MongoDB 查询文档

喔28 • • MongoDB 教程 • 683 阅读

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

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

>db.COLLECTION_NAME.find([query],[projection])
参数
  • query - document [可选的]。使用查询操作符指定选择筛选器。若要返回集合中的所有文档，请省略此参数或传递一个空文档({})。
  • projection -document [可选的]。指定要在文档中返回与查询筛选器匹配的字段。要返回匹配文档中的所有字段，请省略此参数。有关详细信息，请参见投影。
示例
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: "蝴蝶教程",
url: "https://www.jc2182.com",
tags: ["mongodb", "database", "NoSQL"],
likes: 100
},
{
title: "NoSQL Database",
description: "NoSQL database doesn't have tables",
by: "蝴蝶教程",
url: "https://www.jc2182.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("5f474d67f4d867c5a4de6189"), "title" : "MongoDB Overview", "description" : "MongoDB is no SQL database", "by" : "蝴蝶教程", "url" : "https://www.jc2182.com", "tags" : [ "mongodb", "database", "NoSQL" ], "likes" : 100 }
{ "_id" : ObjectId("5f474d67f4d867c5a4de618a"), "title" : "NoSQL Database", "description" : "NoSQL database doesn't have tables", "by" : "蝴蝶教程", "url" : "https://www.jc2182.com", "tags" : [ "mongodb", "database", "NoSQL" ], "likes" : 20, "comments" : [ { "user" : "user1", "message" : "My first comment", "dateCreated" : ISODate("2013-12-09T18:35:00Z"), "like" : 0 } ] }

pretty() 方法

要以格式化的方式显示结果，可以使用pretty()方法。
语法 

>db.COLLECTION_NAME.find().pretty()
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("5f474d67f4d867c5a4de6189"),
"title" : "MongoDB Overview",
"description" : "MongoDB is no SQL database",
"by" : "蝴蝶教程",
"url" : "https://www.jc2182.com",
"tags" : [
"mongodb",
"database",
"NoSQL"
],
"likes" : 100
}
{
"_id" : ObjectId("5f474d67f4d867c5a4de618a"),
"title" : "NoSQL Database",
"description" : "NoSQL database doesn't have tables",
"by" : "蝴蝶教程",
"url" : "https://www.jc2182.com",
"tags" : [
"mongodb",
"database",
"NoSQL"
],
"likes" : 20,
"comments" : [
{
"user" : "user1",
"message" : "My first comment",
"dateCreated" : ISODate("2013-12-09T18:35:00Z"),
"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。
语法： 

>db.COLLECTIONNAME.findOne()
以下示例检索title为MongoDB Overview的文档。 

db.mycol.findOne({title: "MongoDB Overview"})
{
"_id" : ObjectId("5f474d67f4d867c5a4de6189"),
"title" : "MongoDB Overview",
"description" : "MongoDB is no SQL database",
"by" : "蝴蝶教程",
"url" : "https://www.jc2182.com",
"tags" : [
"mongodb",
"database",
"NoSQL"
],
"likes" : 100
}

>RDBMS(关系型数据库系统)中MongoDB中的子句等效

操作 例子 语法 RDBMS等效
相等 {<key>:{$eg;<value>}} db.mycol.find({"by":"蝴蝶教程"}).pretty() where by = '蝴蝶教程'
小于 {<key>:{$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":{$ne:50}}).pretty() where likes != 50
值在数组中 {<key>:{$in:[<value1>, <value2>,……<valueN>]}} db.mycol.find({"name":{$in:["Raj", "Ram", "Raghu"]}}).pretty() where name matches any of the value in :["Raj", "Ram", "Raghu"]
值不在数组中 {<key>:{$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

