sub-classing a peewee field type to add behavior

Question

I am trying to add the required behavior to a CharFiled or TextField so I can store a list of lists and retrieve it as a list of lists again. I am not asking for a solution rather I would like to see an example where a subclassing of an already supported field type is done as I didn't find any in the documentation or the Internet.

Do I have to do it as explained in the documents for creating a custom type?

for example:

class mylistoflists(TextField):

if yes, then what do I have to assign to field_type?

Answer 1

Example code (see tests/fields.py for full example):

class ListField(TextField):
    def db_value(self, value):
        return ','.join(value) if value else ''

    def python_value(self, value):
        return value.split(',') if value else []


class Todo(TestModel):
    content = TextField()
    tags = ListField()


class TestCustomField(ModelTestCase):
    requires = [Todo]

    def test_custom_field(self):
        t1 = Todo.create(content='t1', tags=['t1-a', 't1-b'])
        t2 = Todo.create(content='t2', tags=[])

        t1_db = Todo.get(Todo.id == t1.id)
        self.assertEqual(t1_db.tags, ['t1-a', 't1-b'])

        t2_db = Todo.get(Todo.id == t2.id)
        self.assertEqual(t2_db.tags, [])

        t1_db = Todo.get(Todo.tags == Value(['t1-a', 't1-b'], unpack=False))
        self.assertEqual(t1_db.id, t1.id)