Serializing native Python enums does not work

[wichert]

Currently using SQL enums works well, unless you use a enum.Enum as base for the enum. For example using this model:

class Hairkind(enum.Enum):
    LONG = 'long'
    SHORT = 'short'

class Pet(Base):
    __tablename__ = 'pets'
    id = Column(Integer(), primary_key=True)
    hair_kind = Column(Enum(Hairkind, name='hair_kind'), nullable=False)

will fail badly if you try to query the hairKind field:

  File "lib/python3.7/site-packages/graphql/execution/executor.py", line 622, in complete_leaf_value
    path=path,
graphql.error.base.GraphQLError: Expected a value of type "hair_kind" but received: Hairkind.LONG

[wichert]

What is happening here is that graphqln_sqlalchemy.converter.convert_sqlalchemy_type.register creates a GraphQL Enum using the enum instances using items = type.enum_class.__members__.items(). But in graphql.type.definition.GraphQLEnumType.serialize this happens:

    def serialize(self, value):
        # type: (Union[str, PyEnum]) -> Optional[str]
        if isinstance(value, PyEnum):
            # We handle PyEnum values
            value = value.value
        if isinstance(value, collections.Hashable):
            enum_value = self._value_lookup.get(value)
            if enum_value:
                return enum_value.name

        return None

at that point the enum.Enum instance is converted to its value, which is then looked up. But the lookup table has the enum instances, causing the lookup to fail and an error to be returned.

[wichert]

This diff adds a failing test demonstrating the problem:

diff --git a/graphene_sqlalchemy/tests/models.py b/graphene_sqlalchemy/tests/models.py
index be7d5cd..3ba23a8 100644
--- a/graphene_sqlalchemy/tests/models.py
+++ b/graphene_sqlalchemy/tests/models.py
@@ -6,6 +6,12 @@ from sqlalchemy import Column, Date, Enum, ForeignKey, Integer, String, Table
 from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy.orm import mapper, relationship
 
+
+class Hairkind(enum.Enum):
+    LONG = 'long'
+    SHORT = 'short'
+
+
 Base = declarative_base()
 
 association_table = Table(
@@ -27,6 +33,7 @@ class Pet(Base):
     id = Column(Integer(), primary_key=True)
     name = Column(String(30))
     pet_kind = Column(Enum("cat", "dog", name="pet_kind"), nullable=False)
+    hair_kind = Column(Enum(Hairkind, name="hair_kind"), nullable=False)
     reporter_id = Column(Integer(), ForeignKey("reporters.id"))
 
 
diff --git a/graphene_sqlalchemy/tests/test_query.py b/graphene_sqlalchemy/tests/test_query.py
index f8bc840..2e2d602 100644
--- a/graphene_sqlalchemy/tests/test_query.py
+++ b/graphene_sqlalchemy/tests/test_query.py
@@ -9,7 +9,7 @@ from ..registry import reset_global_registry
 from ..fields import SQLAlchemyConnectionField
 from ..types import SQLAlchemyObjectType
 from ..utils import sort_argument_for_model, sort_enum_for_model
-from .models import Article, Base, Editor, Pet, Reporter
+from .models import Article, Base, Editor, Pet, Reporter, Hairkind
 
 db = create_engine("sqlite:///test_sqlalchemy.sqlite3")
 
@@ -34,7 +34,7 @@ def session():
 
 
 def setup_fixtures(session):
-    pet = Pet(name="Lassie", pet_kind="dog")
+    pet = Pet(name="Lassie", pet_kind="dog", hair_kind=Hairkind.LONG)
     session.add(pet)
     reporter = Reporter(first_name="ABA", last_name="X")
     session.add(reporter)
@@ -105,6 +105,7 @@ def test_should_query_enums(session):
           pet {
             name,
             petKind
+            hairKind
           }
         }
     """
@@ -326,9 +327,9 @@ def test_should_mutate_well(session):
 
 def sort_setup(session):
     pets = [
-        Pet(id=2, name="Lassie", pet_kind="dog"),
-        Pet(id=22, name="Alf", pet_kind="cat"),
-        Pet(id=3, name="Barf", pet_kind="dog"),
+        Pet(id=2, name="Lassie", pet_kind="dog", hair_kind=Hairkind.LONG),
+        Pet(id=22, name="Alf", pet_kind="cat", hair_kind=Hairkind.LONG),
+        Pet(id=3, name="Barf", pet_kind="dog", hair_kind=Hairkind.LONG),
     ]
     session.add_all(pets)
     session.commit()

[wichert]

The situation turns out to be worse now than with the last release. With the previous release you could add a resolver, like so:

    def resolve_type(self, info):
        return self.type.name

that workaround no longer works now, since graphql now expects to receive an enum and aborts when it gets a string instead.

[congocongo]

look at:
graphql-python/graphql-core#199

[robjampar]

Yeah this has broken enums in one of my libraries and the only way i can fix it is to monkey patch the method!

id suggest a non breaking change, for example:

def serialize(self, value):
    if isinstance(value, collections.Hashable):
        if value in self._value_lookup:
            enum_value = self._value_lookup.get(value)
    
        elif isinstance(value, PyEnum):
            # We handle PyEnum values
            enum_value = self._value_lookup.get(value.value)
    
        if enum_value:
            return enum_value.name
    
    return None```

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