diff options
Diffstat (limited to 'lib/sqlalchemy')
| -rw-r--r-- | lib/sqlalchemy/orm/query.py | 17 |
1 files changed, 11 insertions, 6 deletions
diff --git a/lib/sqlalchemy/orm/query.py b/lib/sqlalchemy/orm/query.py index 51165287f..39e3db43c 100644 --- a/lib/sqlalchemy/orm/query.py +++ b/lib/sqlalchemy/orm/query.py @@ -236,14 +236,14 @@ class Query(object): return None return self._entities[0].mapper - def _only_mapper_zero(self): + def _only_mapper_zero(self, rationale=None): if len(self._entities) > 1: - raise sa_exc.InvalidRequestError("This operation requires a Query against a single mapper.") + raise sa_exc.InvalidRequestError(rationale or "This operation requires a Query against a single mapper.") return self._mapper_zero() - def _only_entity_zero(self): + def _only_entity_zero(self, rationale=None): if len(self._entities) > 1: - raise sa_exc.InvalidRequestError("This operation requires a Query against a single mapper.") + raise sa_exc.InvalidRequestError(rationale or "This operation requires a Query against a single mapper.") return self._entity_zero() def _generate_mapper_zero(self): @@ -410,7 +410,7 @@ class Query(object): if hasattr(ident, '__composite_values__'): ident = ident.__composite_values__() - key = self._only_mapper_zero().identity_key_from_primary_key(ident) + key = self._only_mapper_zero("get() can only be used against a single mapped class.").identity_key_from_primary_key(ident) return self._get(key, ident) @classmethod @@ -1248,7 +1248,12 @@ class Query(object): def count(self): """Apply this query's criterion to a SELECT COUNT statement.""" - return self._col_aggregate(sql.literal_column('1'), sql.func.count, nested_cols=list(self._only_mapper_zero().primary_key)) + return self._col_aggregate(sql.literal_column('1'), sql.func.count, + nested_cols=list(self._only_mapper_zero( + "Can't issue count() for multiple types of objects or columns. " + " Construct the Query against a single element as the thing to be counted, " + "or for an actual row count use Query(func.count(somecolumn)) or " + "query.values(func.count(somecolumn)) instead.").primary_key)) def _col_aggregate(self, col, func, nested_cols=None): context = QueryContext(self) |