MongoDB study notes (five)-addition, deletion, modification, and check

This article will introduce the related operations of adding, deleting, modifying and checking the MongoDB database. For details, please refer to the official manual: https://docs.mongodb.com/manual/

This page also provides MongoDB Web Shell , which can be used to simulate the database environment online to facilitate learning.

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increase

db.collection.insert()

-Insert one or more documents into the collection

When we insert a document into the collection, if the _id attribute is not specified for the document, the database will automatically add _id to the document, which is used as the unique identifier of the document.

• Insert one

db.c1.insert({name:"tom", age:"18", gender:"男"})

• Insert multiple

db.c1.insert([
    {name:"tom", age:"18", gender:"男"},
    {name:"jenney", age:"16", gender:"女"},
    {name:"klay", age:"20", gender:"男"}
])

• _id can be specified by yourself, the database will not be automatically added, and you must specify its own uniqueness

db.c1.insert({_id:"hello", name:"tom", age:"18", gender:"男"})

• ObjectId() can be used to generate id, generated by timestamp and machine code

ObjectId()

db.collection.insertOne()

-Insert a document object

Both insertOne() and insertMany() can be regarded as the split of insert(), which is a new function added after version 3.2, in order to standardize the operation.

db.c1.insertOne({name:"tom", age:"18", gender:"男"})

db.collection.insertMany()

-Insert multiple document objects

db.c1.insertMany([
    {name:"tom", age:"18", gender:"男"},
    {name:"jenney", age:"16", gender:"女"},
    {name:"klay", age:"20", gender:"男"}
])

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check

db.collection.find()

-find() is used to query all documents in the collection that meet the conditions , and the return is an array

• Query all documents in the collection

db.c1.find() 
db.c1.find({}) 

• find() can receive an object as a condition parameter, and the query attribute is a document with the specified value {field:value}

db.c1.find({age:"18"}) 

• The collection of query results

db.c1.find({_id:"hello", name:"wyc"})

• The first file of the query result

db.c1.find({age:"18"})[1]

• The name of the first file in the query result

db.c1.find({age:"18"})[1].name

• The number of all query results

db.collection.find({age:"18"}).count()

db.collection.findOne()

-Used to query the first document that meets the conditions in the collection, and returns a document object

db.c1.findOne({age:"18"})

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change

db.collection.update()

• update(query condition, new object) will replace the old object with the new object, only one will be modified by default

db.c1.update({name:"tom"},{age:28})

• If you need to modify rather than replace the specified attribute, you need to use the "modification operator" to complete the modification

    $set can be used to modify the specified attributes in the document
    $unset can be used to delete the specified attributes of the document
    ...

db.c1.update(
    {"_id":"123"},
    {$set:{
        gender:"男"
        address:"北京"
        }}
)

• update() will only modify one by default. To modify multiple, add another parameter {multi: true}

db.c1.update(
    {"_id":"123"},
    {$set:{
        gender:"男"
        address:"北京"
        },
    {multi:true}
)

db.collection.updateMany()

 -Modify multiple eligible documents at the same time

db.collection.updateOne()

 -Modify a document that meets the conditions

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delete

db.collection.remove()

-remove can delete documents based on conditions. The method of passing conditions is the same as find(). Delete all documents that meet the conditions

• Delete the specified document

db.c1.remove({age:28})

• If the second parameter of remove() is passed a true, only one will be deleted

db.c1.remove({age:28}, true)

• Report an error if you don’t pass the conference

db.c1.remove()

• Only pass an empty parameter {}, which is equivalent to emptying the collection (delete one by one, poor performance), show still exists after deletion

db.c1.remove({})
show collections

db.collection.deleteOne()

-Delete a document

db.c1.deleteOne({age:28})

db.collection.deleteMany()

-Delete all documents

db.c1.deleteMany({age:28})

db.collection.drop()

-Delete the entire collection, show does not exist after deletion

db.c1.drop()
show collections

db.dropDatabase() 

-Delete the entire database

use testdb
db.dropDatabase() 

isDel field

-Add a specified field such as isDel to represent whether the document is used, so there is no need to delete the data completely, which is convenient for maintenance