Flask-SQLAlchemy

Flask-SQLAlchemy

# SQLAlchemy是一个基于Python实现的ORM框架,跟web框架无关,独立的
# django的orm,sqlalchemy（big and heavy）,peewee（小而轻）
# 异步orm框架：GINO
# PythonThere is no particularly good microservice framework in the world：nameko
# java：dubbo（阿里开源）,springcloud
# go：grpc,go-zero,go-micro

pip install flask-sqlalchemy

1、基本配置

配置选项	说明
SQLALCHEMY_DATABASE_URI	连接数据库.示例：mysql://username:[email protected]/post/db?charset=utf-8
SQLALCHEMY_BINDS	一个将会绑定多种数据库的字典. 更多详细信息请看官文 绑定多种数据库.
SQLALCHEMY_ECHO	调试设置为true
SQLALCHEMY_POOL_SIZE	数据库池的大小,默认值为5.
SQLALCHEMY_POOL_TIMEOUT	连接超时时间
SQLALCHEMY_POOL_RECYCLE	自动回收连接的秒数.
SQLALCHEMY_MAX_OVERFLOW	控制在连接池达到最大值后可以创建的连接数.当这些额外的 连接回收到连接池后将会被断开和抛弃.
SQLALCHEMY_TRACK_MODIFICATIONS	如果设置成 True (默认情况),Flask-SQLAlchemy 将会追踪对象的修改并且发送信号.这需要额外的内存, 如果不必要的可以禁用它.

操作数据库需要先创建一个db对象,通常写在exts.py文件里.

from flask_sqlalchemy import SQLAlchemy

db = SQLAlchemy()

flask项目一般将数据库配置写入configs.py文件里面,配置在创建引擎前需写好,不要在程序运行时修改配置,如下.

HOST = '127.0.0.1'
PORT = '3306'
DATABASE = 'flask1'
USERNAME = 'root'
PASSWORD = '123456'

DB_URI = "mysql+pymysql://{username}:{password}@{host}:{port}/{db}?charset=utf8".format(username=USERNAME,password=PASSWORD, host=HOST,port=PORT, db=DATABASE)

SQLALCHEMY_DATABASE_URI = DB_URI
SQLALCHEMY_TRACK_MODIFICATIONS = False
SQLALCHEMY_ECHO = True

写完数据库配置后需要和app绑定,app.py文件里写flask应用的创建和蓝图的注册等等,如下：

from flask import Flask
import configs
from exts import db

app = Flask(__name__)
# 加载配置文件
app.config.from_object(configs)
# db绑定app
db.init_app(app)

2、SQLAlchemy的数据类型

The image below shows the most commonly used onesSQLAlchemy列的类型：

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The image below shows the most commonly used onesSQLAlchemy列选项：

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Flask-SQLAlchemy 要求每个模型都要定义主键,这一列经常命名为 id.

下图展示了SQLAlchemyProvided filter and query functions：

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3、示例

# -*- coding:utf-8 -*-
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
 
app = Flask(__name__)
# url的格式为：数据库的协议：//用户名：密码@ip地址：端口号（默认可以不写）/数据库名
app.config["SQLALCHEMY_DATABASE_URI"] = "mysql://root:[email protected]/first_flask"
# 动态追踪数据库的修改. 性能不好. 且未来版本中会移除. 目前只是为了解决控制台的提示才写的
app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = False
# Create an operation object for the database
db = SQLAlchemy(app)
 
 
class Role(db.Model):
 
    __tablename__ = "roles"
    id = db.Column(db.Integer,primary_key=True)
    name = db.Column(db.String(16),unique=True)
    # 给Role类创建一个uses属性,关联users表.
    # backrefis the reverse to giveUser类创建一个role属性,关联roles表.这是flask特殊的属性.
    users = db.relationship('User',backref="role")
    # 相当于__str__方法.
    def __repr__(self):
        return "Role: %s %s" % (self.id,self.name)
 
 
class User(db.Model):
    # Redefine a name for the table,The default name is lowercase of the class name,For example, the default table name of this class is user.
    __tablename__ = "users"
    id = db.Column(db.Integer,primary_key=True)
    name = db.Column(db.String(16),unique=True)
    email = db.Column(db.String(32),unique=True)
    password = db.Column(db.String(16))
    # 创建一个外键,和django不一样.flaskYou need to specify a specific field to create a foreign key,Foreign keys cannot be created based on class names
    role_id = db.Column(db.Integer,db.ForeignKey("roles.id"))
 
    def __repr__(self):
        return "User: %s %s %s %s" % (self.id,self.name,self.password,self.role_id)
 
 
@app.route('/')
def hello_world():
    return 'Hello World!'
 
if __name__ == '__main__':
    # 删除所有的表
    db.drop_all()
    # 创建表
    db.create_all()
 
    ro1 = Role(name = "admin")
    # 先将ro1对象添加到会话中,可以回滚.
    db.session.add(ro1)
    
