Dealing with Arrays in Flask-SqlAlchemy and MySQL

Question

I have a datamodel where I store a list of values separated by comma (1,2,3,4,5...).

In my code, in order to work with arrays instead of string , I have defined the model like this one:

class MyModel(db.Model):
    pk = db.Column(db.Integer, primary_key=True)
    __fake_array = db.Column(db.String(500), name="fake_array")

    @property
    def fake_array(self):
        if not self.__fake_array:
            return

        return self.__fake_array.split(',')

    @fake_array.setter
    def fake_array(self, value):
        if value:
           self.__fake_array = ",".join(value)
        else:
           self.__fake_array = None

This works perfect and from the point of view of my source code "fake_array" is an array, It's only transformed into string when it's stored in database.

The problem appears when I try to filter by that field. Expressions like this doesn't work:

MyModel.query.filter_by(fake_array="1").all()

It seems that I cant filter using the SqlAlchemy query model .

What can I do here? Is there any way to filter this kind of fields? Is there is a better pattern for the "fake_array" problem?

Thanks!

Answer 1

What you're trying to do should really be replaced with a pair of tables and a relationship between them.

The first table (which I'll call A) contains everything BUT the array column, and it should have a primary key of some sort. You should have another table (which I'll call B) that contains a primary key, a foreign key column to A (which I'll call a_id, and an integer field.

Using this layout, each row in the A table has its associated array in table B where B's a_id == A.id via a join. You can add or remove values from the array by manipulating the rows in table B. You can filter by using a join.

If the order of the values is needed, then create an order column in table B.