feat(mapSchema): initial version

mapSchema enables transformation of schema objects without modification of the original schema.

See graphql/graphql-js#1199

src/test/testMapSchema.ts

@@ -0,0 +1,64 @@
+import { expect } from 'chai';
+import { GraphQLSchema, GraphQLObjectType, graphqlSync } from 'graphql';
+
+import { makeExecutableSchema, mapSchema } from '../index';
+import { MapperKind } from '../utils/map';
+
+describe('mapSchema', () => {
+  it('does not throw', () => {
+    const schema = makeExecutableSchema({
+      typeDefs: `
+        type Query {
+          version: String
+        }
+      `,
+    });
+
+    const newSchema = mapSchema(schema, {});
+    expect(newSchema).to.be.instanceOf(GraphQLSchema);
+  });
+
+  it('can add a resolver', () => {
+    const schema = makeExecutableSchema({
+      typeDefs: `
+        type Query {
+          version: Int
+        }
+      `,
+    });
+
+    const newSchema = mapSchema(schema, {
+      [MapperKind.QUERY]: type => {
+        const queryConfig = type.toConfig();
+        queryConfig.fields.version.resolve = () => 1;
+        return new GraphQLObjectType(queryConfig);
+      },
+    });
+
+    expect(newSchema).to.be.instanceOf(GraphQLSchema);
+
+    const result = graphqlSync(newSchema, '{ version }');
+    expect(result.data.version).to.equal(1);
+  });
+
+  it('can change the root query name', () => {
+    const schema = makeExecutableSchema({
+      typeDefs: `
+        type Query {
+          version: Int
+        }
+      `,
+    });
+
+    const newSchema = mapSchema(schema, {
+      [MapperKind.QUERY]: type => {
+        const queryConfig = type.toConfig();
+        queryConfig.name = 'RootQuery';
+        return new GraphQLObjectType(queryConfig);
+      },
+    });
+
+    expect(newSchema).to.be.instanceOf(GraphQLSchema);
+    expect(newSchema.getQueryType().name).to.equal('RootQuery');
+  });
+});

src/utils/index.ts

@@ -27,3 +27,4 @@ export {
 export { appendFields, removeFields } from './fields';
 export { createNamedStub } from './stub';
 export { graphqlVersion } from './graphqlVersion';
+export { mapSchema } from './map';