MongoDB--How to use the database

MongoDB?

• MongoDB is a database based on distributed file storage. Written in C++ language. Designed to provide scalable high-performance data storage solutions for WEB applications.
• MongoDB stores data as a document, and the data structure is 键值对(key=>value)composed of.
• The MongoDB document is similar JSON 对象. The field value can include other documents, arrays and document arrays.
• MongoDB is a product between relational and non-relational databases. It is the most versatile and most like relational database among non-relational databases.

1. MongoDB terminology

SQL terminology	Explanation	MongoDB terminology	Explanation
database	database	database	database
table	table	collection	set
row	Row	document	Documentation
column	Field	field	area

.和$Have a special meaning, can only be used in a specific environment

2.MongoDB data type

type of data	description
String	String. Data types commonly used to store data. In MongoDB, UTF-8 encoded strings are legal.
Integer	Integer value. Used to store values. According to the server you use, it can be classified as 32-bit or 64-bit.
Boolean	Boolean value. Used to store boolean values ​​(true/false).
Double	Double-precision floating-point value. Used to store floating point values.
Min/Max keys	Compare a value with the lowest and highest value of the BSON (binary JSON) element.
Array	Used to store an array or list or multiple values ​​as a key.
Timestamp	Timestamp. Record the specific time when the document was modified or added.
Object	Used for embedded documents.
Null	Used to create null values.
Symbol	symbol. This data type is basically equivalent to the string type, but the difference is that it is generally used in languages ​​that use special symbol types.
Date	Date time. Use UNIX time format to store the current date or time. You can specify your own date and time: create a Date object and pass in the year, month, and day information.
Object ID	Object ID. ID used to create the document
Binary Data	Binary data. Used to store binary data.
Code	Type of code. Used to store JavaScript code in the document.
Regular expression	Regular expression type. Used to store regular expressions.

2. MongoDB user authentication login

In the cmd environment:

1. Set user name and password
   

use admin
db.create(
{
	user:'root',
	pwd:'123456',
	roles:[{
		role:'userAdminAnyDatabase', 
		db:'admin'
	}]
})

2. User authentication login

（1）

mongo --port 27017 -u 'root' -p '123456' --authenticationDatabase 'admin'

（2）

mongo --port 27017
use admin
db.auth('root','123456)

3. MongoDB statement

1. Create a database:use 数据库名;
2. Delete the database:db.dropaDtabase()
3. Create a collection:db.createCollection(name,options)
4. Delete collection:db.集合名.drop()
5. Insert document:
   db.集合名.insertOne/insertMany(document)
db.集合名.save(document)
6. Update documentation:db.集合名.update()
7. Query documents:db.集合名.find({条件})
8. Delete document:db.集合名.remove({条件})

4. MongoDB index

Index: It is essentially a sorted list, which stores the value of the index and the physical address of the data containing this value.
Function: It can speed up data retrieval, sorting, and grouping, and reduce disk I/O

Generally follow: primary/foreign key columns, columns for comparison, columns for range search, columns that are frequently arranged/columns for grouping

Statement:

1. Create index:db.集合名.createIndex({索引名:1/-1})
2. View index:
   db.集合名.getIndexes()
db.集合名.find({条件}).explain()
3. Delete index:db.集合名.dropIndex({条件})

Types of:

1. Compound index
2. Hash index
3. Multi-key index
4. Unique index
5. Sparse index
6. TTL index

4. MongoDB aggregate query

db.集合名.aggregate([{$group:{_id:'$artist'，著作和:{$sum:1}}}])

$sum $svg
$min $max
$push $addToSet
$first $last

Stage operator:

1. $project Modify the document structure, rename, add, delete content in the document

//    1:显示    0：不显示
db.books.aggregate([{$project:{_id:0,title:1,price:1}}])

2. $match Filter documents

//    类似与find()
db.books.aggregate([{$match:{
   
   'price':{$gte:150}}}])

3. $group Group the documents in the collection, which can be used for statistical results

//    1:升序      
db.books.aggregate([{$group:{_id：'$artist',数量：{
   
   '$sum':1}}}])

4. $sort Sort (ascending)

//    1:升序      
db.books.aggregate([{$sort:{
   
   'price':1}}])

5. $limit Limit the number of documents returned

db.books.aggregate([{$limit:2}])

6. $skip Skip the specified number of documents and return the remaining documents

7. $unwind Divide the documents of the array type in the document into multiple pieces, and the media contains one value in the array according to the document

db.classes.aggregate([{$match:{
   
   'classname':'class1'}},{$unwind:'$student'}])