MongoDB中的AND

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-
语法： 

>db.mycol.find({ $and: [ {<key1>:<value1>}, { <key2>:<value2>} ] })
以下示例将显示所有由“蝴蝶教程”编写的教程，其标题为“MongoDB Overview”。 

db.mycol.find({$and:[{"by":"蝴蝶教程"},{"title": "MongoDB Overview"}]}).pretty()
{
"_id" : ObjectId("5f474d67f4d867c5a4de6189"),
"title" : "MongoDB Overview",
"description" : "MongoDB is no SQL database",
"by" : "蝴蝶教程",
"url" : "https://www.jc2182.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 ='蝴蝶教程'AND title ='MongoDB Overview''。您可以在find子句中传递任意数量的键，值对。

MongoDB中的OR

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-
语法： 

>db.mycol.find({ $or: [ {<key1>:<value1>}, { <key2>:<value2>} ] })
以下示例将显示所有由“蝴蝶教程”编写或标题为“MongoDB Overview”的教程。 

db.mycol.find({$or:[{"by":"蝴蝶教程"},{"title": "MongoDB Overview"}]}).pretty()
{
"_id" : ObjectId("5f474d67f4d867c5a4de6189"),
"title" : "MongoDB Overview",
"description" : "MongoDB is no SQL database",
"by" : "蝴蝶教程",
"url" : "https://www.jc2182.com",
"tags" : [
"mongodb",
"database",
"NoSQL"
],
"likes" : 100
}
{
"_id" : ObjectId("5f474d67f4d867c5a4de618a"),
"title" : "NoSQL Database",
"description" : "NoSQL database doesn't have tables",
"by" : "蝴蝶教程",
"url" : "https://www.jc2182.com",
"tags" : [
"mongodb",
"database",
"NoSQL"
],
"likes" : 20,
"comments" : [
{
"user" : "user1",
"message" : "My first comment",
"dateCreated" : ISODate("2013-12-09T18:35:00Z"),
"like" : 0
}
]
}

一起使用AND和OR

下面的示例将显示likes大于10且title为“MongoDB Overview”或by为“蝴蝶教程”的文档。等价的SQL where子句为'where likes> 10 AND（by ='蝴蝶教程'OR title ='MongoDB Overview'） 

db.mycol.find({"likes": {$gt:10}, $or: [{"by": "蝴蝶教程"},{"title": "MongoDB Overview"}]}).pretty()
{
"_id" : ObjectId("5f474d67f4d867c5a4de6189"),
"title" : "MongoDB Overview",
"description" : "MongoDB is no SQL database",
"by" : "蝴蝶教程",
"url" : "https://www.jc2182.com",
"tags" : [
"mongodb",
"database",
"NoSQL"
],
"likes" : 100
}
{
"_id" : ObjectId("5f474d67f4d867c5a4de618a"),
"title" : "NoSQL Database",
"description" : "NoSQL database doesn't have tables",
"by" : "蝴蝶教程",
"url" : "https://www.jc2182.com",
"tags" : [
"mongodb",
"database",
"NoSQL"
],
"likes" : 20,
"comments" : [
{
"user" : "user1",
"message" : "My first comment",
"dateCreated" : ISODate("2013-12-09T18:35:00Z"),
"like" : 0
}
]
}

MongoDB中的NOR

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}]})
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first_name不是“Radhika”或者last_name不是“Christopher”的文档 

db.empDetails.find( { $nor:[{"First_Name": "Radhika"}, {"Last_Name": "Christopher"} ] }).pretty();
{
"_id" : ObjectId("5f486da720f2c31cceb9e491"),
"First_Name" : "Fathima",
"Last_Name" : "Sheik",
"Age" : "24",
"e_mail" : "Fathima_Sheik.123@gmail.com",
"phone" : "9000054321"
}

MongoDB中的NOT

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}]})
以下示例将检索年龄不超过25岁的文档- 

db.empDetails.find( { "Age": { $not: { $gt: "25" } } } ).pretty();
{
"_id" : ObjectId("5f486da720f2c31cceb9e491"),
"First_Name" : "Fathima",
"Last_Name" : "Sheik",
"Age" : "24",
"e_mail" : "Fathima_Sheik.123@gmail.com",
"phone" : "9000054321"
}
以上是MongoDB 查询文档的全部内容。
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