Alembic/Flask-Migrate not detecting after_create events - flask

Question

I have a simple Flask-SQLAlchemy model (with event listener to create trigger):
from flask_sqlalchemy import SQLAlchemy
db = SQLAlchemy()
class Confirm(db.Model):
created = db.Column(db.DateTime, default=db.func.current_timestamp(), nullable=False)
modified = db.Column(db.DateTime, default=db.func.current_timestamp(), onupdate=db.func.current_timestamp(), nullable=False)
id = db.Column(db.String(36), primary_key=True)
class ConfirmOld(db.Model):
orig_created = db.Column(db.DateTime)
orig_modified = db.Column(db.DateTime)
orig_id = db.Column(db.String(36))
confirm_delete = DDL('''\
CREATE TRIGGER confirm_delete
BEFORE DELETE
ON confirm FOR EACH ROW
BEGIN
INSERT INTO confirm_old ( orig_created, orig_modified, orig_id )
VALUES ( OLD.created, OLD.modified, OLD.id );
END;
''')
event.listen(Confirm.__table__, 'after_create', confirm_delete)
When I run Alembic migrate and upgrade, the TRIGGER is not created (in MySQL). However, it is created and works properly when I use db.create_all().
Is it possible to get Alembic / Flask-Migrate to create and manage my triggers (i.e., custom DDL that is run on after_create events)?

Answer 1

I have faced the same issue tried a solution with Replacable object but didn't work:
I manage to make it work by editing the migration script and execute the trigger creation query.
Here are the step:
Run flask db migrate -m 'adding custom trigger on table x it will generate a migration script for you under version sub-folder of migration folder.
check the folder created under version and edit it like this :
create your trigger query like this :
in the file :
trigger = '''
CREATE TRIGGER confirm_delete
BEFORE DELETE
ON confirm FOR EACH ROW
BEGIN
INSERT INTO confirm_old ( orig_created, orig_modified, orig_id )
VALUES ( OLD.created, OLD.modified, OLD.id );
END;
'''
in the upgrade method :
add this line :
def upgrade():
# ### commands auto generated by Alembic - please adjust! ###
# ### end Alembic commands ###
### add your queries here execute
op.execute(trigger)
If you run flask db upgrade it will execute the query and update the database
to downgrade the database add this in the downgrade method:
def downgrade():
# ### commands auto generated by Alembic - please adjust! ###
# ### end Alembic commands ###
op.execute('drop trigger if exists confirm_delete on confirm cascade;')
If you check your database change will be applied .
PS : The more elegant solution should be what is suggest here
with Replaceable object , tried it but It doesn't work may be my alembic is not update .
Here is how the solution should looks like:
create a ReplaceableObjects class :
class ReplaceableObject(object):
def __init__(self, name, sqltext):
self.name = name
self.sqltext = sqltext
instantiate it with your query statement.
delete_trigger = ReplaceableObject('delete_trigger', trigger)
Update your upgrade and downgrade function like this :
def upgrade():
op.create_sp(delete_trigger)
def downgrade():
op.drop_sp(delete_trigger)
Hope it will helps others...

Answer 2

in Flask the listen is ignored.
Fixed this by using Table instead.
def after_create_table_handler(table: Table, conn: Connection, **kwargs):
pass
event.listen(Table, 'after_create', after_create_table_handler)