id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
27478	JSONB_AGG is not available in PostgreSQL 9.4	Christian von Roques	nobody	"`django.contrib.postgres.aggregates.general.JsonAgg` uses `JSONB_AGG`. The Django test-suite contains a test which fails due to `JSONB_AGG` being unavailable as shown below when run against PostgreSQL 9.4. The test is already marked as `@skipUnlessDBFeature('has_jsonb_datatype')`, but JSONB became available with PostgreSQL 9.4 and `JSONB_AGG` was added in PostgreSQL 9.5.
I currently see three possibilities:
 1. Add a new feature `has_jsonb_agg` and make the test `@skipUnlessDBFeature('has_jsonb_agg')`
 2. Add a new feature `has_jsonb_agg` and use `JSON_AGG` instead of `JSONB_AGG` when `JSONB_AGG` is unavailable.
3. Have `has_jsonb_datatype` lie about it not being available in PostgreSQL 9.4.
I prefer and have implemented option 2 and really don't like option 3.

See my [https://github.com/roques/django/tree/jsonb_agg branch] for my initial implementation. — Is there a cleaner way to achieve this besides redefining `JsonAgg.as_sql`?

{{{
ERROR: test_json_agg (postgres_tests.test_aggregates.TestGeneralAggregate)
----------------------------------------------------------------------
Traceback (most recent call last):
  File ""/usr/lib/python3.4/unittest/case.py"", line 58, in testPartExecutor
    yield
  File ""/usr/lib/python3.4/unittest/case.py"", line 577, in run
    testMethod()
  File ""/home/roques/tools/django/django/test/testcases.py"", line 1113, in skip_wrapper
    return test_func(*args, **kwargs)
  File ""/home/roques/tools/django/tests/postgres_tests/test_aggregates.py"", line 122, in test_json_agg
    values = AggregateTestModel.objects.aggregate(jsonagg=JsonAgg('char_field'))
  File ""/home/roques/tools/django/django/db/models/manager.py"", line 85, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File ""/home/roques/tools/django/django/db/models/query.py"", line 352, in aggregate
    return query.get_aggregation(self.db, kwargs.keys())
  File ""/home/roques/tools/django/django/db/models/sql/query.py"", line 461, in get_aggregation
    result = compiler.execute_sql(SINGLE)
  File ""/home/roques/tools/django/django/db/models/sql/compiler.py"", line 829, in execute_sql
    cursor.execute(sql, params)
  File ""/home/roques/tools/django/django/db/backends/utils.py"", line 64, in execute
    return self.cursor.execute(sql, params)
  File ""/home/roques/tools/django/django/db/utils.py"", line 94, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File ""/home/roques/tools/django/django/utils/six.py"", line 685, in reraise
    raise value.with_traceback(tb)
  File ""/home/roques/tools/django/django/db/backends/utils.py"", line 64, in execute
    return self.cursor.execute(sql, params)
django.db.utils.ProgrammingError: function jsonb_agg(character varying) does not exist
LINE 1: SELECT JSONB_AGG(""postgres_tests_aggregatetestmodel"".""char_f...
               ^
HINT:  No function matches the given name and argument types. You might need to add explicit type casts.
}}}"	Cleanup/optimization	closed	contrib.postgres	dev	Normal	duplicate	JsonAgg JSONB_AGG	Christian von Roques	Unreviewed	1	0	0	0	0	0