feat(wrap): allow making the new field type Nullable

Author: Mustafa Mansour

packages/wrap/src/transforms/WrapFields.ts

@@ -34,6 +34,10 @@ interface WrapFieldsTransformationContext {
   paths: Record<string, { pathToField: Array<string>; alias: string }>;
 }
 
+interface WrapFieldsConfig {
+  isNullable?: boolean;
+}
+
 export default class WrapFields<TContext extends Record<string, any>>
   implements Transform<WrapFieldsTransformationContext, TContext>
 {
@@ -43,19 +47,22 @@ export default class WrapFields<TContext extends Record<string, any>>
   private readonly numWraps: number;
   private readonly fieldNames: Array<string> | undefined;
   private readonly transformer: MapFields<TContext>;
+  private readonly config: WrapFieldsConfig;
 
   constructor(
     outerTypeName: string,
     wrappingFieldNames: Array<string>,
     wrappingTypeNames: Array<string>,
     fieldNames?: Array<string>,
     prefix = 'gqtld',
+    config: WrapFieldsConfig = { isNullable: false },
   ) {
     this.outerTypeName = outerTypeName;
     this.wrappingFieldNames = wrappingFieldNames;
     this.wrappingTypeNames = wrappingTypeNames;
     this.numWraps = wrappingFieldNames.length;
     this.fieldNames = fieldNames;
+    this.config = config;
 
     const remainingWrappingFieldNames = this.wrappingFieldNames.slice();
     const outerMostWrappingFieldName = remainingWrappingFieldNames.shift();
@@ -167,9 +174,11 @@ export default class WrapFields<TContext extends Record<string, any>>
       resolve = defaultMergedResolver;
     }
 
-    const wrappingType = new GraphQLNonNull(
-      newSchema.getType(wrappingTypeName) as GraphQLObjectType,
-    );
+    const baseType = newSchema.getType(wrappingTypeName) as GraphQLObjectType;
+    const wrappingType = this.config.isNullable
+      ? baseType
+      : new GraphQLNonNull(baseType);
+
     const newFieldConfig: GraphQLFieldConfig<any, any> =
       wrappingOperation === 'subscription'
         ? {

packages/wrap/tests/transformWrapFields.test.ts

@@ -1,6 +1,6 @@
 import { makeExecutableSchema } from '@graphql-tools/schema';
 import { WrapFields, wrapSchema } from '@graphql-tools/wrap';
-import { graphql, GraphQLObjectType } from 'graphql';
+import { graphql, GraphQLObjectType, isNullableType } from 'graphql';
 import { describe, expect, test } from 'vitest';
 
 describe('WrapFields', () => {
@@ -44,7 +44,9 @@ describe('WrapFields', () => {
   test('schema is transformed with new type and field', async () => {
     const userType = schema.getType('User') as GraphQLObjectType;
     const addressType = schema.getType('Address') as GraphQLObjectType;
+    const addressField = userType.getFields()['address'];
 
+    expect(isNullableType(addressField?.type)).toBe(false);
     expect(userType.getFields()['address']).toBeDefined();
     expect(Object.keys(addressType.getFields()).sort()).toEqual([
       'city',
@@ -53,6 +55,27 @@ describe('WrapFields', () => {
     ]);
   });
 
+  test('new field is nullable if specified', async () => {
+    const schema = wrapSchema({
+      schema: subschema,
+      transforms: [
+        new WrapFields(
+          'User',
+          ['address'],
+          ['Address'],
+          ['street', 'city', 'zipcode'],
+          undefined,
+          { isNullable: true },
+        ),
+      ],
+    });
+
+    const userType = schema.getType('User') as GraphQLObjectType;
+    const addressField = userType.getFields()['address'];
+
+    expect(isNullableType(addressField?.type)).toBe(true);
+  });
+
   test('select fields are wrapped and queryable', async () => {
     const result = await graphql({
       schema,