Automatically add default value when using flask db migrate with default column instead of server_default

[lulunac27a]

When I run flask db migrate with a column with nullable field and a default value from num = db.Column(db.Float, default=0, nullable=False) with default keyboard parameter from Flask-SQLAlchemy, it returns sa.Column('num', sa.Float(), nullable=False), instead of sa.Column('num', sa.Float(), nullable=False, server_default='0').

[CaselIT]

Hii,

That's working as expected. Use server_default in the definition if you want that to be rendered by alembic

[lulunac27a]

How can I do this?

[CaselIT]

I don't understand what is the question. You want to render sa.Column('num', sa.Float(), nullable=False, server_default='0') so use that instead of db.Column(db.Float, default=0, nullable=False)

[lulunac27a]

What about setting default value of date type to date.today() in default column, what's the equivalent for server_default column?

[CaselIT]

note that setting default=date.today() is wrong, since it will execute the function only once when importing the module.

For the server default you would need to use the function in your db that returns the date, for example CURRENT_DATE in postgresql

[Denilson-Semedo]

To enforce a database-level default, explicitly use server_default in your model:

num = db.Column(db.Float, server_default='0', nullable=False)

This will generate the expected sa.Column('num', sa.Float(), nullable=False, server_default='0') in your Alembic migration.