在 Flask SQLALchemy 模型中处理业务逻辑的正确方法是什么？

Question

I'm wondering what's the proper way of retrieving data from the model. Let's take the classes below for the example:

class A(db.Model):
   def get_attributes():
       return self.product_category.attributes

class Attribute(db.Mdel):
    attribute_id = db.Column(db.Integer, primary_key=True, autoincrement=True)
    label = db.Column(db.String(255), nullable=False)

Let's say that calling get_attributes() returns three objects of the Attribute class.

In my route , I only want to receive the list of attribute labels. What I'm currently doing is looping through the objects and retrieve the label property like this:

labels = [i.label for i in obj.get_attributes()]

Which I don't think is a proper way of doing it. Is there any better way to achieve this?

Answer 1

You should use relationship between A and Attribute.

For example

class A(db.Model):
    # ...
    # table primary key, columns etc.
    # ...
    attributes = db.relationship(
        "Attribute",
        backref="as",
        lazy=True
    )

class Attribute(db.Model):
    # ...
    # table primary key, columns etc.
    # ...
    a_id = db.Column(db.Integer, db.ForeignKey('a.id'))

After that, you can access certain "a" attributes with a.attributes. To add an attribute to "a" just: a.attributes.append(a)