[RFC] Allows use of generated schemas for execution. (#469)

Right now our generated schemas (built from introspection, built from AST) explicitly do not allow their use in execution. They throw as soon as any resolver function is called. This conservative behavior was appropriate for early versions where we wanted to limit the surface area under use. Today it's becoming more clear that there are immediately valuable use cases for using generated schema in execution.

Author: leebyron

src/type/definition.js

@@ -704,7 +704,7 @@ export type GraphQLUnionTypeConfig = {
    * the default implementation will call `isTypeOf` on each implementing
    * Object type.
    */
-  resolveType?: GraphQLTypeResolveFn;
+  resolveType?: ?GraphQLTypeResolveFn;
   description?: ?string;
 };
 

src/utilities/__tests__/buildASTSchema-test.js

@@ -13,10 +13,11 @@ import { parse } from '../../language';
 import { printSchema } from '../schemaPrinter';
 import { buildASTSchema } from '../buildASTSchema';
 import {
+  graphql,
   GraphQLSkipDirective,
   GraphQLIncludeDirective,
   GraphQLDeprecatedDirective,
-} from '../../type/directives';
+} from '../../';
 
 /**
  * This function does a full cycle of going from a
@@ -32,6 +33,23 @@ function cycleOutput(body) {
 }
 
 describe('Schema Builder', () => {
+
+  it('can use built schema for limited execution', async () => {
+    const schema = buildASTSchema(parse(`
+      schema { query: Query }
+      type Query {
+        str: String
+      }
+    `));
+
+    const result = await graphql(
+      schema,
+      '{ str }',
+      { str: 123 }
+    );
+    expect(result.data).to.deep.equal({ str: '123' });
+  });
+
   it('Simple type', () => {
     const body = `
 schema {

src/utilities/__tests__/buildClientSchema-test.js

@@ -644,7 +644,7 @@ describe('Type System: build schema from introspection', () => {
     await testSchema(schema);
   });
 
-  it('cannot use client schema for general execution', async () => {
+  it('can use client schema for limited execution', async () => {
     const customScalar = new GraphQLScalarType({
       name: 'CustomScalar',
       serialize: () => null,
@@ -670,20 +670,13 @@ describe('Type System: build schema from introspection', () => {
 
     const result = await graphql(
       clientSchema,
-      'query NoNo($v: CustomScalar) { foo(custom1: 123, custom2: $v) }',
-      { foo: 'bar' },
+      'query Limited($v: CustomScalar) { foo(custom1: 123, custom2: $v) }',
+      { foo: 'bar', unused: 'value' },
       null,
       { v: 'baz' }
     );
-    expect(result).to.containSubset({
-      data: {
-        foo: null,
-      },
-      errors: [
-        { message: 'Client Schema cannot be used for execution.',
-          locations: [ { line: 1, column: 32 } ] }
-      ]
-    });
+
+    expect(result.data).to.deep.equal({ foo: 'bar' });
   });
 
   describe('throws when given incomplete introspection', () => {

src/utilities/__tests__/extendSchema-test.js

@@ -115,7 +115,7 @@ describe('extendSchema', () => {
     expect(printSchema(testSchema)).to.not.contain('newField');
   });
 
-  it('cannot be used for execution', async () => {
+  it('can be used for limited execution', async () => {
     const ast = parse(`
       extend type Query {
         newField: String
@@ -124,11 +124,12 @@ describe('extendSchema', () => {
     const extendedSchema = extendSchema(testSchema, ast);
     const clientQuery = parse('{ newField }');
 
-    const result = await execute(extendedSchema, clientQuery);
-    expect(result.data.newField).to.equal(null);
-    expect(result.errors).to.containSubset([ {
-      message: 'Client Schema cannot be used for execution.'
-    } ]);
+    const result = await execute(
+      extendedSchema,
+      clientQuery,
+      { newField: 123 }
+    );
+    expect(result.data).to.deep.equal({ newField: '123' });
   });
 
   it('can describe the extended fields', async () => {

src/utilities/buildASTSchema.js

@@ -405,8 +405,8 @@ export function buildASTSchema(ast: Document): GraphQLSchema {
     return new GraphQLInterfaceType({
       name: typeName,
       description: getDescription(def),
-      resolveType: () => null,
       fields: () => makeFieldDefMap(def),
+      resolveType: cannotExecuteSchema,
     });
   }
 
