support additional fields

README.md

@@ -288,6 +288,51 @@ expect(await AuthorFactory.build({ bookCount: 3 })).toStrictEqual({
 });
 ```
 
+### Additional Fields
+
+You can add additional fields to the data being built. This is useful when you want to build a fake data for a query that contains [aliases](https://graphql.org/learn/queries/#aliases), such as:
+
+```graphql
+query GetAuthorInfo {
+  author(id: '1') {
+    id
+    name
+    books {
+      id
+      title
+    }
+    popularBooks: books(popularOnly: true) {
+      id
+      title
+    }
+  }
+}
+```
+
+```ts
+import { defineAuthorFactory, type OptionalBook, dynamic } from '../__generated__/fabbrica';
+const AuthorFactory = defineAuthorFactory.withAdditionalFields<{ popularBooks: OptionalBook[] }>()({
+  defaultFields: {
+    id: dynamic(({ seq }) => `Author-${seq}`),
+    name: 'Komata Mikami',
+    // Generate a fake data for the `Author.books()` field
+    books: dynamic(() => BookFactory.buildList(3)),
+    // Generate a fake data for the `Author.books(popularOnly: true)` field
+    popularBooks: dynamic(() => BookFactory.buildList(1)),
+  },
+});
+expect(await AuthorFactory.build()).toStrictEqual({
+  id: 'Author-0',
+  name: 'Komata Mikami',
+  books: [
+    { id: 'Book-0', title: 'Yuyushiki Vol.0' },
+    { id: 'Book-1', title: 'Yuyushiki Vol.1' },
+    { id: 'Book-2', title: 'Yuyushiki Vol.2' },
+  ],
+  popularBooks: [{ id: 'Book-3', title: 'Yuyushiki Vol.3' }],
+});
+```
+
 ### Traits
 
 Traits allow you to group the default values of fields and apply them to factories.

e2e/esm/index.e2e.ts

@@ -1,4 +1,4 @@
-import { expect, it, describe, assertType, expectTypeOf, vi } from 'vitest';
+import { expect, it, describe, expectTypeOf, vi } from 'vitest';
 import {
   defineAuthorFactory,
   defineBookFactory,
@@ -16,6 +16,7 @@ import {
   defineNullableTest_TypeFactory,
   defineInputTest_InputFactory,
   defineNonOptionalDefaultFields_OptionalDefaultFieldsTypeFactory,
+  OptionalBook,
 } from './__generated__/1-basic/fabbrica.js';
 import { oneOf } from './test/util.js';
 import { definePrefixTypeFactory } from './__generated__/2-typesPrefix/fabbrica.js';
@@ -656,6 +657,39 @@ describe('defineTypeFactory', () => {
       expect(book2.id).toBe('Bar-Book');
     });
   });
+  it('additionalFields', async () => {
+    const AuthorFactory = defineAuthorFactory.withAdditionalFields<{ popularBooks: OptionalBook[] }>()({
+      defaultFields: {
+        id: dynamic(({ seq }) => `Author-${seq}`),
+        name: 'Komata Mikami',
+        books: dynamic(() => BookFactory.buildList(3)),
+        popularBooks: dynamic(() => BookFactory.buildList(1)),
+      },
+    });
+    const BookFactory = defineBookFactory({
+      defaultFields: {
+        id: dynamic(({ seq }) => `Book-${seq}`),
+        title: dynamic(({ seq }) => `Yuyushiki Vol.${seq}`),
+      },
+    });
+    const author = await AuthorFactory.build();
+    expect(author).toStrictEqual({
+      id: 'Author-0',
+      name: 'Komata Mikami',
+      books: [
+        { id: 'Book-0', title: 'Yuyushiki Vol.0' },
+        { id: 'Book-1', title: 'Yuyushiki Vol.1' },
+        { id: 'Book-2', title: 'Yuyushiki Vol.2' },
+      ],
+      popularBooks: [{ id: 'Book-3', title: 'Yuyushiki Vol.3' }],
+    });
+    expectTypeOf(author).toEqualTypeOf<{
+      id: string;
+      name: string;
+      books: { id: string; title: string }[];
+      popularBooks: { id: string; title: string }[];
+    }>();
+  });
   describe('resetAllSequence', () => {
     it('resets all sequence', async () => {
       const BookFactory = defineBookFactory({

src/helper/factory.ts

@@ -59,6 +59,10 @@ export interface DefineTypeFactoryInterfaceRequired<
   withTransientFields<NewTransientFields extends Record<string, unknown>>(
     defaultTransientFields: NewTransientFields,
   ): DefineTypeFactoryInterface<Type, Merge<TransientFields, NewTransientFields>>;
+  withAdditionalFields<AdditionalFields extends Record<string, unknown>>(): DefineTypeFactoryInterface<
+    Merge<Type, AdditionalFields>,
+    TransientFields
+  >;
 }
 
 export interface DefineTypeFactoryInterface<
@@ -180,5 +184,12 @@ class DefineTypeFactory<
     // eslint-disable-next-line @typescript-eslint/no-explicit-any
     return new DefineTypeFactory({ ...this._defaultTransientFields, ...defaultTransientFields }) as any;
   }
+  withAdditionalFields<AdditionalFields extends Record<string, unknown>>(): DefineTypeFactoryInterface<
+    Merge<Type, AdditionalFields>,
+    TransientFields
+  > {
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    return this as any;
+  }
 }
 export const defineTypeFactory = new DefineTypeFactory({}) as unknown as DefineTypeFactoryInterfaceRequired<{}, {}>;