SQLAlchemy create_all（）不创建表

Question

我正在尝试集成PostgreSQL和SQLAlchemy，但是SQLAlchemy.create_all（）并未从我的模型中创建任何表。

我的代码：

from flask import Flask
from flask.ext.sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'postgresql+psycopg2://login:pass@localhost/flask_app'
db = SQLAlchemy(app)
db.create_all()
db.session.commit()

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

admin = User('admin', '[e-mail]')
guest = User('guest', '[e-mail]')
db.session.add(admin)
db.session.add(guest)
db.session.commit()
users = User.query.all()
print users

但是我得到这个错误： sqlalchemy.exc.ProgrammingError: (ProgrammingError) relation "user" does not exist

我怎样才能解决这个问题？

Answer 1

您应该在create_all()调用之前放置模型类，如下所示：

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)

app.config['SQLALCHEMY_DATABASE_URI'] = 'postgresql+psycopg2://login:pass@localhost/flask_app'
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()
db.session.commit()

admin = User('admin', '[e-mail]')
guest = User('guest', '[e-mail]')
db.session.add(admin)
db.session.add(guest)
db.session.commit()
users = User.query.all()
print users

如果您的模型是在单独的模块中声明的，请在调用之前将其导入create_all()。

说，User模型在名为的文件中models.py，

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)

app.config['SQLALCHEMY_DATABASE_URI'] = 'postgresql+psycopg2://login:pass@localhost/flask_app'
db = SQLAlchemy(app)

# See important note below
from models import User

db.create_all()
db.session.commit()

admin = User('admin', '[e-mail]')
guest = User('guest', '[e-mail]')
db.session.add(admin)
db.session.add(guest)
db.session.commit()
users = User.query.all()
print users

重要说明： 在初始化db对象之后导入模型很重要，因为在models.py_中，您还需要db从此模块导入对象。