Mongodb getting started Tutorial Part 04 mongodb client

This article introduces MongoDB Client tools mongo Use .

mongo shell

mongo shell Is a connection MongoDB The interactive JavaScript Interface .mongo shell Can be used to operate MongoDB Data in , You can also perform some management tasks .

mongo shell Be similar to MySQL Database client mysql,PostgreSQL client psql, perhaps Oracle In the database SQL*Plus Tools .

Be careful ,MongoDB v5.0 It is abandoned by default at the beginning MongoDB Installed together mongo shell, Recommend using the new mongsh.

In the use of mongo shell Before , We need to Download and install This tool .

After installation , Enter the following command on the command line ：

mongosh

mongo shell Will automatically connect to the local （localhosr） Default port （27017） Upper MongoDB service .

mongo shell That is, it can be used as a fully functional JavaScript Interpreter , Can also be used as a MongoDB Client tools .

JavaScript Interpreter

mongo shell It's a fully functional one JavaScript Interpreter , So we can use it to execute JavaScript Code . for example ：

> Math.max(10,20,30);
30

mongo shell Allow to enter cross line commands , When we enter enter, it will detect JavaScript Whether the statement is complete . If the statement is incomplete , We can continue to enter on the next line ：

> function add(a, b) {
    
... return a + b;
... }
> add(10,20);
30

Input console.clear() The command can clear the screen ：

console.clear()

MongoDB client

mongo shell It's a MongoDB client . By default , It will connect to the local MongoDB In service test database , And set the database connection as a global variable db.

db Variables can be used to view the current database ：

> db
test

except JavaScript Beyond grammar ,mongosh It also provides a lot of convenience for us to communicate with MongoDB Commands exchanged by the database server . for example ,shows dbs The command can list all databases in the service ：

test> show dbs
admin        41 kB
config     73.7 kB
local      81.9 kB

The above output shows 3 A database .

If you want to switch the current database , have access to use command . for example , The following command can switch the current database to bookdb database ：

test> use bookdb
switched to db bookdb

Be careful , We can switch to a nonexistent database . here , When we first saved data ,MongoDB This database will be created automatically .

After executing the above order , Variable db The value of is bookdb：

> db
bookdb

here , We can use variables db Access database bookdb The set in books：

> db.books
bookdb.books

Basic CRUD operation

Let's demonstrate how to create （Create）、 Read （Read）、 to update （Update） And delete （Delete） file . These operations are also known as CRUD.

This article only covers simple CRUD operation , We will learn more about CRUD operation .

create documents

If you want to create a new document in the collection , have access to insertOne() Method .

The following command is set books Added a new document （ A new book ）：

db.books.insertOne({
    
   title: "SQL Programming idea ",
   published_year: 2021
})

The output is as follows ：

{
    
        "acknowledged" : true,
        "insertedId" : ObjectId("62bb0962874071c64b1f9b7b")
}

When we enter enter ,mongo shell Will send the command to MongoDB The server . If the command is valid ,MongoDB Will insert the document and return the result .

In the example above , The return object contains two keys ：acknowledged and insertedId.insertedId The value of is the document _id Field .

If we add documents without specifying _id Field ,MongoDB A unique... Is automatically assigned to the document ObjectId As _id Value of field .

MongoDB Use _id Fields uniquely identify documents in the collection .

Search for documents

If you want to find documents in the collection , have access to findOne() Method . for example ：

db.books.findOne()

The output is as follows ;

{
    
  _id: ObjectId("62bb0962874071c64b1f9b7b"),
  title: 'SQL Programming idea ',
  published_year: 2021
}

pretty() Method can format and display the output results , for example ：

db.books.find().pretty()

{
    
        "_id" : ObjectId("62bb0962874071c64b1f9b7b"),
        "title" : "SQL Programming idea ",
        "published_year" : 2021
}

Update the document

If you want to update the content of a document , have access to updateOne() Method . This method requires at least two parameters ：

• The first parameter specifies the document to be updated .
• The second parameter specifies the content of the update operation .

The following example updates the title “SQL Programming idea ” The document published_year Field ：

db.books.updateOne(
	{
     title: "SQL Programming idea "}, 
	{
     $set: {
     published_year: 2022 }}
)

among , The first parameter indicates that the update title is “SQL Programming idea ” The first document of . The second parameter uses $set Operators update fields published_year Value . The results are as follows ：

{
    
  acknowledged: true,
  insertedId: null,
  matchedCount: 1,
  modifiedCount: 1,
  upsertedCount: 0
}

Delete the document

If you want to delete a document in the collection , have access to deleteOne() Method . The method contains a parameter , Used to specify the document to delete .

The following example uses deleteOne() Method to delete a collection books The title is “SQL Programming idea ” The first document of ：

db.books.deleteOne({
    title: "SQL Programming idea "});

The output is as follows ：

{
    
    "acknowledged": true,
    "deletedCount": 1
}

Returns... In the result deletedCount Indicates that a document has been successfully deleted .

If you want to view all collections in the current database , have access to show collections command ：

show collections

books

database bookdb Currently, there is only one set in .