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📜  MongoDB-查询文档

📅  最后修改于: 2020-11-27 05:53:08             🧑  作者: Mango

在本章中，我们将学习如何从MongoDB集合中查询文档。

find()方法

要查询MongoDB集合中的数据，您需要使用MongoDB的find()方法。

句法

find()方法的基本语法如下：

>db.COLLECTION_NAME.find()

find()方法将以非结构化方式显示所有文档。

例

假设我们已经创建了一个名为mycol的集合-

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

并使用insert()方法在其中插入3个文档，如下所示-

> 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
            }
        ]
    }
])

以下方法检索集合中的所有文档-

> 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

要以格式化的方式显示结果，可以使用pretty()方法。

句法

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

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()方法之外，还有findOne()方法，该方法仅返回一个文档。

句法

>db.COLLECTIONNAME.findOne()

例

以下示例检索标题为MongoDB Overview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，其中MongoDB中的子句等效

要根据某些条件查询文档，可以使用以下操作。

Operation Syntax Example RDBMS Equivalent
Equality {:{$eg;}} db.mycol.find({“by”:”tutorials point”}).pretty() where by = ‘tutorials point’
Less Than {:{$lt:}} db.mycol.find({“likes”:{$lt:50}}).pretty() where likes < 50
Less Than Equals {:{$lte:}} db.mycol.find({“likes”:{$lte:50}}).pretty() where likes <= 50
Greater Than {:{$gt:}} db.mycol.find({“likes”:{$gt:50}}).pretty() where likes > 50
Greater Than Equals {:{$gte:}} db.mycol.find({“likes”:{$gte:50}}).pretty() where likes >= 50
Not Equals {:{$ne:}} db.mycol.find({“likes”:{$ne:50}}).pretty() where likes != 50
Values in an array {:{$in:[, ,……]}} db.mycol.find({“name”:{$in:[“Raj”, “Ram”, “Raghu”]}}).pretty() Where name matches any of the value in :[“Raj”, “Ram”, “Raghu”]
Values not in an array {:{$nin:}} db.mycol.find({“name”:{$nin:[“Ramu”, “Raghav”]}}).pretty() Where name values is not in the array :[“Ramu”, “Raghav”] or, doesn’t exist at all

在MongoDB中

句法

要基于AND条件查询文档，您需要使用$ and关键字。以下是AND的基本语法-

>db.mycol.find({ $and: [ {:}, { :} ] })

例

以下示例将显示所有由“ tutorials point”编写的教程，其标题为“ MongoDB Overview”。

> 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
}
>

对于上面给出的示例，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。

或在MongoDB中

句法

要基于OR条件查询文档，您需要使用$ or关键字。以下是OR的基本语法-

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

例

以下示例将显示所有由“ tutorials point”编写或标题为“ MongoDB Overview”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"
}
>

一起使用AND和OR

例

下面的示例将显示点赞大于10且标题为“ MongoDB概述”或by为“ tutorials point”的文档。等价的SQL where子句为‘where likes> 10 AND(by =’tutorials point’OR title =’MongoDB Overview’)

>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"
}
>

MongoDB中的NOR

句法

要根据NOT条件查询文档，需要使用$ not关键字。以下是NOT的基本语法-

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

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"
        }
    ]
)

以下示例将检索名字不是“ Radhika”且名字不是“ Christopher”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"
}

不在MongoDB中

句法

要根据NOT条件查询文档，您需要使用$ not关键字，这是NOT的基本语法-

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

例

以下示例将检索年龄不超过25岁的文档

> 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"
}