先看官方给的例子
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
DATABASE_USERNAME = 'root'
DATABASE_PASSWORD = '***'
DATABASE_HOST = 'localhost'
DATABASE = 'testdb'
app = Flask(__name__)
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql+mysqldb://%s:%s@%s:3306/%s' % \
(DATABASE_USERNAME, DATABASE_PASSWORD, DATABASE_HOST, DATABASE)
db = SQLAlchemy(app)
class User(db.Model):
id = db.Column(db.Integer, primary_key=True)
username = db.Column(db.String(80), unique=True)
email = db.Column(db.String(120), unique=True)
def __init__(self, username, email):
self.username = username
self.email = email
def __repr__(self):
return '<User %r>' % self.username
db.create_all()
dog = User("Mr.Dog", "liyanhong@baidu.com")
db.session.add(dog)
db.session.commit()
但是假如我们想把User类定义在其他文件中要怎么做呢？ User类构造需要db对象，很自然我们可能会这样写： main.py
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from model import User
DATABASE_USERNAME = 'root'
DATABASE_PASSWORD = '***'
DATABASE_HOST = 'localhost'
DATABASE = 'testdb'
app = Flask(__name__)
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql+mysqldb://%s:%s@%s:3306/%s' % \
(DATABASE_USERNAME, DATABASE_PASSWORD, DATABASE_HOST, DATABASE)
db = SQLAlchemy(app)
db.create_all()
dog = User("Mr.Dog", "liyanhong@baidu.com")
db.session.add(dog)
db.session.commit()
model.py
from main import db
class User(db.Model):
id = db.Column(db.Integer, primary_key=True)
username = db.Column(db.String(80), unique=True)
email = db.Column(db.String(120), unique=True)
def __init__(self, username, email):
self.username = username
self.email = email
def __repr__(self):
return '<User %r>' % self.username
Run起来发现会报错：
ImportError: cannot import name User
为什么呢？ 很简单，这样写会造成循环import。 查了一些资料找到了解决方案： main.py model.py basemodel.py 在同一个目录下
main.py
from flask import Flask
from basemodel import db
from model import User
DATABASE_USERNAME = 'root'
DATABASE_PASSWORD = '***'
DATABASE_HOST = 'localhost'
DATABASE = 'testdb'
app = Flask(__name__)
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql+mysqldb://%s:%s@%s:3306/%s' % \
(DATABASE_USERNAME, DATABASE_PASSWORD, DATABASE_HOST, DATABASE)
db.app = app
db.init_app(app)
db.create_all()
dog = User("Mr.Dog", "liyanhong@baidu.com")
db.session.add(dog)
db.session.commit()
model.py
from basemodel import db
class User(db.Model):
id = db.Column(db.Integer, primary_key=True)
username = db.Column(db.String(80), unique=True)
email = db.Column(db.String(120), unique=True)
def __init__(self, username, email):
self.username = username
self.email = email
def __repr__(self):
return '<User %r>' % self.username
basemodel.py
from flask_sqlalchemy import SQLAlchemy
db = SQLAlchemy()
怎样从已知数据库导出SQLAlchemy Class呢？
pip install sqlacodegen
sqlacodegen mysql://"root":"***"@localhost:3306/testdb --outfile tables.py
参考资料：
https://stackoverflow.com/questions/9692962/flask-sqlalchemy-import-context-issue