MongoDB super detailed nanny-level introductory tutorial!

1. Introduction to the database

SQL: Structured Query Language

2. Introduction to MongoDB

BSON: binary JSON

3. Set MongoDB as a system service

4. Basic operations of MongoDB

In MongoDB, neither database nor collection needs to be created manually. When we create a document, if the collection or database where the document is located does not exist, she will automatically create the database and collection!

• basic instructions

  • show dbs: show all current databases

    show database: Displays all current databases

  • use database name:Enterto the specified database (may not exist)

  • db: Indicates where we are currentlydatabase

  • show collections: show all the collections in our database

• CRUD operations

  • Insert document into database

    db..insert(doc): Insert a document into the collection

    Insert a new student object into the stus collection in the test database

    db.stus.insert({name: "Monkey King", age: 18, gender: "male"})

  • Query all documents in a collection

    db..find()

5. Install the graphical tool

6. Insert the document

db.collection.insert()

• Insert one or more documents into a collection
• When we insert a document into the collection, if the _id attribute is not specified for the document, the database will automatically add
  the _id attribute to the document, which is used as the unique identification of the document
• _id can be specified by yourself. If we specify it, the database will not be added. If you specify _id by yourself, it must also ensure uniqueness
  • db.collection.insertOne(): Insert a document object

• db.collection.insertMany(): Insert multiple document objects

db.stus.insert({
    
    name:"冉海锋",age:28,gender:"男"})
db.stus.find()db.stus.insert([
    {
    
    name:"沙和尚",age:36,gender:"男"},
    {
    
    name:"白骨精",age:16,gender:"女"},
    {
    
    name:"蜘蛛精",age:14,gender:"女"}
])

• $push: used to add a new element to the array

  db.user.update({username:"tangseng"},{$push:{"hobby.movies":"Interstellar"}})
  

• $addToSet: Adds a new element to the array (similar to adding to the set collection, if the element already exists in the array, the addition fails becausenot repeatable）

  db.user.update({
        
        username:"tangseng"},{
        
        $addToSet:{
        
        "hobby.movies":"Interstellar"}})
  

7. Querying documents

db.collection.find（）

• find() is used to query all eligible documents in the collection

• find() can receive an object as a condition parameter

  • { }: means all documents
  • {property:value}: The query property is a document with the specified value
  • The return value is aarray

• db.collection.findOne()

  • Used to query the first document in the collection that matches the criteria

  • returns a document

• db.stus.find({}).count(): Query the number of all results

db.stus.find({
    
    name:"冉海锋"})
db.stus.findOne({
    
    name:"冉海锋"})
db.stus.find({
    
    name:"冉海锋"})[0]
db.stus.find({
    
    }).length()

8. Modify the document

• db.collection.update(query condition, new object)
  • update() will by default use the new object toreplaceold object
  • update() will only modify one object by default

If you need to modify the specified attribute, instead of replacing, you need to use the "modification operator" to complete the modification

• $set: can be used to modify the specified property in the document
• $unset: Can be used to delete the specified attribute of the document

db.collection.updateMany(): Modify multiple eligible documents at the same time

db.collection.updateOne(): Modify a qualifying document

db.collection.replaceOne(): replace a qualifying document

• The attribute value of a MongoDB document can also be a document. When the attribute value of a document is a document, we call this document an embedded document.

• MongoDB supports querying directly through the properties of embedded documents. If you want to query embedded documents, you can use ==.form to match, and the attribute name must useQuotes ==, double quotes and single quotes can be

  db.user.find("hobby.movies"："hero")；
  

db.stus.find()

db.stus.update(
    {
    
    name:"沙和尚"},{
    
    age:28}
)

db.stus.update(
    {
    
    "_id" : ObjectId("5f86edc1048d21081bd45f3b")},
    {
    
    $set:{
    
            gender:"男",        address:"流沙河"    }}    )

db.stus.update(
    {
    
    "_id" : ObjectId("5f86edc1048d21081bd45f3b")},
    {
    
    $unset:{
    
            address:"流沙河"    }}    )

db.stus.updateMany(
    {
    
    "name" :"冉海锋"},
    {
    
    $set:{
    
        address:"高老庄"    }}    )

db.stus.find()

db.stus.update(
    {
    
    "name" :"冉海锋"},
    {
    
            $set:{
    
            address:"呵呵呵"        }    }, 
    {
    
                multi:true        }    )

db.stus.find()

