Reflecting table containing only oid column raises NoSuchTableError

Migrated issue, originally created by Ulrich Petri (@ulope)

I ran into what I think is a bug while trying to reflect a legacy database that contained a table with no columns except for the Postgres oid column (don’t ask why…). That table had been created with the “WITH OIDS” option.

When using reflection on a table like this a NoSuchTable exception is raised.

The reason for that lies in sqlalchemy.engine.reflection.reflecttable. The found_table flag is set to true inside the column processing loop. This loop is not executed in my case because sqlalchemy.dialects.postgresql.base.PGDialect.get_columns excludes attributes with an attnum < 1 (attnum for the oid column is -2) returning an empty list in this case.

I’m aware that this is a very unusual case. But I’d argue that at least the exception is misleading and should be changed since the table clearly exists.

Minimal example:

createdb test
psql test <<EOF
create table test () with oids;
EOF

from sqlalchemy import create_engine, MetaData
engine = create_engine("postgresql+psycopg2://localhost/test")
meta = MetaData()
meta.reflect(bind=engine)

[zzzeek]

oh yes, that works fine sure. this issue is about reflection

[sqla-tester]

Sumit Khanna has proposed a fix for this issue in the main branch:

Reflect table can reflect table with no columns https://gerrit.sqlalchemy.org/c/sqlalchemy/sqlalchemy/+/3164