Add OneToOne relation type

apart from OneToMany (by ForeignKey) and ManyToMany add also support for OneToOne relations.

[pylakey]

Thanks, I’ll try and make a PR

[bstrdsmkr]

So before I saw your reply, I was looking through the source to see if this was something I could hack in and discovered that the ForeignKey function hardcodes primary_key=False which explains the error above. I monkey patched the field like this:

patched_field = ForeignKey(Files, related_name='contents')
patched_field.primary_key=True

class FileContents(Model):
    class Meta:
        tablename = 'file_contents'
        metadata = sqlalchemy.MetaData(schema='data_reception')
        database=database
    versioned_filename: Files = patched_field
    n_samples: int = Integer()

And that allowed things to continue and me to actually run the query. I’m not sure if this is an “expected” failure (given the impending compound pk work) or a sort of bug that would otherwise allow this kind of work around to work, so thought I’d report it. The query produces SQL like this:

SELECT data_reception.file_info.versioned_filename AS versioned_filename,
	   data_reception.file_info.md5_checksum AS md5_checksum,
	   qb6461_file_contents.versioned_filename AS qb6461_versioned_filename,
	   qb6461_file_contents.n_samples AS qb6461_n_samples
FROM data_reception.file_info
	LEFT OUTER JOIN data_reception.file_contents AS qb6461_file_contents
	ON qb6461_file_contents.versioned_filename=file_info.versioned_filename
WHERE data_reception.file_info.datastream IN ('sgpxsaprvptI6.a1')
AND data_reception.qb6461_file_contents.n_samples >= 500

resulting in an SQL error:

SQL Error [42P01]: ERROR: invalid reference to FROM-clause entry for table "qb6461_file_contents"
  Hint: There is an entry for table "qb6461_file_contents", but it cannot be referenced from this part of the query.

If I remove data_reception (the Postgres Schema) from the AND condition, the query executes as expected.

Is this a new bug with the schema being inappropriately inserted, or a known effect that will be covered by the compound pk work?