Mongodb 简明教程

MongoDB - Query Document

在本章中，我们将学习如何从 MongoDB 集合查询文档。

In this chapter, we will learn how to query document from MongoDB collection.

The find() Method

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

To query data from MongoDB collection, you need to use MongoDB’s find() method.

Syntax

find() 方法的基本语法如下 −

The basic syntax of find() method is as follows −

>db.COLLECTION_NAME.find()

find() 方法将以非结构化的方式显示所有文档。

find() method will display all the documents in a non-structured way.

Example

假设我们创建了一个名为 mycol 的集合，如下所示 −

Assume we have created a collection named mycol as −

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

并使用 insert() 方法在其中插入了 3 个文档，如下所示 −

And inserted 3 documents in it using the insert() method as shown below −

> 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 −

Following method retrieves all the documents in the collection −

> 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 } ] }
>

The pretty() Method

要以格式化方式显示结果，可以使用 pretty() 方法。

To display the results in a formatted way, you can use pretty() method.

Syntax

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

Example

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对其进行排列。

Following example retrieves all the documents from the collection named mycol and arranges them in an easy-to-read format.

> 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
		}
	]
}

The findOne() method

除了 find() 方法外，还有 findOne() 方法，仅返回一个文档。

Apart from the find() method, there is findOne() method, that returns only one document.

Syntax

>db.COLLECTIONNAME.findOne()

Example

以下示例检索标题为 MongoDB Overview 的文档。

Following example retrieves the document with title MongoDB Overview.

> 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 Where Clause Equivalents in MongoDB

要根据某个条件查询文档，可以使用以下操作。

To query the document on the basis of some condition, you can use following operations.

Operation

Syntax

Example

RDBMS Equivalent

Equality

{<key>:{$eg;<value>}}

db.mycol.find({"by":"tutorials point"}).pretty()

where by = 'tutorials point'

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

Values in an array

{<key>:{$in:[<value1>, <value2>,……<valueN>]}}

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

{<key>:{$nin:<value>}}

db.mycol.find({"name":{$nin:["Ramu", "Raghav"]}}).pretty()

Where name values is not in the array :["Ramu", "Raghav"] or, doesn’t exist at all

AND in MongoDB

Syntax

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 −

To query documents based on the AND condition, you need to use $and keyword. Following is the basic syntax of AND −

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

Example

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

Following example will show all the tutorials written by 'tutorials point' and whose title is '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。

For the above given example, equivalent where clause will be ' where by = 'tutorials point' AND title = 'MongoDB Overview' '. You can pass any number of key, value pairs in find clause.

OR in MongoDB

Syntax

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 −

To query documents based on the OR condition, you need to use $or keyword. Following is the basic syntax of OR −

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

Example

以下示例将显示所有由“教程点”编写的教程，或其标题为“MongoDB 概述”的教程。

Following example will show all the tutorials written by 'tutorials point' or whose title is 'MongoDB Overview'.

>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"
}
>

Using AND and OR Together

Example

以下示例将显示喜欢次数大于 10，且其标题为“MongoDB 概述”或作者为“教程点”的文档。等效的 SQL where 子句是 'where likes>10 AND (by = 'tutorials point' OR title = 'MongoDB Overview')'

The following example will show the documents that have likes greater than 10 and whose title is either 'MongoDB Overview' or by is 'tutorials point'. Equivalent SQL where clause is '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"
}
>

NOR in MongoDB

Syntax

要基于 NOT 条件查询文档，您需要使用 $not 关键字。以下是 NOT 的基本语法 −

To query documents based on the NOT condition, you need to use $not keyword. Following is the basic syntax of NOT −

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

Example

假设我们在集合 empDetails 中插入了 3 个文档，如下所示 −

Assume we have inserted 3 documents in the collection empDetails as shown below −

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”，姓氏不是“Christopher”的文档

Following example will retrieve the document(s) whose first name is not "Radhika" and last name is not "Christopher"

> 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"
}

NOT in MongoDB

Syntax

要基于 NOT 条件查询文档，您需要使用 $not 关键字，以下是 NOT 的基本语法 −

To query documents based on the NOT condition, you need to use $not keyword following is the basic syntax of NOT −

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

Example

以下示例将检索年龄不大于 25 的文档

Following example will retrieve the document(s) whose age is not greater than 25

> 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"
}