Adds support for resolving union/interface types when using a generated schema

Author: jonbretman

src/execution/execute.js

@@ -33,6 +33,7 @@ import type {
   GraphQLAbstractType,
   GraphQLField,
   GraphQLFieldResolver,
+  GraphQLTypeResolver,
   GraphQLResolveInfo,
   ResponsePath,
 } from '../type/definition';
@@ -91,6 +92,7 @@ export type ExecutionContext = {
   operation: OperationDefinitionNode;
   variableValues: {[key: string]: mixed};
   fieldResolver: GraphQLFieldResolver<any, any>;
+  typeResolver: GraphQLTypeResolver<any, any>;
   errors: Array<GraphQLError>;
 };
 
@@ -137,7 +139,8 @@ declare function execute(
   contextValue?: mixed,
   variableValues?: ?{[key: string]: mixed},
   operationName?: ?string,
-  fieldResolver?: ?GraphQLFieldResolver<any, any>
+  fieldResolver?: ?GraphQLFieldResolver<any, any>,
+  typeResolver?: ?GraphQLTypeResolver<any, any>
 ): Promise<ExecutionResult>;
 export function execute(
   argsOrSchema,
@@ -146,7 +149,8 @@ export function execute(
   contextValue,
   variableValues,
   operationName,
-  fieldResolver
+  fieldResolver,
+  typeResolver
 ) {
   // Extract arguments from object args if provided.
   return arguments.length === 1 ?
@@ -157,7 +161,8 @@ export function execute(
       argsOrSchema.contextValue,
       argsOrSchema.variableValues,
       argsOrSchema.operationName,
-      argsOrSchema.fieldResolver
+      argsOrSchema.fieldResolver,
+      typeResolver
     ) :
     executeImpl(
       argsOrSchema,
@@ -166,7 +171,8 @@ export function execute(
       contextValue,
       variableValues,
       operationName,
-      fieldResolver
+      fieldResolver,
+      typeResolver
     );
 }
 
@@ -177,7 +183,8 @@ function executeImpl(
   contextValue,
   variableValues,
   operationName,
-  fieldResolver
+  fieldResolver,
+  typeResolver
 ) {
   // If arguments are missing or incorrect, throw an error.
   assertValidExecutionArguments(
@@ -197,7 +204,8 @@ function executeImpl(
       contextValue,
       variableValues,
       operationName,
-      fieldResolver
+      fieldResolver,
+      typeResolver
     );
   } catch (error) {
     return Promise.resolve({ errors: [ error ] });
@@ -281,7 +289,8 @@ export function buildExecutionContext(
   contextValue: mixed,
   rawVariableValues: ?{[key: string]: mixed},
   operationName: ?string,
-  fieldResolver: ?GraphQLFieldResolver<any, any>
+  fieldResolver: ?GraphQLFieldResolver<any, any>,
+  typeResolver: ?GraphQLTypeResolver<any, any>,
 ): ExecutionContext {
   const errors: Array<GraphQLError> = [];
   let operation: ?OperationDefinitionNode;
@@ -330,6 +339,7 @@ export function buildExecutionContext(
     operation,
     variableValues,
     fieldResolver: fieldResolver || defaultFieldResolver,
+    typeResolver: typeResolver || defaultTypeResolver,
     errors,
   };
 }
@@ -1037,9 +1047,9 @@ function completeAbstractValue(
   path: ResponsePath,
   result: mixed
 ): mixed {
-  const runtimeType = returnType.resolveType ?
-    returnType.resolveType(result, exeContext.contextValue, info) :
-    defaultResolveTypeFn(result, exeContext.contextValue, info, returnType);
+  const runtimeType = exeContext.typeResolver(
+    result, exeContext, info, returnType
+  );
 
   const promise = getPromise(runtimeType);
   if (promise) {
@@ -1256,6 +1266,17 @@ function (source, args, context, info) {
   }
 };
 
+export const defaultTypeResolver: GraphQLTypeResolver<any, *> =
+function (result, context, info, returnType) {
+  if (result && result.__typename) {
+    return result.__typename;
+  }
+
+  return returnType.resolveType ?
+    returnType.resolveType(result, context.contextValue, info) :
+    defaultResolveTypeFn(result, context.contextValue, info, returnType);
+};
+
 /**
  * Only returns the value if it acts like a Promise, i.e. has a "then" function,
  * otherwise returns void.

src/type/definition.js

@@ -614,7 +614,8 @@ export type GraphQLObjectTypeConfig<TSource, TContext> = {
 export type GraphQLTypeResolver<TSource, TContext> = (
   value: TSource,
   context: TContext,
-  info: GraphQLResolveInfo
+  info: GraphQLResolveInfo,
+  returnValue: any
 ) => ?GraphQLObjectType | string | Promise<?GraphQLObjectType | string>;
 
 export type GraphQLIsTypeOfFn<TSource, TContext> = (

src/utilities/__tests__/buildASTSchema-test.js

@@ -394,6 +394,137 @@ describe('Schema Builder', () => {
     expect(output).to.equal(body);
   });
 
+  it('Specifying Union type using __typename', async () => {
+    const schema = buildSchema(`
+      schema {
+        query: Root
+      }
+
+      type Root {
+        fruits: [Fruit]
+      }
+
+      union Fruit = Apple | Banana
+
+      type Apple {
+        color: String
+      }
+
+      type Banana {
+        length: Int
+      }
+    `);
+
+    const query = `
+      {
+        fruits {
+          ... on Apple {
+            color
+          }
+          ... on Banana {
+            length
+          }
+        }
+      }
+    `;
+
+    const root = {
+      fruits: [
+        {
+          color: 'green',
+          __typename: 'Apple',
+        },
+        {
+          length: 5,
+          __typename: 'Banana',
+        }
+      ]
+    };
+
+    expect(await graphql(schema, query, root)).to.deep.equal({
+      data: {
+        fruits: [
+          {
+            color: 'green',
+          },
+          {
+            length: 5,
+          }
+        ]
+      }
+    });
+  });
+
+  it('Specifying Interface type using __typename', async () => {
+    const schema = buildSchema(`
+      schema {
+        query: Root
+      }
+
+      type Root {
+        characters: [Character]
+      }
+
+      interface Character {
+        name: String!
+      }
+
+      type Human implements Character {
+        name: String!
+        totalCredits: Int
+      }
+
+      type Droid implements Character {
+        name: String!
+        primaryFunction: String
+      }
+    `);
+
+    const query = `
+      {
+        characters {
+          name
+          ... on Human {
+            totalCredits
+          }
+          ... on Droid {
+            primaryFunction
+          }
+        }
+      }
+    `;
+
+    const root = {
+      characters: [
+        {
+          name: 'Han Solo',
+          totalCredits: 10,
+          __typename: 'Human',
+        },
+        {
+          name: 'R2-D2',
+          primaryFunction: 'Astromech',
+          __typename: 'Droid',
+        }
+      ]
+    };
+
+    expect(await graphql(schema, query, root)).to.deep.equal({
+      data: {
+        characters: [
+          {
+            name: 'Han Solo',
+            totalCredits: 10,
+          },
+          {
+            name: 'R2-D2',
+            primaryFunction: 'Astromech',
+          }
+        ]
+      }
+    });
+  });
+
   it('Custom Scalar', () => {
     const body = dedent`
       schema {