Flask's ORM detailed instructions

ORM

ORM (Object Relational Mapping) is called object-relational mapping. It maps a class to a table in the database and maps attributes to columns in the database table. Each instance object corresponds to a row of data in the database table.

Install Flask-SQLAlchemy

pip install flask-sqlalchemy

create model

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config["SQLALCHEMY_DATABASE_URI"] = "sqlite:///test.db"

db = SQLAlchemy(app)


class Category(db.Model):
    __tablename__ = "t_category"
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(50))

db.create_all()

__tablename__The attribute defines the table name, which defaults to the class name, __tablename_zh__indicating the Chinese name of the table structure.
__table_desc__The attribute definition table describes the content.
db.create_all()Used to create all table structures.

Database Connectivity

SQLALCHEMY_DATABASE_URIDefine the database information that needs to be connected, and other commonly used database configurations:

database	connection address
MySQL	mysql+pymysql://username:password@host:3306/database name
SQL	mssql+pymssql://username:password@host:port/database name
Oracle	oracle+cx_oracle://username:password@host:1521/SID name
SQLite	sqlite:///filename

Create data type of Model field

field name	type	illustrate
Integer	int	Ordinary integer, usually 32 bits
SmallInteger	int	An integer with a small value range, usually 16 bits
BigInteger	int or long	Integer with unlimited precision
Float	float	floating point number
Double	float	double precision floating point
Numeric	decimal.Decimal	Fixed-point number (default decimal.Decimal, convert to float when asdecimal=False)
String	string	variable length string
Text	string	Programming strings, optimized for longer or unlimited length strings, for long text
Boolean	bool	Boolean value
Date	datetime.date	date only
Time	datetime.time	time only
DateTime	datetime.datetime	date and time
Interval	datetime.timedelta	time interval
Enum	Enum	enumerated type
ARRAY	array	array
PickType	any python object	Automatic serialization using Pickle
Unicode	unicode	variable-length Unicode string
UnicodeText	unicode	Variable-length Unicode strings, optimized for longer or unlimited-length strings
LargeBinary	binary	large binary byte data

Optional addition options for field descriptions

Attributes	illustrate
primary_key	primary key
default	Defaults
unique	Is it unique
nullable	Is it allowed to be empty
index	Whether to add as an index
autoincrement	self-increment
comment	note

one-to-many relationship

class Post(db.Model):
　　id = db.Column(db.Integer(),primary_key=True)
    title = db.Column(db.String(255))
　　text = db.Column(db.Text())
　　publish_date = db.Column(db.DateTime())
　　user_id = db.Column(db.Integer(),db.ForeignKey('user.id'))


class User(db.Model):
　　id = db.Column(db.Integer(),primary_key=True)
　　username = db.Column(db.String(255))
　　password = db.Column(db.String(255))
　　posts = db.relationship('Post',backref='user',lazy='dynamic')

注意:
1. The parameter passed to db.ForeignKey is a string used to represent the id column of the user table. If __tablename__ is used to customize the table name in the user table, you need to use the custom table name 2. "Multiple
" The side of "one" writes ForeignKey, and the side of "one" can be read and modified through the table name. (the backref of the side of "one"). The relationship can be on either side, usually on the "one" side.

lazy关键字说明：lazy 决定了 SQLAlchemy 什么时候从数据库中加载数据。
Optional values:
select: (default) When the properties of the object are read, all properties will be loaded.
dynamic: Returns a query object, and all data will be loaded only when the method of the object is executed. Such as: all()
joined: join operation is performed on the two associated tables, so as to obtain all related objects

many-to-many relationship

t_user_role = db.Table("t_user_role",
    db.Column("user_id", db.Integer, db.ForeignKey("t_user.id"), primary_key=True),
    db.Column("role_id", db.Integer, db.ForeignKey("t_role.id"), primary_key=True)
)


class User(db.Model):
    __tablename__ = "t_user"
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(15))
    roles = db.relationship("Role", backref="users", secondary=t_user_role)


class Role(db.Model):
    __tablename__ = "t_role"
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(15))

Add

u = User(name="张三")
db.session.add(u)

# 对于多对对关系
r1 = Role(name="Admin")
r2 = Role(name="User")
db.session.add(r1)
db.session.add(r2)
u.roles = [r1,r2]
db.session.add(u)

# 也可以使用这个方式
u.roles.append(r1)
u.roles.append(r2)
db.session.commit()

delete

c = Category.query.get(1)
db.session.delete(c)

batch deletion

# 方法一
posts = Posts.query.filter(User.user_id ==1).all()
for p in posts:
	db.session.delete(p)
db.session.commit()

#方法二
Posts.query.filter(User.user_id==1).delete(synchronize_session=False)
db.session.commit()

The above deletion operations are all logical deletions, so delete them carefully!

Revise

p = Posts.query.get(1)
p.title = "Python"
db.session.add(p)
db.session.commit()

Pending supplementary query operation. . .