Custom Types

Baeta generates a src/modules/types.ts file that lets you customize the TypeScript types used throughout your resolvers. This file acts as the bridge between your application's types and the generated GraphQL types.

The Types File

The generated file looks like this:

// src/modules/types.ts
import type { GraphQLResolveInfo } from "graphql";
import type { BaseObjectTypes, BaseScalars } from "../__generated__/utility.ts";
import type { Context } from "../types/context.ts";

export interface Scalars extends BaseScalars {}

export interface ObjectTypes extends BaseObjectTypes {}

export type Ctx = Context;

export type Info = GraphQLResolveInfo;

Each section controls a different aspect of type safety in your resolvers.

Object Types

The ObjectTypes interface lets you override the source type (also known as the parent or root type) for any GraphQL object type. This is especially useful when your data source returns a different shape than your GraphQL schema.

By default, each object type's source is inferred from the GraphQL schema. When you override it, resolvers for that type will receive your custom type as source instead.

Example: Using Prisma Models

When using Prisma, the database model often differs from the GraphQL type. Use ObjectTypes to tell Baeta about the real shape of your data:

import type { BaseObjectTypes, BaseScalars } from "../__generated__/utility.ts";
import type { User, UserPhoto } from "../lib/db/prisma.ts";
import type { Context } from "../types/context.ts";

export interface ObjectTypes extends BaseObjectTypes {
  User: User; // Resolvers for User fields will receive Prisma's User as source
  UserPhoto: UserPhoto;
}

Now in your resolvers, source is typed as the Prisma model:

const { User } = UserModule;

// source is typed as Prisma's User model, not the GraphQL User type
const userResolver = User.$fields({
  id: User.id.key("id"),
  email: User.email.key("email"),
  // Compute GraphQL fields from the Prisma model
  name: User.name.resolve(({ source }) => `${source.firstName} ${source.lastName}`),
  photos: User.photos.resolve(async ({ source }) => {
    return db.photo.findMany({ where: { userId: source.id } });
  }),
});

tip

This is particularly useful when your database model has fields that don't exist in the GraphQL schema, or when field names differ between your data source and your API.

Scalars

The Scalars interface lets you map custom GraphQL scalars to TypeScript types. See the Scalars guide for more details.

export interface Scalars extends BaseScalars {
  DateTime: Date;
  UUID: `${string}-${string}-${string}-${string}-${string}`;
}

Context

The Ctx type alias defines the context type available in all resolvers and middlewares. See the Context guide for more details.

import type { Context } from "../types/context.ts";

export type Ctx = Context;

Info

The Info type alias defines the GraphQL resolve info type. This defaults to GraphQLResolveInfo but can be overridden if you use a library that extends it.

import type { GraphQLResolveInfo } from "graphql";

export type Info = GraphQLResolveInfo;