type modifier is not allowed for type "geometry" when updating DB with postgis via geoalchemy2 & alembic

Question

My alembic update script for adding a new postgis geometry point looks like this:

from alembic import op
import sqlalchemy as sa
import geoalchemy2 as ga

def upgrade():
    op.add_column('stuff', sa.Column('my_location', ga.Geometry('POINT', management=True)))


def downgrade():
    pass

When I run the script via

alembic upgrade head

the following error occurs

sqlalchemy.exc.ProgrammingError: (psycopg2.ProgrammingError) type modifier is not allowed for type "geometry"
LINE 1: ALTER TABLE events ADD COLUMN location geometry(POINT,-1)

I am using postgres 9.1, postgis 1.5, sqlalchemy 1.0.9, geoalchemy2 0.2.6.

score 2 · Answer 1 · edited Feb 26 '16 at 15:23

You are using Postgis 1.5, which does not support type modifier for the geometry type.

How to fix the issue: Postgis 1.5 is currently quite old, so upgrade to Postgis 2.x

If for same reason you cannot upgrade your Postgis installation, the correct way to add a geometry column is using the function AddGeometryColumn(). The SQL statement looks so:

SELECT AddGeometryColumn ('public','events','geom',0,'POINT',2);

where the arguments mean:

1) schema name, 2) table name, 3) column name, 4) srid, 5) type, 6) dimension.

However you are already using the correct flag for adding geometry column in Postgis 1.5: management=True. In accordance to to documentation, this should force SqlAlchemy to use the AddGeometryColumn() syntax. Maybe the error is coming from Alembic an not from GeoAlchemy?

type modifier is not allowed for type "geometry" when updating DB with postgis via geoalchemy2 & alembic

1 Answers1