flask-sqlalchemy

一旦创建，这个对象就包含 sqlalchemy 和 sqlalchemy.orm 中的所有函数和助手。此外它还提供一个名为 Model 的类，用于作为声明模型时的 delarative 基类:

<span style="color: #0000ff">from</span> flask <span style="color: #0000ff">import</span><span style="color: #000000"> Flask
</span><span style="color: #0000ff">from</span> flask.ext.sqlalchemy <span style="color: #0000ff">import</span><span style="color: #000000"> SQLAlchemy
app </span>= Flask(<span style="color: #800080">__name__</span><span style="color: #000000">)
app.config[</span><span style="color: #800000">‘</span><span style="color: #800000">SQLALCHEMY_DATABASE_URI</span><span style="color: #800000">‘</span>] = <span style="color: #800000">‘</span><span style="color: #800000">sqlite:////tmp/test.db</span><span style="color: #800000">‘</span><span style="color: #000000">
db </span>=<span style="color: #000000"> SQLAlchemy(app)
</span><span style="color: #0000ff">class</span><span style="color: #000000"> User(db.Model):
    id </span>= db.Column(db.Integer, primary_key=<span style="color: #000000">True)
    username </span>= db.Column(db.String(80), unique=<span style="color: #000000">True)
    email </span>= db.Column(db.String(120), unique=<span style="color: #000000">True)
    </span><span style="color: #0000ff">def</span> <span style="color: #800080">__init__</span><span style="color: #000000">(self, username, email):
        self.username </span>=<span style="color: #000000"> username
        self.email </span>=<span style="color: #000000"> email
    </span><span style="color: #0000ff">def</span> <span style="color: #800080">__repr__</span><span style="color: #000000">(self):
        </span><span style="color: #0000ff">return</span> <span style="color: #800000">‘</span><span style="color: #800000"><User %r></span><span style="color: #800000">‘</span> % self.username

为了创建初始数据库，只需要从交互式 Python shell 中导入 db 对象并且调用 SQLAlchemy.create_all() 方法来创建表和数据库:

>>> <span style="color: #0000ff">from</span> yourapplication <span style="color: #0000ff">import</span><span style="color: #000000"> db
</span>>>> db.create_all()

Boom, 您的数据库已经生成。现在来创建一些用户:

>>> <span style="color: #0000ff">from</span> yourapplication <span style="color: #0000ff">import</span><span style="color: #000000"> User
</span>>>> admin = User(<span style="color: #800000">‘</span><span style="color: #800000">admin</span><span style="color: #800000">‘</span>, <span style="color: #800000">‘</span><span style="color: #800000">admin@example.com</span><span style="color: #800000">‘</span><span style="color: #000000">)
</span>>>> guest = User(<span style="color: #800000">‘</span><span style="color: #800000">guest</span><span style="color: #800000">‘</span>, <span style="color: #800000">‘</span><span style="color: #800000">guest@example.com</span><span style="color: #800000">‘</span>)

但是它们还没有真正地写入到数据库中，因此让我们来确保它们已经写入到数据库中:

>>><span style="color: #000000"> db.session.add(admin)
</span>>>><span style="color: #000000"> db.session.add(guest)
</span>>>> db.session.commit()

访问数据库中的数据也是十分简单的:

>>> users =<span style="color: #000000"> User.query.all()
[</span><User u<span style="color: #800000">‘</span><span style="color: #800000">admin</span><span style="color: #800000">‘</span>>, <User u<span style="color: #800000">‘</span><span style="color: #800000">guest</span><span style="color: #800000">‘</span>><span style="color: #000000">]
</span>>>> admin = User.query.filter_by(username=<span style="color: #800000">‘</span><span style="color: #800000">admin</span><span style="color: #800000">‘</span><span style="color: #000000">).first()
</span><User u<span style="color: #800000">‘</span><span style="color: #800000">admin</span><span style="color: #800000">‘</span>>

简单的关系

SQLAlchemy 连接到关系型数据库，关系型数据最擅长的东西就是关系。因此，我们将创建一个使用两张相互关联的表的应用作为例子:

