Cannot use Postgres's ARRAY with SQLAlchemy

Question

I cannot add a 2D integer array to Postgre using this code with SQLAlchemy:

    def create_polygon(x, y, w, h):
        polygon = []
        polygon.append([1, 2])
        return polygon


    engine = create_engine('postgresql://usr:pwd@localhost:5432/db', echo=True)
    meta = MetaData()

    table = Table(
        'table', meta,
        Column('id', Integer, primary_key=True), 
        Column('polygon', ARRAY(Integer, dimensions=2))
    )
    meta.create_all(engine)

    conn = engine.connect()

    for line in lines:            
        insert = zone_by_cam.insert(
            polygon = create_polygon(*line.params)
        )

        conn.execute(insert)

I got this error message:

Additional arguments should be named <dialectname>_<argument>, got 'polygon'

I then changed the name of polygon to postgresql_polygon (which is nowhere to be found in the docs), and have this one instead:

Argument 'postgresql_polygon' is not accepted by dialect 'postgresql' on behalf of <class 'sqlalchemy.sql.dml.Insert'>

How can I fix this? Thanks!

Answer 1

Table.insert() does not accept values to insert as keyword arguments, and passes any keyword arguments it does not handle to the dialect specific implementation of Insert . The error then is telling you that the implementation expects those arguments to follow the format <dialectname>_<argument> , but you gave it polygon . postgresql_polygon is not in the Postgresql dialect documentation , since no such argument exists. The initial fix is simple, pass values as a dict in the keyword argument values , or use Insert.values() :

for line in lines:            
    insert = zone_by_cam.insert().values(
        polygon=create_polygon(*line.params)
    )

    conn.execute(insert)

Instead of separate inserts you could also pass all your "polygons" in a single executemany operation:

insert = zone_by_cam.insert().values([
    {'polygon': create_polygon(*line.params)} for line in lines
])

conn.execute(insert)