In front of the word

This article will introduce in detail MongoDB Database on the addition, deletion and modification of documents

Inserted into the document

To insert data into  MongoDB Collection , Need to use MongoDB Of  insert() or save() Method , also insertOne() or insertMany() Method

【insert()】

insert() The basic syntax of the command is as follows

db.COLLECTION_NAME.insert(document)

In the inserted document , If you don't specify _id Parameters , that MongoDB A unique... Will be assigned to this document ObjectId._id Unique for each document in the collection 12 Hexadecimal number of bytes

_id, Also known as ObjectId It's a 12 Bytes of BSON Type string . Represent... In byte order :

4 byte :UNIX Time stamp

3 byte : Said to run MongoDB Machine

2 byte : Indicates that this _id The process of

3 byte : The value generated by a counter starting with a random number

If the collection does not exist in the database , be MongoDB This collection will be created , Then insert the document into the collection

To insert multiple documents in a single query , Can be in insert() The command passes an array of documents

[ Be careful ] Use insert() When inserting multiple documents , It's easy to have problems . Best use insertMany() Method insert

have access to js grammar , Insert multiple documents

【save()】

Insert documents can also be used db.post.save(document). If not specified in the document _id, that save() The method will be the same as insert() Method is the same as automatic allocation ID Value . If specified _id, It will be save() Method contains _id All data of the document .

in other words save() Methods and insert() The difference in method is ,save() Methods can be duplicated or modified , and insert() Method can not

db.post.save(document)

【insertOne()】

Use db.collection.insertOne() Method to insert a single document into a collection

【insertMany()】

Use db.collection.insertMany() Method to insert multiple documents into a collection

Query the document

【find()】

From you to MongoDB Set query data , Need to use MongoDB Of find() Method , By default, the first... In the result is returned 20 Documents , Input "it" Show the next 20 Documents .

find() The basic syntax of the command is as follows :

db.COLLECTION_NAME.find(document)

find() Method will display all documents in an unstructured way

You can limit the query conditions

Can pass find To specify the returned key , The value is 1 or true Indicates that the key is displayed , The value is 0 or false Indicates that the key is not displayed

find() Under the method count() Method to display the number of eligible documents

【findOne()】

findOne() Method returns only one document , This is the first document to be added

【 Comparison operator 】

 Less than {<key>:{$lt:<value>}}
Less than or equal to {<key>:{$lte:<value>}}
Greater than {<key>:{$gt:<value>}}
Greater than or equal to {<key>:{$gte:<value>}}
It's not equal to {<key>:{$ne:<value>}}
be equal to {<key>:{$eq:<value>}}

obtain x Less than 2 Value

obtain x Greater than or equal to 2 Value

obtain x It's not equal to 2 Value

【 Logical operators 】

You can use logical operators $and、$or To express and 、 or

{ $and: [ { <expression1> }, { <expression2> } , ... , { <expressionN> } ] }
{ $nor: [ { <expression1> }, { <expression2> }, ... { <expressionN> } ] }

【 Regular expressions 】

Document queries can use regular expressions , But only string type data is supported

【$where】

$where Operators are powerful and flexible , It can use any JavaScript As part of the query , contain JavaScript The string of the expression or JavaScript function

Use string

Using functions

Limit and skip

【limit()】

If you need to MongoDB Read a specified number of data records , have access to MongoDB Of Limit Method ,limit() Method accepts a numeric parameter , This parameter specifies from MongoDB Number of records read in

By default, the first... In the result is returned 20 Documents , Input "it" Show the next 20 Documents

If not specified limit() The parameters in the method display all the data in the collection

db.COLLECTION_NAME.find().limit(NUMBER)

【skip()】

have access to skip() Method to skip a specified amount of data ,skip Method also accepts a numeric parameter as the number of records to skip

db.COLLECTION_NAME.find().skip(NUMBER)

Sort

【sort()】

stay MongoDB Use in sort() Method to sort the data ,sort() Method can be used to specify the sorting field by parameter , And use 1 and -1 To specify how to sort , among 1 Arrange... In ascending order , and -1 It's for descending order

db.COLLECTION_NAME.find().sort({KEY:1})

Update the document

MongoDB Use update() or save() Method to update the document in the collection

【update()】

update() Method to update an existing document . The syntax is as follows :

db.collection.update(<query>,<update>,{upsert:<boolean>, multi: <boolean>,writeConcern:<document>})
query : update Query criteria for , similar sql update In the query where hinder 
update : update Object and some updated operators ( Such as $,$inc...) etc. , It can also be understood as sql update In the query set hinder
upsert : Optional , This parameter means , If it doesn't exist update The record of , Whether insert objNew,true Insert for , The default is false, Do not insert
multi : Optional ,mongodb The default is false, Update only the first record found , If this parameter is zero true, According to the conditions to find out all the records updated
writeConcern : Optional , The level at which an exception is thrown

[ Be careful ] After testing ,upsert Parameter cannot be set to true perhaps false, You can insert new fields

mongodb Only the first record found is updated by default , take x:1, Updated to x:10

Pay special attention to , If not used $set, Replace the content of the document with x:10

Update all records , take x:10, Updated to x:1

mongodb Only the first record found by update is added by default , take x:1 The record of , add to z:1

Will find the x:2 All the records of , add to z:2

【save()】

save() Method to insert or update a document , If the document in the parameter _id And what exists in the set _id All different , The insert ; If the same , Update

Delete the document

MongoDB remove() Function is used to remove data from a collection

【remove()】

By default ,mongodb Delete all eligible documents

db.collection.remove(<query>,{justOne: <boolean>, writeConcern: <document>})
query : Conditions for deleted documents .
justOne : ( Optional ) If it is set to true or 1, Only one document is deleted .
writeConcern :( Optional ) The level at which an exception is thrown .

Delete only the first document that meets the criteria

Delete all eligible documents

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