[flask introduction series] installation and configuration of flask Sqlalchemy

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Preface

We usually use the drivers that connect to the database with writing sql The pain of , And it is very inconvenient for a large project to use database driver , So choose the right one orm The framework is necessary ！ this paper , I will write flask An extension of flask-sqlalchemy Installation and use of ！

Flask-SQLAlchemy Introduction of and selection of database driver

SQLAlchemy Is a relational database framework , It provides high-level ORM And the operation of the underlying native database .flask-sqlalchemy It's a simplification SQLAlchemy Operation of the flask Expand .
Speaking of this , A lot of people orm And database drivers are always confused ！ Now I'll draw a picture to understand ：

You can see that our database driver is responsible for our database from beginning to end mysql Connect ！
So use Flask-SQLAlchemy What kind of database driver do we use ！

stay python There are three kinds of database drivers commonly used in ：
1.MySQLdb
MySQLdb yes Python Connect MySQL One of the most popular drivers , Many frameworks are developed based on this library , Unfortunately, it Only support Python2.x, It is based on C Developed library , and Windows Platform compatibility is not friendly , It is not recommended to use , Instead of a derivative version of it .
2.mysqlclient
because MySQLdb In disrepair , And then there was its Fork edition mysqlclient, Fully compatible with MySQLdb,( Namely support python2）, Support at the same time Python3.x, yes Django ORM We rely on tools , If you want to use native SQL To manipulate the database , So we recommend this driver .
3.PyMySQL
PyMySQL Is pure Python The driver of implementation ,== Not as fast as MySQLdb, The biggest feature may be that its installation is not so tedious .== Support python2 and python3！

Many people, including myself, probably use it most often pymysql, But in our flask and django Use in pymysql Do additional operations , take django Come on , The default with MySQLdb, For compatibility python3, We use it MySQLdb The branch of , install mysqlclient, Therefore, no additional operation is required ！
If you want to use pymysql, We need to initialize the file in the project __init__.py Write the following code in ：

import pymysql
pymysql.install_as_MySQLdb()

about flask, This method is also used , There is another solution ：

app.config['SQLALCHEMY_DATABASE_URI']='mysql+pymysql://root:[email protected]:3306/flask'

That is, the initial agreement is not mysql, It is mysql+pymysql.

thus it can be seen ,pymysql Additional configuration is required , and mysqldb Do not apply python3, Obvious , Our choice of database driver should be consistent with django Same use mysqlclient, Although compared pymysql Less than , But the speed ratio pymysql fast ！

And in the flask Medium flask-mysqldb The extension of this connection database is based on mysqlclient Of , We finally use flask-mysqldb！

Flask-SQLAlchemy And flask-mysqldb Installation

pip install flask-sqlalchemy

If the connected database is mysql：

pip install flask-mysqldb

Be careful ： If you install directly flask-mysqldb Failure , Please first pip install mysqlclient install mysqlclient !

Flask-SQLAlchemy Configuration of

New in project directory settings.py file , Write the configuration in it , Load from the configuration file ！
Those who are not familiar with this area can go to my previous blog ：
【flask Introductory series 】Flask Object initialization parameters and Flask Loading method of project configuration

settings.py

# Set the url
SQLALCHEMY_DATABASE_URI = 'mysql://root:[email protected]:3306/flaskeatproject'

#  Dynamic tracking changes settings , If not set, it will only prompt warning , In other words, what you modify in the database will be models Medium sync 
SQLALCHEMY_TRACK_MODIFICATIONS = True

These two are enough for common configurations ！

app.py

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)

# From the configuration file settings Load the configuration 
app.config.from_pyfile('settings.py')

#  Instantiate model class objects , take app Load the database configuration in 
db = SQLAlchemy(app)

First, I will show a part here to understand , When explaining the usage later, it will be put into a private folder models In the middle ！

You can look at my project directory ：

other

frequently-used SQLAlchemy Field type

frequently-used SQLAlchemy Column options

frequently-used SQLAlchemy Relational options

Conclusion

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