    ''' 在执行 db.session.commit() Error submitting to the database,A database rollback needs to be performed,Ensure that subsequent operations are normal. try: . . except Exception as e: db.session.rollback() # Perform a database rollback '''
 
    try:
        ro2 = Role()
        ro2.name = 'user'
        db.session.add(ro2)
        # After inserting the data, it must be submitted
        db.session.commit()
    except Exception as e:
        db.session.rollback() 
        raise e
 
    try:
        us1 = User(name='wang', email='[email protected]', password='123456', role_id=ro1.id)
        us2 = User(name='zhang', email='[email protected]', password='201512', role_id=ro2.id)
        us3 = User(name='chen', email='[email protected]', password='987654', role_id=ro2.id)
        us4 = User(name='zhou', email='[email protected]', password='456789', role_id=ro1.id)
        us5 = User(name='tang', email='[email protected]', password='158104', role_id=ro2.id)
        us6 = User(name='wu', email='[email protected]', password='5623514', role_id=ro2.id)
        us7 = User(name='qian', email='[email protected]', password='1543567', role_id=ro1.id)
        us8 = User(name='liu', email='[email protected]', password='867322', role_id=ro1.id)
        us9 = User(name='li', email='[email protected]', password='4526342', role_id=ro2.id)
        us10 = User(name='sun', email='[email protected]', password='235523', role_id=ro2.id)
        db.session.add_all([us1, us2, us3, us4, us5, us6, us7, us8, us9, us10])
        db.session.commit()
    except Exception as e:
        db.session.rollback()
        raise e
 
    app.run(debug=True)

4、一对多关系

# 一对多关系：一个HobbyMultiple people can like it,关联字段写在多的一方,Person

class Hobby(Base):
    __tablename__ = 'hobby'
    id = Column(Integer, primary_key=True)
    caption = Column(String(50), default='篮球')


class Person(Base):
    __tablename__ = 'person'
    nid = Column(Integer, primary_key=True)
    name = Column(String(32), index=True, nullable=True)
    # hobby指的是tablename而不是类名,跟hobby表的idFields establish foreign key relationships
    hobby_id = Column(Integer, ForeignKey("hobby.id"))

    # 跟数据库无关,不会新增字段,只用于快速链表操作
    # 类名,backref用于反向查询
    hobby = relationship('Hobby', backref='persons')

5、多对多关系

# 多对多关系：Boy and girl dating,A boy can date multiple girls,A girl can date more than one boy

class Boy2Girl(Base):
    __tablename__ = 'boy2girl'
    id = Column(Integer, primary_key=True, autoincrement=True)
    girl_id = Column(Integer, ForeignKey('girl.id'))
    boy_id = Column(Integer, ForeignKey('boy.id'))


class Girl(Base):
    __tablename__ = 'girl'
    id = Column(Integer, primary_key=True)
    name = Column(String(64), unique=True, nullable=False)


class Boy(Base):
    __tablename__ = 'boy'

    id = Column(Integer, primary_key=True, autoincrement=True) # autoincrement自增
    name = Column(String(64), unique=True, nullable=False)

    # 与生成表结构无关,仅用于查询方便,放在哪个单表中都可以
    girls = relationship('Girl', secondary='boy2girl', backref='boys')

6、SQLAlchemy的增删改

from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker

from models import Users, Person, Hobby, Girl, Boy, Boy2Girl

# Basic addition, deletion, search and modification of a single table

# 第一步：得到engine对象
engine = create_engine("mysql+pymysql://root:[email protected]:3306/aaa", max_overflow=0, pool_size=5)

# 第二步：得到Session对象,as a class
Session = sessionmaker(bind=engine)

# 第三步：创建session对象
# 每次执行数据库操作时,都需要创建一个session
session = Session()

# 第四步：以后使用session来操作数据

# #### 1Add a single
# 先创建出一个user对象
# lqz = Users(name='lqz', email='[email protected]')
# # Add the object to the database
# session.add(lqz) # Only one can be added at a time
# # 提交事务
# session.commit()
# # 把连接放回到池中
# session.close()


##### 2 Add multiple at the same time
# lqz = Users(name='lqz1', email='[email protected]')
# egon = Users(name='egon', email='[email protected]')
#
# lyf=Girl(name='刘亦菲')
# # Add the object to the database
# session.add_all([lqz,egon,lyf])
# # 提交事务
# session.commit()
# # 把连接放回到池中
# session.close()

##### 3 Basic check（Check is the most,Simple now）

# lqz=session.query(Users).filter_by(name='lqz').first() # 查一个,返回Users对象
# lqz=session.query(Users).filter_by(name='lqz').all() # 查所有,返回列表
# print(lqz)


#### 4 删除（Check and delete）
# res=session.query(Users).filter_by(name='lqz').delete()
# session.commit()
# session.close()


