[Sqlalchemy-tickets] Issue #3247: Reflecting table containing only oid column raises NoSuchTableError (zzzeek/sqlalchemy)

[Ulrich P. <iss...@bi...>]

New issue 3247: Reflecting table containing only oid column raises NoSuchTableError
https://bitbucket.org/zzzeek/sqlalchemy/issue/3247/reflecting-table-containing-only-oid

Ulrich Petri:

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:

```
#!bash
createdb test
psql test <<EOF
create table test () with oids;
EOF

```


```
#!python

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