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使用flask-sqlalchemy扩展后,如何把Model类定义文件分散在不同的文件夹?

2017-06-07
kyle

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

http://www.pythondoc.com/flask-sqlalchemy/quickstart.html

https://github.com/svieira/Budget-Manager


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