db.mycol.find({"by":"tutorials itcast"}).pretty()	where by = 'tutorials itcast'
Less Than	{<key>:{$lt:<value>}}	db.mycol.find({"likes":{$lt:50}}).pretty()	where likes < 50
Less Than Equals	{<key>:{$lte:<value>}}	db.mycol.find({"likes":{$lte:50}}).pretty()	where likes <= 50
Greater Than	{<key>:{$gt:<value>}}	db.mycol.find({"likes":{$gt:50}}).pretty()	where likes > 50
Greater Than Equals	{<key>:{$gte:<value>}}	db.mycol.find({"likes":{$gte:50}}).pretty()	where likes >= 50
Not Equals	{<key>:{$ne:<value>}}	db.mycol.find({"likes":{$ne:50}}).pretty()	where likes != 50

AND 在MongoDB中用法

语法:

在 find() 方法，如果通过多个键分离','，那么 MongoDB 处理 AND 条件。AND 基本语法如下所示：

>db.mycol.find({key1:value1, key2:value2}).pretty()

例子

下面给出的例子将显示所有的教程，标题是“MongoDB Overview“

> db.mycol.find({"by":"tutorials itcast","title": "MongoDB Overview"}).pretty()
{
  "_id" : ObjectId("5799c3eb235910620b89c674"),
  "title" : "MongoDB Overview",
  "description" : "MongoDB is no sql database",
  "by" : "tutorials itcast",
  "url" : "http://www.itcast.cn",
  "tags" : [
    "mongodb",
    "database",
    "NoSQL"
  ],
  "likes" : 100
}
>

对于上面给出的例子相当于where子句 where by='tutorials itcast' AND title='MongoDB Overview'，可以通过任意数量的键值对在 find 子句。

MongoDB中OR

语法:

OR条件的基础上要查询文件，需要使用$or关键字。OR 基本语法如下所示：

>db.mycol.find(
   {
      $or: [
         {key1: value1}, {key2:value2}
      ]
   }
).pretty()

例子

下面给出的例子将显示所有的教程，标题是“MongoDB Overview'或'MySQL Overview'

>db.mycol.find({
  $or: [
    {
      "title": "MySQL Overview"
    },
    {
      "title": "MongoDB Overview"
    }
  ]
}).pretty()
{
  "_id" : ObjectId("57cefded600d5bb1e2acdb70"),
  "title" : "MongoDB Overview",
  "description" : "MongoDB is no sql database",
  "by" : "tutorials itcast",
  "url" : "http://www.itcast.cn",
  "tags" : [
    "mongodb",
    "database",
    "NoSQL"
  ],
  "likes" : 100
}
{
  "_id" : ObjectId("57cefdf7600d5bb1e2acdb71"),
  "title" : "MySQL Overview",
  "description" : "MySQL is sql database",
  "by" : "tutorials itcast",
  "url" : "http://www.itcast.cn",
  "tags" : [
    "MySQL",
    "database",
    "SQL"
  ],
  "likes" : 40
}
>

AND 和 OR 一起使用

例子

下面给出的例子将显示 喜爱数高于50，其标题是MongoDB Overview或者是itcast所写 。等效于 SQL where子句 为 where likes>10 AND (by = 'itcast' OR title = 'MongoDB Overview')

> db.mycol.find({
  "likes": {
    $gt: 50
  },
  $or: [
    {
      "by": "tutorials itcast"
    },
    {
      "title": "MongoDB Overview"
    }
  ]
}).pretty()
{
  "_id" : ObjectId("57cefded600d5bb1e2acdb70"),
  "title" : "MongoDB Overview",
  "description" : "MongoDB is no sql database",
  "by" : "tutorials itcast",
  "url" : "http://www.itcast.cn",
  "tags" : [
    "mongodb",
    "database",
    "NoSQL"
  ],
  "likes" : 100
}
>