diff options
Diffstat (limited to 'lib/sqlalchemy/sql')
| -rw-r--r-- | lib/sqlalchemy/sql/sqltypes.py | 50 | ||||
| -rw-r--r-- | lib/sqlalchemy/sql/type_api.py | 3 |
2 files changed, 52 insertions, 1 deletions
diff --git a/lib/sqlalchemy/sql/sqltypes.py b/lib/sqlalchemy/sql/sqltypes.py index ef1624fa0..215c09e60 100644 --- a/lib/sqlalchemy/sql/sqltypes.py +++ b/lib/sqlalchemy/sql/sqltypes.py @@ -1728,7 +1728,55 @@ class JSON(Indexable, TypeEngine): Index operations return an expression object whose type defaults to :class:`.JSON` by default, so that further JSON-oriented instructions - may be called upon the result type. + may be called upon the result type. Note that there are backend-specific + idiosyncracies here, including that the Postgresql database does not generally + compare a "json" to a "json" structure without type casts. These idiosyncracies + can be accommodated in a backend-neutral way by by making explicit use + of the :func:`.cast` and :func:`.type_coerce` constructs. + Comparison of specific index elements of a :class:`.JSON` object + to other objects work best if the **left hand side is CAST to a string** + and the **right hand side is rendered as a json string**; a future SQLAlchemy + feature such as a generic "astext" modifier may simplify this at some point: + + * **Compare an element of a JSON structure to a string**:: + + from sqlalchemy import cast, type_coerce + from sqlalchemy import String, JSON + + cast( + data_table.c.data['some_key'], String + ) == '"some_value"' + + cast( + data_table.c.data['some_key'], String + ) == type_coerce("some_value", JSON) + + * **Compare an element of a JSON structure to an integer**:: + + from sqlalchemy import cast, type_coerce + from sqlalchemy import String, JSON + + cast(data_table.c.data['some_key'], String) == '55' + + cast( + data_table.c.data['some_key'], String + ) == type_coerce(55, JSON) + + * **Compare an element of a JSON structure to some other JSON structure** - note + that Python dictionaries are typically not ordered so care should be taken + here to assert that the JSON structures are identical:: + + from sqlalchemy import cast, type_coerce + from sqlalchemy import String, JSON + import json + + cast( + data_table.c.data['some_key'], String + ) == json.dumps({"foo": "bar"}) + + cast( + data_table.c.data['some_key'], String + ) == type_coerce({"foo": "bar"}, JSON) The :class:`.JSON` type, when used with the SQLAlchemy ORM, does not detect in-place mutations to the structure. In order to detect these, the diff --git a/lib/sqlalchemy/sql/type_api.py b/lib/sqlalchemy/sql/type_api.py index 98ede4e66..bb9de20fc 100644 --- a/lib/sqlalchemy/sql/type_api.py +++ b/lib/sqlalchemy/sql/type_api.py @@ -1213,6 +1213,9 @@ class Variant(TypeDecorator): self.impl = base self.mapping = mapping + def coerce_compared_value(self, operator, value): + return self.impl.coerce_compared_value(operator, value) + def load_dialect_impl(self, dialect): if dialect.name in self.mapping: return self.mapping[dialect.name] |