9. Delete documents

• db.collection.remove（）
  • You can delete documents based on conditions, passing conditions in the same way as find()
  • Can delete all documents that meet the conditions, delete multiple by default
  • ifsecond parameterpass atrue, then only one
  • If only one { } is passed as a parameter, all documents in the collection will be removed
• db.collection.deleteOne（）
• db.collection.deleteMany（）
• db.collection.drop(): drop the collection (if the last collection is gone, the database is gone...)

db.stus.remove({
    
    age:28},true)
db.stus.remove({
    
    }) //性能差
db.stus.drop()
db.dropDatabase()

• Generally, the data in the database will not be deleted, so the delete method is rarely called. Generally, a field is added to the data to indicate whether the data is deleted.

10. Practice

//添加两万条数据的性能高，尽量少调用系统的方法
var arr=[];
for(var i=1;i<=20000;i++){
    
    
    arr.push({
    
    num:i});
}
db.user.insert(arr);

//查询numbers中num大于5000的文档
db.unmbers.find({
    
    num:{
    
    $gt:500}})

//查询numbers中num小于30的文档
db.unmbers.find({
    
    num:{
    
    $lt:500}})

//查询numbers中num大于40小于50的文档
db.numbers.find({
    
    num:{
    
    $gt:40,$lt:50}})

//查询numbers前10条的数据
db.numbers.find({
    
    num:{
    
    $lte:10}})

//limit()设置显示数据的上限
db.numbers.find().limit(10)

//查询numbers中第11条到20条的数据
	//skip()用于跳过指定数量的数据   skip( (页码-1)*每页显示的条数 ).limit(每页显示的条数)
	//MongoDB会自动调整limit()和skip()的位置
db.numbers.find().skip(10).limit(10)
db.numbers.find().limit(10).skip(10)

11. Relationships between documents

• one to one

  • couple

  • In MongoDB, this can be done viaembedded documentin the form of a one-to-one relationship

    db.WifeAndHusband.insert([
        {
            
            
            wife:"黄蓉",
            husband:{
            
            
                name:"郭靖"
            }
        },
        
        {
            
            
            wife:"潘金莲",
            husband:{
            
            
                name:"武大郎"
            }
        }
        
    ])
    

• one to many / many to one

  • One-to-many: parents and children, users and orders, articles and comments, also viaembedded documentway to map a one-to-many relationship (set the attribute of 1 to the field in the many)

    db.order.insert({
            
            
    	list:["watermelor"],
        user_id:ObjectId("5f87b1deda684b252c2fc7a5")
    })
    
    var user_id = db.users.findOne({
            
            username:"swk"})._id
    //查询孙悟空的订单
    db.order.find({
            
            user_id:user_id})
    

• many to many: categories and items, viaembedded documentThe way

  db.teacher.insert([
  	{name:"洪七公"},
      {name:"黄药师"},
      {name:"龟仙人"}
  ])
  
  db.stus.insert([
      {
          name:"郭靖",
          tech_ids:[
              ObjectId("5f87b4b6da684b252c2fc7a8"),
              ObjectId("5f87b4b6da684b252c2fc7a9")
          ]
      },   
      {
          name:"孙悟空",
          tech_ids:[
              ObjectId("5f87b4b6da684b252c2fc7a8"),
              ObjectId("5f87b4b6da684b252c2fc7a9"),
              ObjectId("5f87b4b6da684b252c2fc7aa")
          ]
      }
  ])
  

12. Practice

//查询工资小于1000或者大于2000的员工
db.emp.find( $or:[ {
    
    sal:{
    
    $lt:1000}},{
    
    sal:{
    
    $gt:2500}} ])

//为所有工资小于1000的增加400
db.emp.find({
    
    sal:{
    
    $lte:1000}},	{
    
    $inc:{
    
    $sal:400}})

13. sort and projection

• When find() queries documents, the default is to sort in ascending order according to the value of _id

• sort() can be used to specify the sorting rules of documents, need to pass aAttributesTo specify the collation, 1 means ascending order, -1 means descending order

  db.users.find({
        
        }).sort({
        
        sale:1})
  db.users.find({
        
        }).sort({
        
        sale:1,qq:1}) //先指定sale的升序 再qq的降序
  

• limit, skip, sort can be called in any order

• When querying, we can set the position of the second parameterProjection of query results

  db.users.find({
        
        },{
        
        sale:1})