tRPC End-to-End Type Safe APIs · Lesson

Implementing Query Procedures

Create read-only data fetching endpoints using tRPC query procedures with input and output types.

What are tRPC Queries?

Queries are like asking a question to your server. They are designed for fetching data, not changing it. Think of them as the "GET" requests in a traditional REST API.

Read-only: Queries should never change data on your server.
Idempotent: Running a query multiple times should produce the same result.
Cached: Clients can often cache query results for better performance.

They are the foundation for retrieving information in your tRPC application.

Defining a Simple Query

In tRPC, you define queries within a router using .query(). Let's look at the basic structure.

First, you need to initialize tRPC (usually done once in your server setup):

const t = initTRPC.create();

Then, define your router and add a query:

import { initTRPC } from '@trpc/server';

// 1. Initialize tRPC
const t = initTRPC.create();

// 2. Create a router
const appRouter = t.router({
  // 3. Define a query named 'hello'
  hello: t.procedure.query(() => {
    return 'Hello from tRPC!';
  }),
});
// This snippet shows the core definition.
// A full server setup is needed to run it.

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