### 5 修改
# res=session.query(Users).filter_by(name='lqz1').update({'name':'lqz_nb'})

# 类似于原来的F查询,Take out the fields in the table and use them
# synchronize_session=False Indicates the addition of strings
# res=session.query(Users).filter_by(name='lqz_nb').update({Users.name: Users.name + "099"}, synchronize_session=False)
# synchronize_session="evaluate" Indicates the addition of numbers（If it cannot be converted into data,Actually wrong,直接设为0）
session.query(Users).filter_by(name='1').update({
    "id": Users.id + 10}, synchronize_session="evaluate")
session.commit()
session.close()

7、SQLAlchemy的查

1.The following methods all return a new query,It needs to be used with the actuator.
filter(): 过滤,功能比较强大,多表关联查询.
filter_by()：过滤,It is generally used in filtering scenarios for single-table queries.
order_by()：排序.默认是升序,Descending requires a package import：from sqlalchemy import * .然后引入desc方法.比如order_by(desc("email")).Sort in descending alphabetical order by mailbox.
group_by()：分组.

2.Below are some commonly used actuators：Use with the filter above.
get()：获得idA function equal to a few.
比如：查询id=1的对象.
get(1),切记：Not in parentheses“id=”,直接传入idThe value isok.Because the function of this function is to query the object whose primary key is equal to a few.
all()：查询所有的数据.
first()：查询第一个数据.
count()：返回查询结果的数量.
paginate()：分页查询,Returns a pagination object.
paginate(参数1,参数2,参数3)=>参数1：当前是第几页;参数2：每页显示几条记录;参数3：Whether to return an error.
The returned pagination object has three properties：items：获得查询的结果,pages：Get the total number of pages,page：获得当前页.

3.Commonly used logical symbols：
You need to import the package to use it：from sqlalchemy import * 
not_、and_、or_ And the sort mentioned abovedesc.
Commonly used built-in ones：in_：Indicates what range a field is in.

4.Some database queries for other relationships：
endswith()：以什么结尾.
startswith()：以什么开头.
contains()：包含

示例

1. 查询所有用户数据
User.query.all()
 
2. 查询有多少个用户
User.query.count()
 
3. 查询第1个用户
User.query.first()
 
4. 查询id为4的用户[3种方式]
User.query.get(4)
User.query.filter_by(id=4).first()　　　　
User.query.filter(User.id==4).first()
 
filter:(类名.属性名==)
filter_by:(属性名=)
 
filter_by: 用于查询简单的列名,不支持比较运算符
filter比filter_by的功能更强大,支持比较运算符,支持or_、in_等语法.
 
5. 查询名字结尾字符为g的所有数据[开始/包含]
User.query.filter(User.name.endswith('g')).all()
User.query.filter(User.name.contains('g')).all()
 
6. 查询名字不等于wang的所有数据[2种方式]
from sqlalchemy import not_
PS：The format of the logical query：逻辑符_(Some other judgments of class attributes)
User.query.filter(not_(User.name=='wang')).all()
User.query.filter(User.name!='wang').all()
 
7. 查询名字和邮箱都以 li 开头的所有数据[2种方式]
from sqlalchemy import and_
User.query.filter(and_(User.name.startswith('li'), User.email.startswith('li'))).all()
User.query.filter(User.name.startswith('li'), User.email.startswith('li')).all()
 
8. 查询password是 `123456` 或者 `email` 以 `itheima.com` 结尾的所有数据
from sqlalchemy import or_
User.query.filter(or_(User.password=='123456', User.email.endswith('itheima.com'))).all()
 
9. 查询id为 [1, 3, 5, 7, 9] 的用户列表
User.query.filter(User.id.in_([1, 3, 5, 7, 9])).all()
 
10. 查询name为liu的角色数据：关系引用
User.query.filter_by(name='liu').first().role.name
 
11. 查询所有用户数据,并以邮箱排序
User.query.order_by('email').all()  默认升序
User.query.order_by(desc('email')).all() 降序
 
12. 查询第2页的数据, 每页只显示3条数据
help(User.query.paginate)
pages = User.query.paginate(2, 3, False)
PS：三个参数: 1. The current number of pages to query 2. 每页的数量 3. Whether to return an error
pages.items # 获取查询的结果
pages.pages # 总页数
pages.page # 当前页数

8、Flask-SQLAlchemy使用

# 使用步骤
1 导入from flask_sqlalchemy import SQLAlchemy 实例化得到db对象
2 在app中注册
	db.init_app(app)
3 Table model inheritance db.Model
4  session是db.session
	db.session使用即可
    
    
    
#存在问题
	1 Table migration is troublesome
    2 Dynamic modification of fields is not supported

9、flask-migrate使用

# 像djagno一样,Execute two migration commands,Realize the dynamic migration of the database
# pip install flask-migrate

# 使用步骤
第一步：from flask_migrate import Migrate, MigrateCommand
第二步：执行
Migrate(app, db)
manager.add_command('db', MigrateCommand)

python3 manage.py db init 初始化：只执行一次,生成一个migrations文件夹

# Create a new table directly afterwards,新建字段,执行命令,就会自动同步
python3 manage.py db migrate 等同于 makemigartions
python3 manage.py db upgrade 等同于migrate