02 mongodb data types, important concepts and common shell instructions

Catalog ： The basic chapter （ Can solve the problem of 80 The problem of ）
01 MongoDB Overview 、 Application scenarios 、 Download mode 、 Connection mode and development history, etc

02 MongoDB data type 、 Key concepts and shell Commonly used instructions

03 MongoDB Various additions to documents 、 to update 、 Delete operation summary

04 MongoDB Various query operations And summary of aggregation operations

05 MongoDB Summarize the various operations of the column

python3 operation MongoDB Various cases of

One . mongo data type

data type	describe
String	character string . Data types commonly used to store data . stay MongoDB in ,UTF-8 The encoded string is legal .
Integer	Integer values . For storing values . Depending on which server you use , Can be divided into 32 Bit or 64 position .
Boolean	Boolean value . Used to store Boolean values （ really / false ）.
Double	Double precision floating point value . Used to store floating point values .
Min/Max keys	Combine a value with BSON（ The binary JSON） The ratio of the lowest value of an element to the highest value .
Array	Used to store an array or list or values as a key .
Timestamp	Time stamp . Record when the document was modified or added .
Object	Used for embedded documents .
Null	Used to create a null value .
Symbol	Symbol . This data type is basically the same as the string type , But the difference is , It is commonly used in languages with special symbol types .
Date	Date time . use UNIX Time format to store the current date or time . You can specify your own time and date ： establish Date object , Incoming year, month and day information .
Object ID	object ID. For creating documents ID.
Binary Data	binary data . Used to store binary data .
Code	Code type . Used for storage in documents JavaScript Code .
Regular expression	Regular expression type . Used to store regular expressions .

1.1 Several important data types :

ObjectId: It's like a unique primary key , It can be quickly generated and sorted , contain 12 bytes, The meaning is ：

• front 4 Four bytes means create unix Time stamp , GMT UTC Time , It's later than Beijing time 8 Hours
• Next 3 Bytes is the machine identity code
• The two bytes immediately followed by the process id form PID
• The last three bytes are random Numbers
  

character string : BSON All strings are UTF-8 code .

Time stamp : BSON The timestamp type is primarily used MongoDB For internal use . In most cases application development , have access to BSON The date type .

The date type : Represents the current distance Unix A new era （1970 year 1 month 1 Japan ） Millisecond count . Date types are signed , Negative said 1970 Year before date .

Two . Important concepts

2.1 mongo And sql Comparison of terms

SQL The term / Concept	MongoDB The term / Concept	explain / explain
database	database	database
table	collection	Database table / aggregate
row	document	Data record row / file
column	field	Data field / Domain
index	index	Indexes
table joins		Table joins ,MongoDB I won't support it
primary key	primary key	Primary key ,MongoDB Automatically put _id Field sets the primary key

2.2 MongoDB Retained databases

Some database names are reserved , You can directly access these databases for special purposes .

admin： From a rights perspective , This is a "root" database . Add a user to the database , This user automatically inherits permissions for all databases . Certain server-side commands can only be run from this database , Such as listing all the databases or shutting down the server .
local: This data will never be copied , Can be used to store any collection limited to a single local server
config: When Mongo Used for sharding Settings ,config The database is used internally , Used to save information about sharding .

2.3 file (document)

A document is a set of key values (key-value) Yes ( namely BSON).MongoDB The document does not need to be set to the same field , And the same fields do not require the same data type , This is very different from a relational database , It's also MongoDB Very prominent characteristics .

Be careful ：
Document data structure and JSON Is essentially the same .
All data stored in the collection is BSON Format .
BSON It's a kind of similarity JSON The binary form of storage format , yes Binary JSON For short .

2.4 aggregate （collection）

The collection is MongoDB The document set , Be similar to RDBMS （ Relational database management system ：Relational Database Management System) The table in .

The collection exists in the database , Sets have no fixed structure , This means that you can insert different formats and types of data into collections , But usually the data that we insert into a collection has a certain degree of relevance .

Valid collection name

• The collection name cannot be an empty string "".
• The collection name cannot contain \0 character （ Null character ), This character represents the end of the collection name .
• The set name cannot be "system." start , This is the reserved prefix for the system set .
• User-created collection names cannot contain reserved characters . Some drivers do support inclusion in the collection name , This is because some system-generated collections contain this character . Unless you want to access a collection created by this system , Otherwise, don't put it in your name $.

2.5 Several important executables

mongod： Start the executable of the database instance , As a whole MongoDB The core file in , Responsible for database creation 、 Delete and other management work , Running on the server side , Listen for connection requests from clients .

mongo process ： It's a relationship with mongod Processes interact with each other JavaScript Shell process , It provides some interactive interface functions for the system administrator to manage the database .

mongodump： Export data to BSON File format , Backup database , At the same time, these dump File rebuild database . Use mongodump -help You can view the supported directives .

mongorestore： Restore backup files .

mongoexport： Export data to json or csv File format .

mongoimport： take json or csv Import the file of format into mongo.

mongos： Process files used in sharding , All query operations on the application side will be analyzed with it first , Then locate the query on a partition , Its monitoring function is similar to mongod The monitoring function of is similar to .

mongofiles：mongofiles Provides an operation MongoDB Distributed file storage GridFS Command line interface of the system .

mongostat： Show the currently running mongod or mongos Instance status tool , amount to unix/linux Of vmstat, But the data it provides is only related to the running mongod or mongos Examples related to .

mongotop： Provides an analysis MongoDB Instance time tracking method on read / write data .

3、 ... and . Commonly used shell Instructions

mongo Get into mongo Environmental Science ;

db.help(): Display instruction method and meaning ;
show dbs : Displays a list of all data .( perhaps show databases Instructions );
use Database name : Database does not exist , Then create the database , Otherwise switch to the specified database ;
db.dropDatabase() : Delete database （ First use Database name Enter the database to delete ）;
show collections : Show collection name （ Or use show tables command ）
db.createCollection("user_demo") : Create set user_demo;
db.user_demo.drop() : Delete the collection user_demo.

Be careful : Create set : db.createCollection(name, options),
name Is the name of the collection to be created ;
options Is an optional parameter , Specifies the options for memory size and index , The parameters are as follows :

capped： Boolean type , Optional ） If true, Creates a fixed collection . A fixed set is a set with a fixed size , When it reaches its maximum , It automatically overwrites the earliest document .
When the value is true when , Must specify size Parameters .
autoIndexId：3.2 This parameter is no longer supported .（ Optional ） If true, Automatically in _id Field creation index . The default is false.
size：（ Optional ） Specifies a maximum value for a fixed set , That is, the number of bytes .
If capped by true, You also need to specify this field .
max：（ Optional ） Specifies the maximum number of documents to contain in a fixed collection .