Changing constraint naming conventions in Flask-SQLAlchemy

Question

I would like to change the standard naming conventions of constraints that are set in Flask-SQLAlchemy, to ease migrations with Alembic.

As Flask-SQLAlchemy creates the declarative base (where you can supply naming conventions) by itself I'm not sure what the best way is going about doing this. Can I change naming conventions after the declarative base is created (i.e. when I've created the Flask-SQLAlchemy object) or do I have to subclass the SQLAlchemy class? Is there a completely different way?

Answer 1

As of Flask-SQLAlchemy 2.1 you can do the following:

from flask_sqlalchemy import SQLAlchemy
from sqlalchemy import MetaData

metadata = MetaData(
  naming_convention={
    'pk': 'pk_%(table_name)s',
    'fk': 'fk_%(table_name)s_%(column_0_name)s_%(referred_table_name)s',
    'ix': 'ix_%(table_name)s_%(column_0_name)s',
    'uq': 'uq_%(table_name)s_%(column_0_name)s',
    'ck': 'ck_%(table_name)s_%(constraint_name)s',
    }
)
db = SQLAlchemy(metadata=metadata)

Answer 2

Version 2.1 introduced the metadata argument to the extension. If all you want to customize about the base model is the metadata, you can pass a custom MetaData instance to it.

db = SQLAlchemy(metadata=MetaData(naming_convention={
    'pk': 'pk_%(table_name)s',
    'fk': 'fk_%(table_name)s_%(column_0_name)s_%(referred_table_name)s',
    'ix': 'ix_%(table_name)s_%(column_0_name)s',
    'uq': 'uq_%(table_name)s_%(column_0_name)s',
    'ck': 'ck_%(table_name)s_%(constraint_name)s',
}))

---

Previously, you would subclass the SQLAlchemy class and override make_declarative_base. This still works, and is useful if you need to further customize the base model.

from flask_sqlalchemy import SQLAlchemy as BaseSQLAlchemy, Model, _BoundDeclarativeMeta, _QueryProperty
from sqlalchemy import MetaData

class SQLAlchemy(BaseSQLAlchemy):
    def make_declarative_base(self):
        metadata = MetaData(naming_convention={
            'pk': 'pk_%(table_name)s',
            'fk': 'fk_%(table_name)s_%(column_0_name)s_%(referred_table_name)s',
            'ix': 'ix_%(table_name)s_%(column_0_name)s',
            'uq': 'uq_%(table_name)s_%(column_0_name)s',
            'ck': 'ck_%(table_name)s_%(constraint_name)s',
        })
        base = declarative_base(metadata=metadata, cls=Model, name='Model', metaclass=_BoundDeclarativeMeta)
        base.query = _QueryProperty(self)
        return base