@@ -431,8 +431,8 @@ export function buildASTSchema(ast: Document): GraphQLSchema {
     return new GraphQLUnionType({
       name: def.name.value,
       description: getDescription(def),
-      resolveType: () => null,
       types: def.types.map(t => produceObjectType(t)),
+      resolveType: cannotExecuteSchema,
     });
   }
 
@@ -517,3 +517,9 @@ function leadingSpaces(str) {
   }
   return i;
 }
+
+function cannotExecuteSchema() {
+  throw new Error(
+    'Generated Schema cannot use Interface or Union types for execution.'
+  );
+}

src/utilities/buildClientSchema.js

@@ -226,7 +226,7 @@ export function buildClientSchema(
     return new GraphQLScalarType({
       name: scalarIntrospection.name,
       description: scalarIntrospection.description,
-      serialize: () => null,
+      serialize: id => id,
       // Note: validation calls the parse functions to determine if a
       // literal value is correct. Returning null would cause use of custom
       // scalars to always fail validation. Returning false causes them to
@@ -305,7 +305,6 @@ export function buildClientSchema(
         deprecationReason: fieldIntrospection.deprecationReason,
         type: getOutputType(fieldIntrospection.type),
         args: buildInputValueDefMap(fieldIntrospection.args),
-        resolve: cannotExecuteClientSchema,
       })
     );
   }
@@ -393,5 +392,7 @@ export function buildClientSchema(
 }
 
 function cannotExecuteClientSchema() {
-  throw new Error('Client Schema cannot be used for execution.');
+  throw new Error(
+    'Client Schema cannot use Interface or Union types for execution.'
+  );
 }

src/utilities/extendSchema.js

@@ -350,6 +350,7 @@ export function extendSchema(
       description: type.description,
       interfaces: () => extendImplementedInterfaces(type),
       fields: () => extendFieldMap(type),
+      isTypeOf: type.isTypeOf,
     });
   }
 
@@ -360,7 +361,7 @@ export function extendSchema(
       name: type.name,
       description: type.description,
       fields: () => extendFieldMap(type),
-      resolveType: cannotExecuteClientSchema,
+      resolveType: type.resolveType,
     });
   }
 
@@ -369,7 +370,7 @@ export function extendSchema(
       name: type.name,
       description: type.description,
       types: type.getTypes().map(getTypeFromDef),
-      resolveType: cannotExecuteClientSchema,
+      resolveType: type.resolveType,
     });
   }
 
@@ -409,7 +410,7 @@ export function extendSchema(
         deprecationReason: field.deprecationReason,
         type: extendFieldType(field.type),
         args: keyMap(field.args, arg => arg.name),
-        resolve: cannotExecuteClientSchema,
+        resolve: field.resolve,
       };
     });
 
@@ -430,7 +431,6 @@ export function extendSchema(
             description: getDescription(field),
             type: buildOutputFieldType(field.type),
             args: buildInputValues(field.arguments),
-            resolve: cannotExecuteClientSchema,
           };
         });
       });
@@ -475,7 +475,7 @@ export function extendSchema(
       name: typeAST.name.value,
       description: getDescription(typeAST),
       fields: () => buildFieldMap(typeAST),
-      resolveType: cannotExecuteClientSchema,
+      resolveType: cannotExecuteExtendedSchema,
     });
   }
 
@@ -484,15 +484,15 @@ export function extendSchema(
       name: typeAST.name.value,
       description: getDescription(typeAST),
       types: typeAST.types.map(getObjectTypeFromAST),
-      resolveType: cannotExecuteClientSchema,
+      resolveType: cannotExecuteExtendedSchema,
     });
   }
 
   function buildScalarType(typeAST: ScalarTypeDefinition) {
     return new GraphQLScalarType({
       name: typeAST.name.value,
       description: getDescription(typeAST),
-      serialize: () => null,
+      serialize: id => id,
       // Note: validation calls the parse functions to determine if a
       // literal value is correct. Returning null would cause use of custom
       // scalars to always fail validation. Returning false causes them to
@@ -543,7 +543,6 @@ export function extendSchema(
         type: buildOutputFieldType(field.type),
         description: getDescription(field),
         args: buildInputValues(field.arguments),
-        resolve: cannotExecuteClientSchema,
       })
     );
   }
@@ -588,6 +587,8 @@ export function extendSchema(
   }
 }
 
-function cannotExecuteClientSchema() {
-  throw new Error('Client Schema cannot be used for execution.');
+function cannotExecuteExtendedSchema() {
+  throw new Error(
+    'Extended Schema cannot use Interface or Union types for execution.'
+  );
 }