<span style="color: #0000ff">from</span> datetime <span style="color: #0000ff">import</span><span style="color: #000000"> datetime
</span><span style="color: #0000ff">class</span><span style="color: #000000"> Post(db.Model):
    id </span>= db.Column(db.Integer, primary_key=<span style="color: #000000">True)
    title </span>= db.Column(db.String(80<span style="color: #000000">))
    body </span>=<span style="color: #000000"> db.Column(db.Text)
    pub_date </span>=<span style="color: #000000"> db.Column(db.DateTime)
    category_id </span>= db.Column(db.Integer, db.ForeignKey(<span style="color: #800000">‘</span><span style="color: #800000">category.id</span><span style="color: #800000">‘</span><span style="color: #000000">))
    category </span>= db.relationship(<span style="color: #800000">‘</span><span style="color: #800000">Category</span><span style="color: #800000">‘</span><span style="color: #000000">,
        backref</span>=db.backref(<span style="color: #800000">‘</span><span style="color: #800000">posts</span><span style="color: #800000">‘</span>, lazy=<span style="color: #800000">‘</span><span style="color: #800000">dynamic</span><span style="color: #800000">‘</span><span style="color: #000000">))
    </span><span style="color: #0000ff">def</span> <span style="color: #800080">__init__</span>(self, title, body, category, pub_date=<span style="color: #000000">None):
        self.title </span>=<span style="color: #000000"> title
        self.body </span>=<span style="color: #000000"> body
        </span><span style="color: #0000ff">if</span> pub_date <span style="color: #0000ff">is</span><span style="color: #000000"> None:
            pub_date </span>=<span style="color: #000000"> datetime.utcnow()
        self.pub_date </span>=<span style="color: #000000"> pub_date
        self.category </span>=<span style="color: #000000"> category
    </span><span style="color: #0000ff">def</span> <span style="color: #800080">__repr__</span><span style="color: #000000">(self):
        </span><span style="color: #0000ff">return</span> <span style="color: #800000">‘</span><span style="color: #800000"><Post %r></span><span style="color: #800000">‘</span> %<span style="color: #000000"> self.title
</span><span style="color: #0000ff">class</span><span style="color: #000000"> Category(db.Model):
    id </span>= db.Column(db.Integer, primary_key=<span style="color: #000000">True)
    name </span>= db.Column(db.String(50<span style="color: #000000">))
    </span><span style="color: #0000ff">def</span> <span style="color: #800080">__init__</span><span style="color: #000000">(self, name):
        self.name </span>=<span style="color: #000000"> name
    </span><span style="color: #0000ff">def</span> <span style="color: #800080">__repr__</span><span style="color: #000000">(self):
        </span><span style="color: #0000ff">return</span> <span style="color: #800000">‘</span><span style="color: #800000"><Category %r></span><span style="color: #800000">‘</span> % self.name

首先让我们创建一些对象:

>>> py = Category(<span style="color: #800000">‘</span><span style="color: #800000">Python</span><span style="color: #800000">‘</span><span style="color: #000000">)
</span>>>> p = Post(<span style="color: #800000">‘</span><span style="color: #800000">Hello Python!</span><span style="color: #800000">‘</span>, <span style="color: #800000">‘</span><span style="color: #800000">Python is pretty cool</span><span style="color: #800000">‘</span><span style="color: #000000">, py)
</span>>>><span style="color: #000000"> db.session.add(py)
</span>>>> db.session.add(p)

现在因为我们在 backref 中声明了 posts 作为动态关系，查询显示为:

>>><span style="color: #000000"> py.posts
</span><sqlalchemy.orm.dynamic.AppenderBaseQuery object at 0x1027d37d0>

它的行为像一个普通的查询对象，因此我们可以查询与我们测试的 “Python” 分类相关的所有文章(posts):

>>><span style="color: #000000"> py.posts.all()
[</span><Post <span style="color: #800000">‘</span><span style="color: #800000">Hello Python!</span><span style="color: #800000">‘</span>>]

flask-sqlalchemy

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