[Mongo series] Practical practice of common operations

insert data

 > db.users.insert({"name" : "xiaomotong", "age" : 18})

> db.users.insert({name:"xiaozhu",age:15,hobby:"basketball",infos:{tall:190,height:70},school:"sh"})

> db.users.insertMany([{name:"xiaopang"},{name:"wangwu"}])

> db.users.insertMany([{name:"nancy", "age" :25, "hobby" : "study", "infos" : { "tall" : 175, "height" : 60 }, "school" : "hn" },{name:"job", "age" : 19, "hobby" : "basketball", "infos" : { "tall" : 170, "height" : 70 }, "school" : "nj" }])

• You can use insert, insertOne, and insertMany to insert different data, each takes what you need, of which insertMany is used to insert multiple pieces of data, of course, you can also insert 1 piece of data

mongodb has so many functions and methods that can be used in inserting data.

update data

 > db.users.find()
{ "_id" : ObjectId("61584aeeee74dfe04dac57e9"), "name" : "xiaomotong", "age" : 18 }
...

> db.users.update({name:"xiaomotong"},{$set:{name:"xiaokeai",age:25,hobby:"reading",infos:{tall:175,height:62},school:"cs"}})
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })

Use $set to indicate that the field needs to be updated

When querying data, we found that mongodb automatically added the _id field to our document, which is a primary key. If you don't set it yourself, mongodb adds it to us by default, which is a 24-bit uuid

Regarding the update method, the official website also provides these methods:

Find data

 > db.users.find({"infos.tall":{$gt:170}})
{ "_id" : ObjectId("61584aeeee74dfe04dac57e9"), "name" : "xiaokeai", "age" : 25, "hobby" : "reading", "infos" : { "tall" : 175, "height" : 62 }, "school" : "cs" }
{ "_id" : ObjectId("615a56d6bc6afecd2cff8f96"), "name" : "xiaozhu", "age" : 15, "hobby" : "basketball", "infos" : { "tall" : 190, "height" : 70 }, "school" : "sh" }
{ "_id" : ObjectId("615a5917d988690b07c69f66"), "name" : "nancy", "age" : 25, "hobby" : "study", "infos" : { "tall" : 175, "height" : 60 }, "school" : "hn" }

$gt here means greater than. I mentioned these operators in the last issue, so let's review them again

The above infos.tall belongs to a subquery, indicating that infos is an embedded document, and what needs to be searched is the tall field in the document. We can't add double quotation marks, because the system will recognize infos.tall as a field by default. In fact, this field cannot be found, so the query result cannot be obtained, and the following error is reported:

 > db.users.find({infos.tall:{$gt:170}})
2021-10-04T09:39:21.349+0800 E  QUERY    [js] uncaught exception: SyntaxError: missing : after property id :
@(shell):1:20

Query data in a more friendly way

 > db.users.find({"infos.tall":{$gte:180}}).pretty()
{
        "_id" : ObjectId("615a56d6bc6afecd2cff8f96"),
        "name" : "xiaozhu",
        "age" : 15,
        "hobby" : "basketball",
        "infos" : {
                "tall" : 190,
                "height" : 70
        },
        "school" : "sh"
}

Here db.users.find({"infos.tall":{$gte:180}}) is similar to the SQL statement of relational database: select * from users where "infos.tall" >= 180

For example, in a query, students whose height is 175 or 190.

Here db.users.find({"infos.tall":{$in:[190,175]}}) is similar to the relational database select * from users where "infos.tall" in (190,175)

Demonstrate a simple regular expression:

 > db.users.find({name:/^w/}).pretty()
{ "_id" : ObjectId("615a5856d988690b07c69f65"), "name" : "wangwu" }
> db.users.find({name:/g$/}).pretty()
{ "_id" : ObjectId("615a5856d988690b07c69f64"), "name" : "xiaopang" }

• Query the name field, match the results starting with w, and match wangwu
• Query the name resource, match the result ending with g, and match it out xiaotong

Here, when we query, /regular expression/, mongodb will automatically recognize and match and process according to the rules of regular expressions

We can also query for null

 > db.users.find({infos:null})
{ "_id" : ObjectId("615a5856d988690b07c69f64"), "name" : "xiaopang" }
{ "_id" : ObjectId("615a5856d988690b07c69f65"), "name" : "wangwu" }

> db.users.find({infos:{$exists:false}})
{ "_id" : ObjectId("615a5856d988690b07c69f64"), "name" : "xiaopang" }

The first method can be used if the query field is null, and the second method can be used if the query field does not exist

delete data

 > db.users.deleteOne({name:"wangwu"})
{ "acknowledged" : true, "deletedCount" : 1 }
> db.users.find({name:/^w/}).pretty()
>

Commonly used deletion methods are:

• db.users.deleteOne()
• db.users.deleteMany()
• db.users.remove()

Simple pagination query

 > use mytest
switched to db mytest
> db.users.find()
{ "_id" : ObjectId("61584aeeee74dfe04dac57e9"), "name" : "xiaokeai", "age" : 25, "hobby" : "reading", "infos" : { "tall" : 175, "height" : 62 }, "school" : "cs" }
{ "_id" : ObjectId("615a56d6bc6afecd2cff8f96"), "name" : "xiaozhu", "age" : 15, "hobby" : "basketball", "infos" : { "tall" : 190, "height" : 70 }, "school" : "sh" }
{ "_id" : ObjectId("615a5856d988690b07c69f64"), "name" : "xiaopang" }
{ "_id" : ObjectId("615a5917d988690b07c69f66"), "name" : "nancy", "age" : 25, "hobby" : "study", "infos" : { "tall" : 175, "height" : 60 }, "school" : "hn" }
{ "_id" : ObjectId("615a5917d988690b07c69f67"), "name" : "job", "age" : 19, "hobby" : "basketball", "infos" : { "tall" : 170, "height" : 70 }, "school" : "nj" }

> db.users.find().limit(2)
{ "_id" : ObjectId("61584aeeee74dfe04dac57e9"), "name" : "xiaokeai", "age" : 25, "hobby" : "reading", "infos" : { "tall" : 175, "height" : 62 }, "school" : "cs" }
{ "_id" : ObjectId("615a56d6bc6afecd2cff8f96"), "name" : "xiaozhu", "age" : 15, "hobby" : "basketball", "infos" : { "tall" : 190, "height" : 70 }, "school" : "sh" }

> db.users.find().skip(2).limit(2)
{ "_id" : ObjectId("615a5856d988690b07c69f64"), "name" : "xiaopang" }
{ "_id" : ObjectId("615a5917d988690b07c69f66"), "name" : "nancy", "age" : 25, "hobby" : "study", "infos" : { "tall" : 175, "height" : 60 }, "school" : "hn" }

• db.users.find() Query all data and print them out in the default order
• db.users.find().limit(2) From the previous results, the limit is 2
• db.users.find().skip(2).limit(2) From the previous result, offset by 2, and limit to take out 2

Next time, sort out and aggregate related content

Official first-hand information: https://docs.mongodb.com/manual/reference

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