Add update_schema_scalar to update a single scalar with name

+ raises TypeError and KeyError instead of GraphQLErrors

Author: leszekhanusz

docs/usage/custom_scalars_and_enums.rst

@@ -92,19 +92,22 @@ where the serialize and parse_value methods simply return the serialized value w
 
 In that case, if you want gql to parse custom scalars to a more useful Python representation,
 or to serialize custom scalars variables from a Python representation,
-then you can use the :func:`update_schema_scalars <gql.utilities.update_schema_scalars>` method
-to modify the definition of the scalars in your schema so that gql could do the parsing/serialization.
+then you can use the :func:`update_schema_scalars <gql.utilities.update_schema_scalars>`
+or :func:`update_schema_scalar <gql.utilities.update_schema_scalar>` methods
+to modify the definition of a scalar in your schema so that gql could do the parsing/serialization.
 
 .. code-block:: python
 
-    from gql.utilities import update_schema_scalars
+    from gql.utilities import update_schema_scalar
 
     with open('path/to/schema.graphql') as f:
         schema_str = f.read()
 
     client = Client(schema=schema_str, ...)
 
-    update_schema_scalars(client.schema, [DatetimeScalar])
+    update_schema_scalar(client.schema, "Datetime", DatetimeScalar)
+
+    # or update_schema_scalars(client.schema, [DatetimeScalar])
 
 .. _enums:
 

gql/utilities/__init__.py

@@ -1,9 +1,10 @@
 from .parse_result import parse_result
 from .update_schema_enum import update_schema_enum
-from .update_schema_scalars import update_schema_scalars
+from .update_schema_scalars import update_schema_scalar, update_schema_scalars
 
 __all__ = [
     "update_schema_scalars",
+    "update_schema_scalar",
     "update_schema_enum",
     "parse_result",
 ]

gql/utilities/update_schema_enum.py

@@ -25,9 +25,9 @@ class Color(Enum):
 
     :param schema: a GraphQL Schema already containing the GraphQLEnumType type.
     :param name: the name of the enum in the GraphQL schema
-    :values: Either a Python Enum or a dict of values. The keys of the provided
+    :param values: Either a Python Enum or a dict of values. The keys of the provided
         values should correspond to the keys of the existing enum in the schema.
-    :use_enum_values: By default, we configure the GraphQLEnumType to serialize
+    :param use_enum_values: By default, we configure the GraphQLEnumType to serialize
         to enum instances (ie: .parse_value() returns Color.RED).
         If use_enum_values is set to True, then .parse_value() returns 0.
         use_enum_values=True is the defaut behaviour when passing an Enum

gql/utilities/update_schema_scalars.py

@@ -1,6 +1,35 @@
 from typing import Iterable, List
 
-from graphql import GraphQLError, GraphQLScalarType, GraphQLSchema
+from graphql import GraphQLScalarType, GraphQLSchema
+
+
+def update_schema_scalar(schema: GraphQLSchema, name: str, scalar: GraphQLScalarType):
+    """Update the scalar in a schema with the scalar provided.
+
+    This can be used to update the default Custom Scalar implementation
+    when the schema has been provided from a text file or from introspection.
+    """
+
+    if not isinstance(scalar, GraphQLScalarType):
+        raise TypeError("Scalars should be instances of GraphQLScalarType.")
+
+    schema_scalar = schema.get_type(name)
+
+    if schema_scalar is None:
+        raise KeyError(f"Scalar '{name}' not found in schema.")
+
+    if not isinstance(schema_scalar, GraphQLScalarType):
+        raise TypeError(
+            f'The type "{name}" is not a GraphQLScalarType,'
+            f"it is a {type(schema_scalar)}"
+        )
+
+    # Update the conversion methods
+    # Using setattr because mypy has a false positive
+    # https://github.com/python/mypy/issues/2427
+    setattr(schema_scalar, "serialize", scalar.serialize)
+    setattr(schema_scalar, "parse_value", scalar.parse_value)
+    setattr(schema_scalar, "parse_literal", scalar.parse_literal)
 
 
 def update_schema_scalars(schema: GraphQLSchema, scalars: List[GraphQLScalarType]):
@@ -11,22 +40,10 @@ def update_schema_scalars(schema: GraphQLSchema, scalars: List[GraphQLScalarType
     """
 
     if not isinstance(scalars, Iterable):
-        raise GraphQLError("Scalars argument should be a list of scalars.")
+        raise TypeError("Scalars argument should be a list of scalars.")
 
