MongoDB 查询文档

在本章中，我们将学习如何从MongoDB集合中查询文档。

find()方法

要从MongoDB集合中查询数据，您需要使用MongoDB的 find() 方法。

语法

find() 方法的基本语法如下 –

>db.COLLECTION_NAME.find()

find() 方法将以非结构化的方式显示所有文档。

示例

假设我们已经创建了一个名为mycol的集合，如下所示：

> use sampleDB
switched to db sampleDB
> db.createCollection("mycol")
{ "ok" : 1 }
>

通过使用如下所示的insert()方法，将其中插入了3个文档。

> db.mycol.insert([
    {
        title: "MongoDB Overview",
        description: "MongoDB is no SQL database",
        by: "tutorials point",
        url: "http://www.tutorialspoint.com",
        tags: ["mongodb", "database", "NoSQL"],
        likes: 100
    },
    {
        title: "NoSQL Database",
        description: "NoSQL database doesn't have tables",
        by: "tutorials point",
        url: "http://www.tutorialspoint.com",
        tags: ["mongodb", "database", "NoSQL"],
        likes: 20,
        comments: [
            {
                user:"user1",
                message: "My first comment",
                dateCreated: new Date(2013,11,10,2,35),
                like: 0
            }
        ]
    }
])

以下方法获取集合中的所有文档 −

> db.mycol.find()
{ "_id" : ObjectId("5dd4e2cc0821d3b44607534c"), "title" : "MongoDB Overview", "description" : "MongoDB is no SQL database", "by" : "tutorials point", "url" : "http://www.tutorialspoint.com", "tags" : [ "mongodb", "database", "NoSQL" ], "likes" : 100 }
{ "_id" : ObjectId("5dd4e2cc0821d3b44607534d"), "title" : "NoSQL Database", "description" : "NoSQL database doesn't have tables", "by" : "tutorials point", "url" : "http://www.tutorialspoint.com", "tags" : [ "mongodb", "database", "NoSQL" ], "likes" : 20, "comments" : [ { "user" : "user1", "message" : "My first comment", "dateCreated" : ISODate("2013-12-09T21:05:00Z"), "like" : 0 } ] }
>

pretty() 方法

以格式化的方式显示结果，您可以使用pretty()方法。

语法

>db.COLLECTION_NAME.find().pretty()

示例

以下示例从名为mycol的集合中检索所有文档，并以易于阅读的格式排列它们。

> db.mycol.find().pretty()
{
    "_id" : ObjectId("5dd4e2cc0821d3b44607534c"),
    "title" : "MongoDB Overview",
    "description" : "MongoDB is no SQL database",
    "by" : "tutorials point",
    "url" : "http://www.tutorialspoint.com",
    "tags" : [
        "mongodb",
        "database",
        "NoSQL"
    ],
    "likes" : 100
}
{
    "_id" : ObjectId("5dd4e2cc0821d3b44607534d"),
    "title" : "NoSQL Database",
    "description" : "NoSQL database doesn't have tables",
    "by" : "tutorials point",
    "url" : "http://www.tutorialspoint.com",
    "tags" : [
        "mongodb",
        "database",
        "NoSQL"
    ],
    "likes" : 20,
    "comments" : [
        {
            "user" : "user1",
            "message" : "My first comment",
            "dateCreated" : ISODate("2013-12-09T21:05:00Z"),
            "like" : 0
        }
    ]
}

findOne()方法

除了find()方法外，还有一个 findOne() 方法，它将只返回一个文档。

语法

>db.COLLECTIONNAME.findOne()

示例

以下示例检索标题为“MongoDB概述”的文档。

> db.mycol.findOne({title: "MongoDB Overview"})
{
    "_id" : ObjectId("5dd6542170fb13eec3963bf0"),
    "title" : "MongoDB Overview",
    "description" : "MongoDB is no SQL database",
    "by" : "tutorials point",
    "url" : "http://www.tutorialspoint.com",
    "tags" : [
        "mongodb",
        "database",
        "NoSQL"
    ],
    "likes" : 100
}

RDBMS在MongoDB中的Where子句等效操作

要根据某些条件查询文档，您可以使用以下操作。

操作	语法	示例	RDBMS对应的语句
相等	`{<key>:{$eg;<value>}}`	`db.mycol.find({"by":"tutorials point"}).pretty()`	where by = ‘tutorials point’
小于	`{<key>:{$lt:<value>}}`	`db.mycol.find({"likes":{$lt:50}}).pretty()`	where likes < 50
小于等于	`{<key>:{$lte:<value>}}`	`db.mycol.find({"likes":{$lte:50}}).pretty()`	where likes <= 50
大于	`{<key>:{$gt:<value>}}`	`db.mycol.find({"likes":{$gt:50}}).pretty()`	where likes > 50
大于等于	`{<key>:{$gte:<value>}}`	`db.mycol.find({"likes":{$gte:50}}).pretty()`	where likes >= 50
不相等	`{<key>:{$ne:<value>}}`	`db.mycol.find({"likes":{$ne:50}}).pretty()`	where likes != 50
数组中的值	`{<key>:{$in:[<value1>, <value2>,……<valueN>]}}`	`db.mycol.find({"name":{$in:["Raj", "Ram", "Raghu"]}}).pretty()`	Where name 匹配数组中任何一个值:[“Raj”, “Ram”, “Raghu”]
不在数组中的值	`{<key>:{$nin:<value>}}`	`db.mycol.find({"name":{$nin:["Ramu", "Raghav"]}}).pretty()`	Where name 值不在数组中:[“Ramu”, “Raghav”] 或者不存在

