sqlalchemy.exc.ProgrammingError: (psycopg2.ProgrammingError) can't adapt type 'property'

Question

I'm attempting to query Version where I wish to get objects back where their max_version_number attribute equals the version_number:

latest_versions = \
    dbSession.query(Version).filter(Version.max_version_number == Version.number_version)

This results in an error:

Traceback (most recent call last):
...
...
    filter(Version.max_version_number == Version.version_number).\
  File "c:\python27\lib\site-packages\sqlalchemy\orm\query.py", line 2588, in all
    return list(self)
  File "c:\python27\lib\site-packages\sqlalchemy\orm\query.py", line 2736, in __iter__
    return self._execute_and_instances(context)
  File "c:\python27\lib\site-packages\sqlalchemy\orm\query.py", line 2751, in _execute_and_instances
    result = conn.execute(querycontext.statement, self._params)
  File "c:\python27\lib\site-packages\sqlalchemy\engine\base.py", line 914, in execute
    return meth(self, multiparams, params)
  File "c:\python27\lib\site-packages\sqlalchemy\sql\elements.py", line 323, in _execute_on_connection
    return connection._execute_clauseelement(self, multiparams, params)
  File "c:\python27\lib\site-packages\sqlalchemy\engine\base.py", line 1010, in _execute_clauseelement
    compiled_sql, distilled_params
  File "c:\python27\lib\site-packages\sqlalchemy\engine\base.py", line 1146, in _execute_context
    context)
  File "c:\python27\lib\site-packages\sqlalchemy\engine\base.py", line 1341, in _handle_dbapi_exception
    exc_info
  File "c:\python27\lib\site-packages\sqlalchemy\util\compat.py", line 200, in raise_from_cause
    reraise(type(exception), exception, tb=exc_tb, cause=cause)
  File "c:\python27\lib\site-packages\sqlalchemy\engine\base.py", line 1139, in _execute_context
    context)
  File "c:\python27\lib\site-packages\sqlalchemy\engine\default.py", line 450, in do_execute
    cursor.execute(statement, parameters)
sqlalchemy.exc.ProgrammingError: (psycopg2.ProgrammingError) can't adapt type 'property' [SQL: 'SELECT "Versions".id AS "Versions_id", "Links".id AS "Links_id", "Entities".id AS "Entities_id", "SimpleEntities".stalker_version AS "SimpleEntities_stalker_version", "SimpleEntities".id AS "SimpleEntities_id", "SimpleEntities".entity_type AS "SimpleEntities_entity_type", "SimpleEntities".name AS "SimpleEntities_name", "SimpleEntities".description AS "SimpleEntities_description", "SimpleEntities".created_by_id AS "SimpleEntities_created_by_id", "SimpleEntities".updated_by_id AS "SimpleEntities_updated_by_id", "SimpleEntities".date_created AS "SimpleEntities_date_created", "SimpleEntities".date_updated AS "SimpleEntities_date_updated", "SimpleEntities".type_id AS "SimpleEntities_type_id", "SimpleEntities".generic_text AS "SimpleEntities_generic_text", "SimpleEntities".thumbnail_id AS "SimpleEntities_thumbnail_id", "SimpleEntities".html_style AS "SimpleEntities_html_style", "SimpleEntities".html_class AS "SimpleEntities_html_class", "Links".original_filename AS "Links_original_filename", "Links".full_path AS "Links_full_path", "Versions".task_id AS "Versions_task_id", "Versions".take_name AS "Versions_take_name", "Versions".version_number AS "Versions_version_number", "Versions".is_published AS "Versions_is_published", "Versions".created_with AS "Versions_created_with", "Versions".parent_id AS "Versions_parent_id" \nFROM "SimpleEntities" JOIN "Entities" ON "SimpleEntities".id = "Entities".id JOIN "Links" ON "Entities".id = "Links".id JOIN "Versions" ON "Links".id = "Versions".id \nWHERE "Versions".version_number = %(version_number_1)s'] [parameters: {'version_number_1': <property object at 0x00000000060EF6D8>}]

What am I doing wrong?

Here's the Version model.

This is my actual query which works without issues:

proj_id = 5
versions = Version.query.join(Task).filter(Task.project_id == proj_id).all()

...however, that returns all versions and I wish to get only the ones of the highest version number returned from the query, which is why I'm attempting to filter on that as well.

Answer 1

The problem is that you're passing a property descriptor object (Version.max_version_number) to compare, which psycopg2 has no idea about how to adapt. Instead you should use an SQL expression one way or the other. A common approach is to use hybrid attributes.

To get the rows with maximum versions grouped by tasks in project project_id you can use DISTINCT ON combined with ORDER BY in Postgresql:

versions = Version.query\
    .join(Task)\
    .distinct(Version.task_id)\
    .filter(Task.project_id == proj_id)\
    .order_by(Version.task_id, Version.version_number.desc())\
    .all()

This will return just 1 Version per Task though, even if multiple instances of Version shared the same Version.version_number, which on the other hand would seem strange.

Another option is to use a subquery as a lookup of sorts and join to that:

from sqlalchemy import tuple_

max_per_task = dbSession.query(Version.task_id,
                               func.max(Version.version_number).label('max'))\
    .join(Task)\
    .filter(Task.project_id == proj_id)\
    .group_by(Version.task_id)\
    .subquery()

versions = Version.query\
    .join(max_per_task,
          tuple_(max_per_task.c.task_id, max_per_task.c.max) ==
          tuple_(Version.task_id, Version.version_number))\
    .all()

Answer 2

In my case, I added a non-string variable inside the insert statement was

sys_message = sys.exc_info() # none string value
new_error = error_board(sys_message=sys_message)

will return this error

sqlalchemy.exc.ProgrammingError: (psycopg2.ProgrammingError) can't adapt type 'type'

to solve it make sure you submit a valid data type

It should be

str(sys.exc_info ()) # string value
new_error = error_board(sys_message=sys_message)