Add ondelete='CASCADE' to existing foreignkey

[Hồng Quân Nguyễn]

Hi

I defined a model with a column as foreignkey, but forgot to include
"ondelete='CASCADE'". Now I want to add this, how should I do? (alembic
revision --auto doesn't support)

[Michael Bayer]

i believe you need to drop the foreign key and re-create it.

Hi
I defined a model with a column as foreignkey, but forgot to include "ondelete='CASCADE'". Now I want to add this, how should I do? (alembic revision --auto doesn't support)
Thanks.
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[Nguyễn Hồng Quân]

Hi Michael,

Could you please tell me how the function, syntax is.

In the Alembic documentation, I can see create_foreign_key but not
drop_foreign_key. I guess drop_constraint can be used, but please give me
an example.
Another thing is that the foreign_key generated by
Column('owner_id', Integer, ForeignKey('owners.id'))
doesn't have a name, but drop_constraint require the constraint's name to
drop.

Post by Michael Bayer
i believe you need to drop the foreign key and re-create it.
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[Michael Bayer]

Post by Nguyễn Hồng Quân
Hi Michael,
Could you please tell me how the function, syntax is.

it’s drop_constraint:

op.drop_constraint(“name_of_fk”)

Post by Nguyễn Hồng Quân
Another thing is that the foreign_key generated by
Column('owner_id', Integer, ForeignKey('owners.id'))
doesn't have a name, but drop_constraint require the constraint's name to drop.

the database always gives it a name, you can see it with a script like this:

from sqlalchemy import create_engine, inspect

eng = create_engine(“
”)
insp = inspect(eng)

print(insp.get_foreign_keys(“my_table”))