Extending tRPC Functionality
Discover advanced ways to extend tRPC with custom builders, plugins, and integration with other libraries.
Extending tRPC Functionality is a free tRPC End-to-End Type Safe APIs lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the tRPC End-to-End Type Safe APIs learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Extend tRPC's Core
tRPC is incredibly powerful out-of-the-box, but sometimes your application needs more custom control and specialized behavior. This lesson will show you how to extend tRPC beyond basic middleware.
We'll explore custom procedure builders for creating specialized API endpoints and discuss how to integrate tRPC seamlessly with other libraries like ORMs.
Why Custom Builders?
Standard middleware is great for applying common logic to all or a group of procedures, such as authentication or logging.
But what if you need to define specific types of procedures, like adminProcedure or publicProcedure, each with unique context properties or pre-configured middleware chains? Custom procedure builders are perfect for this!
Crafting a Builder with `createBuilder`
tRPC provides the createBuilder utility to help you define your own procedure factory. This builder can extend the context (ctx), add metadata, or apply middleware automatically to any procedure built with it.
It allows you to abstract common setup logic into a reusable pattern, making your API definitions cleaner and more consistent.
Builder Example: Admin Procedure
Let's create an adminProcedure. This builder ensures the user is not only logged in (via protectedProcedure) but also has an isAdmin flag set in their context. This logic is then automatically applied to any procedure using adminProcedure.
// Minimal tRPC-like setup for demonstration
type Context = { user?: { id: number; isAdmin?: boolean } };
const mockProcedure = {
use: (middleware: any) => ({
use: (nextMiddleware: any) => ({
_isBuilder: true,
_middlewares: [middleware, nextMiddleware]
}),
_isBuilder: true,
_middlewares: [middleware]
}),
_isBuilder: true,
_middlewares: []
};
const t = {
procedure: mockProcedure
};
// --- Actual tRPC Builder Code ---
const protectedProcedure = t.procedure.use(async ({ ctx, next }: any) => {
if (!ctx.user) {
throw new Error('Not authenticated');
}
return next({ ctx: { ...ctx, user: ctx.user } });
});
const adminProcedure = protectedProcedure.use(async ({ ctx, next }: any) => {
if (!ctx.user?.isAdmin) {
throw new Error('Not an admin!');
}
return next({ ctx: { ...ctx, user: ctx.user } });
});
console.log("Protected procedure builder defined.");
console.log("Admin procedure builder defined.");
console.log("Admin procedure has " + adminProcedure._middlewares.length + " middlewares.");Benefits of Custom Builders
Custom builders offer several significant advantages:
- Reusability: Define complex logic once and apply it across many procedures.
- Type Safety: Enforce specific context types for groups of procedures.
- Readability: Procedures become self-documenting (e.g.,
adminProcedure.query(...)clearly indicates its requirements). - Consistency: Ensure all procedures of a certain type adhere to specific rules and checks.
Integration with External Libraries
tRPC is unopinionated about your data layer. This means you can easily integrate it with any ORM (like Prisma, Drizzle), database client, or external API service you prefer.
The key to this seamless integration is often to initialize instances of these clients and attach them to your tRPC context. This makes them readily available to all your procedures.
Contextualizing an ORM (Prisma)
A very common pattern in tRPC applications is to initialize your ORM client (e.g., Prisma Client) and then attach that instance to your tRPC context object.
This allows all your tRPC procedures to access the database client via ctx.prisma, centralizing its management and providing type safety.
// Minimal tRPC-like setup for demonstration
type MockPrismaClient = {
user: {
findUnique: (args: { where: { id: number } }) => { id: number; name: string } | null;
};
};
type ContextWithPrisma = {
prisma: MockPrismaClient;
};
const mockProcedure = {
query: (handler: (opts: { ctx: ContextWithPrisma }) => any) => ({
_handler: handler,
_isQuery: true
})
};
const t = {
procedure: mockProcedure
};
// --- Actual tRPC Context Integration ---
const publicProcedure = t.procedure;
const getUserProcedure = publicProcedure.query(async ({ ctx }) => {
const user = await ctx.prisma.user.findUnique({ where: { id: 1 } });
return user ? `User name: ${user.name}` : 'User not found.';
});
// --- Demonstration (conceptual execution) ---
const mockPrisma: MockPrismaClient = {
user: {
findUnique: (args) => {
if (args.where.id === 1) {
return { id: 1, name: 'Alice' };
}
return null;
}
}
};
const mockContext: ContextWithPrisma = { prisma: mockPrisma };
console.log("Prisma client attached to context type.");
console.log("Conceptual handler output for user 1:");
console.log(await getUserProcedure._handler({ ctx: mockContext }));The Power of Plugins (Conceptual)
Beyond builders, tRPC offers an experimental createTRPCPlugin API. Plugins provide even deeper hooks into tRPC's internals, allowing you to customize error formatting, add custom data transformers, or modify the request lifecycle in advanced ways.
They are designed for truly complex, core-level extensions that affect how tRPC operates at a foundational level.
When to Use What?
Choosing between custom builders and plugins depends on your extension needs:
- Custom Builders: Best for defining specific types of procedures, enriching the context object, or applying common middleware chains. They operate at the procedure definition level.
- Plugins: Ideal for modifying tRPC's core behavior, such as custom error handling, data serialization/deserialization, or integrating with external systems at a global, foundational level.
Quick Check
Which of the following are key benefits of using custom tRPC procedure builders?
Summary of Extensions
In this lesson, we explored how to extend tRPC's capabilities. We learned to use custom procedure builders to create specialized, reusable procedures like adminProcedure, enhancing reusability, type safety, and consistency.
We also saw how to integrate external libraries like ORMs by attaching them to the tRPC context. Finally, we touched upon the advanced potential of tRPC plugins for deeper core modifications. These tools empower you to tailor tRPC to your application's unique needs.
Frequently asked questions
Is the “Extending tRPC Functionality” lesson free?
Yes — the full text of “Extending tRPC Functionality” is free to read here on the web, and the tRPC End-to-End Type Safe APIs course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the tRPC End-to-End Type Safe APIs course, upgrade to CoddyKit PRO.
What will I learn in “Extending tRPC Functionality”?
Discover advanced ways to extend tRPC with custom builders, plugins, and integration with other libraries. You practise tRPC End-to-End Type Safe APIs with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start tRPC End-to-End Type Safe APIs?
No prior experience is required. tRPC End-to-End Type Safe APIs on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Extending tRPC Functionality” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this tRPC End-to-End Type Safe APIs lesson?
Yes. Every tRPC End-to-End Type Safe APIs lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Setting Up a tRPC Monorepo
- Code Sharing and Reusability
- Extending tRPC Functionality
- Versioning and Publishing Shared tRPC Packages