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
28214	IndexError for JSONField queries containing percent character in key.	mrsanders	André Ericson	"Using Django 1.11.1 and Postgres 9.5.6.

A JSON field may legitimately contain a percent symbol in a key, for example:

{{{#!javascript
{""%total"": 10}
}}}

This may be queried as follows (assuming the JSONField in the Django model is called 'my_json_field'):

{{{
>>> qs=MyModel.objects.filter(**{""my_json_field__%total"": 10})
}}}

However when the Queryset is evaluated, it raises an IndexError:

{{{
>>> len(qs)
Traceback (most recent call last):
  File ""<console>"", line 1, in <module>
  File ""/usr/local/lib/python3.6/site-packages/django/db/models/query.py"", line 232, in __len__
    self._fetch_all()
  File ""/usr/local/lib/python3.6/site-packages/django/db/models/query.py"", line 1103, in _fetch_all
    self._result_cache = list(self._iterable_class(self))
  File ""/usr/local/lib/python3.6/site-packages/django/db/models/query.py"", line 53, in __iter__
    results = compiler.execute_sql(chunked_fetch=self.chunked_fetch)
  File ""/usr/local/lib/python3.6/site-packages/django/db/models/sql/compiler.py"", line 886, in execute_sql
    raise original_exception
  File ""/usr/local/lib/python3.6/site-packages/django/db/models/sql/compiler.py"", line 876, in execute_sql
    cursor.execute(sql, params)
  File ""/usr/local/lib/python3.6/site-packages/django/db/backends/utils.py"", line 80, in execute
    return super(CursorDebugWrapper, self).execute(sql, params)
  File ""/usr/local/lib/python3.6/site-packages/django/db/backends/utils.py"", line 65, in execute
    return self.cursor.execute(sql, params)
IndexError: tuple index out of range
}}}

...and when attempting to print the generated query, a ValueError is raised:

{{{
>>> print(qs.query)
Traceback (most recent call last):
  File ""<console>"", line 1, in <module>
  File ""/usr/local/lib/python3.6/site-packages/django/db/models/sql/query.py"", line 234, in __str__
    return sql % params
ValueError: unsupported format character 't' (0x74) at index 1498
>>>
}}}

It seems that something isn't escaping the percent before doing a string formatting operation.

Changing the query to double-up the percent symbol causes the query to work (although it shouldn't):
{{{
>>> qs=MyModel.objects.filter(**{""my_json_field__%%total"": 10}
}}}"	Bug	closed	contrib.postgres	1.11	Normal	fixed			Accepted	0	0	0	0	0	0