     for scalar in scalars:
         if not isinstance(scalar, GraphQLScalarType):
-            raise GraphQLError("Scalars should be instances of GraphQLScalarType.")
-
-        try:
-            schema_scalar = schema.type_map[scalar.name]
-        except KeyError:
-            raise GraphQLError(f"Scalar '{scalar.name}' not found in schema.")
-
-        assert isinstance(schema_scalar, GraphQLScalarType)
+            raise TypeError("Scalars should be instances of GraphQLScalarType.")
 
-        # Update the conversion methods
-        # Using setattr because mypy has a false positive
-        # https://github.com/python/mypy/issues/2427
-        setattr(schema_scalar, "serialize", scalar.serialize)
-        setattr(schema_scalar, "parse_value", scalar.parse_value)
-        setattr(schema_scalar, "parse_literal", scalar.parse_literal)
+        update_schema_scalar(schema, scalar.name, scalar)

tests/custom_scalars/test_money.py

@@ -21,7 +21,7 @@
 
 from gql import Client, gql
 from gql.transport.exceptions import TransportQueryError
-from gql.utilities import update_schema_scalars
+from gql.utilities import update_schema_scalar, update_schema_scalars
 from gql.variable_values import serialize_value
 
 from ..conftest import MS
@@ -623,7 +623,8 @@ async def test_update_schema_scalars(event_loop, aiohttp_server):
 
         # Update the schema MoneyScalar default implementation from
         # introspection with our provided conversion methods
-        update_schema_scalars(session.client.schema, [MoneyScalar])
+        # update_schema_scalars(session.client.schema, [MoneyScalar])
+        update_schema_scalar(session.client.schema, "Money", MoneyScalar)
 
         query = gql("query myquery($money: Money) {toEuros(money: $money)}")
 
@@ -639,17 +640,24 @@ async def test_update_schema_scalars(event_loop, aiohttp_server):
 
 def test_update_schema_scalars_invalid_scalar():
 
-    with pytest.raises(GraphQLError) as exc_info:
+    with pytest.raises(TypeError) as exc_info:
         update_schema_scalars(schema, [int])
 
     exception = exc_info.value
 
     assert str(exception) == "Scalars should be instances of GraphQLScalarType."
 
+    with pytest.raises(TypeError) as exc_info:
+        update_schema_scalar(schema, "test", int)
+
+    exception = exc_info.value
+
+    assert str(exception) == "Scalars should be instances of GraphQLScalarType."
+
 
 def test_update_schema_scalars_invalid_scalar_argument():
 
-    with pytest.raises(GraphQLError) as exc_info:
+    with pytest.raises(TypeError) as exc_info:
         update_schema_scalars(schema, MoneyScalar)
 
     exception = exc_info.value
@@ -661,12 +669,24 @@ def test_update_schema_scalars_scalar_not_found_in_schema():
 
     NotFoundScalar = GraphQLScalarType(name="abcd",)
 
-    with pytest.raises(GraphQLError) as exc_info:
+    with pytest.raises(KeyError) as exc_info:
         update_schema_scalars(schema, [MoneyScalar, NotFoundScalar])
 
     exception = exc_info.value
 
-    assert str(exception) == "Scalar 'abcd' not found in schema."
+    assert "Scalar 'abcd' not found in schema." in str(exception)
+
+
+def test_update_schema_scalars_scalar_type_is_not_a_scalar_in_schema():
+
+    with pytest.raises(TypeError) as exc_info:
+        update_schema_scalar(schema, "CountriesBalance", MoneyScalar)
+
+    exception = exc_info.value
+
+    assert 'The type "CountriesBalance" is not a GraphQLScalarType, it is a' in str(
+        exception
+    )
 
 
 @pytest.mark.asyncio