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。
The find() Method
要从 MongoDB 集合中查询数据，你需要使用 MongoDB 的 find() 方法。
Example
假设我们创建了一个名为 mycol 的集合，如下所示 −
> use sampleDB
switched to db sampleDB
> db.createCollection("mycol")
{ "ok" : 1 }
>并使用 insert() 方法在其中插入了 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 } ] }
>The pretty() Method
要以格式化方式显示结果，可以使用 pretty() 方法。
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。
> 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。
Example
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 Where Clause Equivalents in MongoDB
要根据某个条件查询文档，可以使用以下操作。
Operation |
Syntax |
Example |
RDBMS Equivalent |
Equality |
{<key>:{$eg;<value>}} |
db.mycol.find({"by":"tutorials point"}).pretty() |
其中 by = 'tutorials point' |
Less Than |
{<key>:{$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":{$in:["Raj", "Ram", "Raghu"]}}).pretty() |
其中 name 可匹配 :["Raj", "Ram", "Raghu"] 中的任何一个值 |
不在数组中的值 |
{<key>:{$nin:<value>}} |
db.mycol.find({"name":{$nin:["Ramu", "Raghav"]}}).pretty() |
当 name 值不在数组 :["Ramu", "Raghav"] 中，或根本不存在时 |
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 −
>db.mycol.find({ $and: [ {<key1>:<value1>}, { <key2>:<value2>} ] })Example
以下示例将显示所有由“教程点”编写的教程，其标题为“MongoDB 概述”。
> db.mycol.find({$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。
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 −
>db.mycol.find(
{
$or: [
{key1: value1}, {key2:value2}
]
}
).pretty()Example
以下示例将显示所有由“教程点”编写的教程，或其标题为“MongoDB 概述”的教程。
>db.mycol.find({$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')'
>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 −
>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 −
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
> 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"
}