[Introduction to MySQL] (5) Flask uses MySQL to store data

This article is based on MySQL 8.0.29 and Python 3.8.

1. Introduction to flask_sqlalchemy

Flask-SQLAlchemy is an extension that adds SQLAlchemy support to Flask applications. It is also a database framework that supports multiple database backgrounds. It strives to simplify the use of SQLAlchemy in Flask, providing useful defaults and additional helpers to more easily accomplish common tasks. No need to care about the details of SQL processing, and operate the database by calling methods. This is the Chinese documentation of flask_sqlalchemy .

2. 安装pymysql，sqlalchemy，flask_sqlalchemy

pip install pymysql sqlalchemy flask_sqlalchemy

3. Configure a simple Flask application

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = "mysql+pymysql://{}:{}@{}/{}?charset=utf8mb4" \
										.format('root','密码','x.x.x.x:3306','数据库名')
app.config['SQLALCHEMY_COMMIT_ON_TEARDOWN'] = True  # 每次请求结束后会自动提交数据库中的变动
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = True  # 事件系统跟踪修改
db = SQLAlchemy(app)  # 实例化数据库对象，它提供访问Flask-SQLAlchemy的所有功能

4. Define a class (corresponding to a table in the database)

class Myuser(db.Model):  # 所有模型的基类叫 db.Model，它存储在创建的SQLAlchemy实例上。
    #定义表名
    __tablename__ = 'myuser'
    #定义字段
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(64), unique=False)
    money = db.Column(db.Float, unique=False)

    #__repr__()方法显示一个可读字符串,用于调试、测试
    def __repr__(self):
        return '<Myuser id:{} name:{} money:{}>'.format(self.id,self.name,self.money)

Here's a simple example:

Common SQLalchemy column types

type name	python type	describe
Integer	int	regular integer, usually 32 bits
SmallInteger	int	Short integer, usually 16 bits
BigInteger	int or long	Unlimited precision shaping
Float	float	floating point number
Numeric	decimal.Decimal	Fixed number
String	str	variable length string
Text	str	Variable-length strings, good for large amounts of text
Unicode	unicode	Variable-length Unicode strings
Boolean	bool	Boolean
Date	datetime.date	date type
Time	datetime.time	time type
Interval	datetime.timedelta	time interval
Enum	str	character list
PickleType	any Python object	Automatic Pickle Serialization
LargeBinary	str	binary

Common SQLalchemy column options

optional parameters	describe
primary_key	If set to True, the primary key for this list
unique	If set to True, the column does not allow identical values
index	If set to True, create an index for this column, and the query efficiency will be higher
nullable	If set to True, the column is allowed to be empty. If set to False, the column does not allow null values
default	Define the default value for the column

5. Delete and create data tables

The following operations will affect all tables in the database:

 # 删除旧表：
db.drop_all() 
# 创建新表：
db.create_all()

6. Add, delete, modify and check the database

1. increase

user_A = Myuser(id=123, name='user_A', money=66.66)
user_B = Myuser(id=456, name='user_B', money=888.88)
#在将对象写入数据库之前，先将其添加到会话中（类似缓存）
# 插入单个对象
# db.session.add(user_A)
# 插入多个对象
db.session.add_all([user_A, user_B])
#会话提交到数据库后执行操作
db.session.commit()

result:
insert image description here

2. delete

db.session.delete(user_B)
db.session.commit()

result:
insert image description here

3. change

user_A.name = 'somebody'
user_A.money= 999
db.session.add(user_A)
db.session.commit()

result:
insert image description here

4. Check

Myuser.query.filter_by(id = 123).first()
Myuser.query.filter_by(name = 'somebody').all()

insert image description here
Commonly used SQLAlchemy query filters

filter	illustrate
filter()	Appends the filter to the original query, returning a new query
filter_by()	Appends the equality filter to the original query, returning a new query
limit	Limit the results returned by the original query to the specified value
offset()	Offset the results returned by the original query and return a new query
order_by()	Sort the original query results according to the specified conditions and return a new query
group_by()	Group the original query results according to the specified conditions and return a new query

Commonly used SQLAlchemy query executors

method	illustrate
all()	Returns all results of a query as a list
first()	Returns the first result of the query, or None if not found
first_or_404()	Return the first result of the query, if not found, return 404
get()	Returns the row corresponding to the specified primary key, or returns None if it does not exist
get_or_404()	Returns the row corresponding to the specified primary key, if it does not exist, returns 404
count()	Returns the number of query results
paginated()	Returns a Paginate object that contains results within the specified range