Re-add default value for Field.

graphene/types/field.py

@@ -2,6 +2,8 @@ import inspect
 from collections import Mapping, OrderedDict
 from functools import partial
 
+from promise import Promise
+
 from ..utils.orderedtype import OrderedType
 from .argument import to_arguments
 from .structures import NonNull
@@ -18,7 +20,8 @@ class Field(OrderedType):
 
     def __init__(self, type, args=None, resolver=None, source=None,
                  deprecation_reason=None, name=None, description=None,
-                 required=False, _creation_counter=None, **extra_args):
+                 required=False, _creation_counter=None, default_value=None,
+                 **extra_args):
         super(Field, self).__init__(_creation_counter=_creation_counter)
         assert not args or isinstance(args, Mapping), (
             'Arguments in a field have to be a mapping, received "{}".'
@@ -27,7 +30,7 @@ class Field(OrderedType):
             'A Field cannot have a source and a resolver in at the same time.'
         )
 
-        if required:
+        if required or default_value is not None:
             type = NonNull(type)
 
         self.name = name
@@ -38,6 +41,7 @@ class Field(OrderedType):
         self.resolver = resolver
         self.deprecation_reason = deprecation_reason
         self.description = description
+        self.default_value = default_value
 
     @property
     def type(self):
@@ -46,4 +50,14 @@ class Field(OrderedType):
         return self._type
 
     def get_resolver(self, parent_resolver):
-        return self.resolver or parent_resolver
+        resolver = self.resolver or parent_resolver
+
+        def default_resolve(result):
+            return self.default_value if result is None else result
+
+        def defualt_resolver(self, *args, **kwargs):
+            return Promise.resolve(
+                resolver(*args, **kwargs)
+            ).then(default_resolve)
+
+        return defualt_resolver if self.default_value is not None else resolver

graphene/types/tests/test_field.py

@@ -16,19 +16,22 @@ def test_field_basic():
     resolver = lambda: None
     deprecation_reason = 'Deprecated now'
     description = 'My Field'
+    my_default='something'
     field = Field(
         MyType,
         name='name',
         args=args,
         resolver=resolver,
         description=description,
-        deprecation_reason=deprecation_reason
+        deprecation_reason=deprecation_reason,
+        default_value=my_default,
     )
     assert field.name == 'name'
     assert field.args == args
     assert field.resolver == resolver
     assert field.deprecation_reason == deprecation_reason
     assert field.description == description
+    assert field.default_value == my_default
 
 
 def test_field_required():

graphene/types/tests/test_query.py

@@ -1,9 +1,10 @@
 import json
 from functools import partial
 
-from graphql import execute, Source, parse
+from graphql import execute, Source, parse, GraphQLError
 
 from ..objecttype import ObjectType
+from ..field import Field
 from ..inputfield import InputField
 from ..inputobjecttype import InputObjectType
 from ..scalars import String, Int
@@ -22,6 +23,35 @@ def test_query():
     assert executed.data == {'hello': 'World'}
 
 
+def test_query_default_value():
+    class MyType(ObjectType):
+        field = String()
+
+    class Query(ObjectType):
+        hello = Field(MyType, default_value=MyType(field='something else!'))
+
+    hello_schema = Schema(Query)
+
+    executed = hello_schema.execute('{ hello { field } }')
+    assert not executed.errors
+    assert executed.data == {'hello': {'field': 'something else!'}}
+
+
+def test_query_wrong_default_value():
+    class MyType(ObjectType):
+        field = String()
+
+    class Query(ObjectType):
+        hello = Field(MyType, default_value='hello')
+
+    hello_schema = Schema(Query)
+
+    executed = hello_schema.execute('{ hello { field } }')
+    assert len(executed.errors) == 1
+    assert executed.errors[0].message == GraphQLError('Expected value of type "MyType" but got: str.').message
+    assert executed.data is None
+
+
 def test_query_resolve_function():
     class Query(ObjectType):
         hello = String()