alembic create_table, check if table exists

问题

I have an alembic upgrade script that creates a table, however I don't want it to create the table if it already exists.

According to the alembic doc, I can pass in keyword args to op.create_tables that are acceptable to sqlalchemy.schema.table, so I'm using the keep_existing keyword:

op.create_table('foo_model',
  sa.Column('foo_id', sa.Integer(), nullable=False),
  sa.Column('foo_str', sa.String(length=255), nullable=True),
  sa.PrimaryKeyConstraint('foo_id'),
  keep_existing= True
  )

However I'm still getting the table already exists error.

sqlalchemy.exc.InternalError: (InternalError) (1050, u"Table 'foo_model' already exists") '\nCREATE TABLE foo_model (\n\tfoo_id INTEGER NOT NULL AUTO_INCREMENT, \n\tfoo_str VARCHAR(255), \n\tPRIMARY KEY (foo_id)\n)\n\n' ()

回答1:

You can get the list of existing tables like this:

conn = op.get_bind()
inspector = Inspector.from_engine(conn)
tables = inspector.get_table_names()

and then check if table already exists or not

if table_name not in tables:
   op.create_table()

回答2:

As it has been said elsewhere ( Check if a table column exists in the database using SQLAlchemy and Alembic) alembic should reflect the full state of your database, that means it would automatically know if a table exists.

Make sure you define the upgrade and downgrade, so that if upgrade creates the table downgrade removes it.

If you do this you can just "downgrade" to the previous revision and upgrade again and it will work. Use autogenerate on a revision to create the initial state.

回答3:

It's probably because the table already exists. Just drop the table from your database by using psql and running drop table foo_model;

来源：https://stackoverflow.com/questions/31299709/alembic-create-table-check-if-table-exists

标签

python

database-migration

alembic