MongoDB中的AND

语法

要基于AND条件查询文档，需要使用$and关键字。以下是AND的基本语法−

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

示例

以下示例将显示所有由“教程点”编写且标题为“MongoDB概述”的教程。

> db.mycol.find({$and:[{"by":"tutorials point"},{"title": "MongoDB Overview"}]}).pretty()
{
    "_id" : ObjectId("5dd4e2cc0821d3b44607534c"),
    "title" : "MongoDB Overview",
    "description" : "MongoDB is no SQL database",
    "by" : "tutorials point",
    "url" : "http://www.tutorialspoint.com",
    "tags" : [
        "mongodb",
        "database",
        "NoSQL"
    ],
    "likes" : 100
}
>

对于上面给出的例子，等效的where子句将是 ‘where by = ‘tutorials point’ AND title = ‘MongoDB Overview” 。您可以在find子句中传递任意数量的键值对。

在MongoDB中的OR操作符

语法

要根据OR条件查询文档，您需要使用 $or 关键字。以下是基本语法 OR –

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

示例

下面的示例将显示所有由“tutorials point”编写或标题为“MongoDB概述”的教程。

>db.mycol.find({$or:[{"by":"tutorials point"},{"title": "MongoDB Overview"}]}).pretty()
{
   "_id": ObjectId(7df78ad8902c),
   "title": "MongoDB Overview", 
   "description": "MongoDB is no sql database",
   "by": "tutorials point",
   "url": "http://www.tutorialspoint.com",
   "tags": ["mongodb", "database", "NoSQL"],
   "likes": "100"
}
>

同时使用AND和OR

示例

以下示例将显示likes大于10且标题是’MongoDB概述’或by是’tutorials point’的文档。等效的SQL where子句为 ‘where likes >10 AND (by = ‘tutorials point’ OR title = ‘MongoDB概述’)’

>db.mycol.find({"likes": { $gt:10},$ or: [{"by": "tutorials point"},
   {"title": "MongoDB Overview"}]}).pretty()
{
   "_id": ObjectId(7df78ad8902c),
   "title": "MongoDB Overview", 
   "description": "MongoDB is no sql database",
   "by": "tutorials point",
   "url": "http://www.tutorialspoint.com",
   "tags": ["mongodb", "database", "NoSQL"],
   "likes": "100"
}
>

在MongoDB中的NOR条件

语法

要根据NOT条件查询文档，您需要使用$not关键字。以下是基本语法： NOT −

>db.COLLECTION_NAME.find(
    {
        $not: [
            {key1: value1}, {key2:value2}
        ]
    }
)

示例

假设我们在集合 empDetails 中插入了3个文档，如下所示-

db.empDetails.insertMany(
    [
        {
            First_Name: "Radhika",
            Last_Name: "Sharma",
            Age: "26",
            e_mail: "radhika_sharma.123@gmail.com",
            phone: "9000012345"
        },
        {
            First_Name: "Rachel",
            Last_Name: "Christopher",
            Age: "27",
            e_mail: "Rachel_Christopher.123@gmail.com",
            phone: "9000054321"
        },
        {
            First_Name: "Fathima",
            Last_Name: "Sheik",
            Age: "24",
            e_mail: "Fathima_Sheik.123@gmail.com",
            phone: "9000054321"
        }
    ]
)

下面的例子将检索不是“Radhika”的名字和不是“Christopher”的姓氏的文档。

> db.empDetails.find(
    {
        $nor:[
            40
            {"First_Name": "Radhika"},
            {"Last_Name": "Christopher"}
        ]
    }
).pretty()
{
    "_id" : ObjectId("5dd631f270fb13eec3963bef"),
    "First_Name" : "Fathima",
    "Last_Name" : "Sheik",
    "Age" : "24",
    "e_mail" : "Fathima_Sheik.123@gmail.com",
    "phone" : "9000054321"
}

MongoDB中NOT

语法

要根据NOT条件查询文档，您需要使用$not关键字，以下是基本语法： NOT −

>db.COLLECTION_NAME.find(
    {
        $NOT: [
            {key1: value1}, {key2:value2}
        ]
    }
).pretty()

示例

以下示例将检索年纪不大于25的文档。

> db.empDetails.find( { "Age": {  $not: {$ gt: "25" } } } )
{
    "_id" : ObjectId("5dd6636870fb13eec3963bf7"),
    "First_Name" : "Fathima",
    "Last_Name" : "Sheik",
    "Age" : "24",
    "e_mail" : "Fathima_Sheik.123@gmail.com",
    "phone" : "9000054321"
}