Developing Mutation Procedures
Build procedures for data creation, update, and deletion operations using tRPC mutation procedures.
Developing Mutation Procedures 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.
What Are tRPC Mutations?
Welcome to tRPC mutation procedures! So far, you've likely used queries to fetch data, like getting a list of users or a single product.
But what if you need to change data? This is where mutations come in. Mutations are API operations designed to modify data on your server.
- Create: Add new records (e.g., create a user).
- Update: Modify existing records (e.g., update a user's email).
- Delete: Remove records (e.g., delete a user).
They are the 'CUD' in CRUD operations!
Mutations vs. Queries
It's important to understand the difference between queries and mutations in tRPC:
- Queries: Used for fetching data. They are typically read-only and should not have side effects (i.e., they don't change data on the server).
- Mutations: Used for changing data. They are designed to have side effects and modify your server's state.
tRPC enforces this separation, helping you build more predictable and robust APIs. When you need to create, update, or delete anything, always reach for a mutation.
Defining a Simple Mutation
Let's start by defining a very simple mutation. Just like queries, mutations are procedures within your tRPC router.
We use .mutation() instead of .query(). This example takes a name as input and returns a greeting string.
import { initTRPC } from '@trpc/server';
import { z } from 'zod';
const t = initTRPC.create();
const appRouter = t.router({
sayHello: t.procedure
.input(z.object({ name: z.string() }))
.mutation(({ input }) => {
// In a real app, this might save 'name' to a log
return `Hello, ${input.name}!`;
}),
});
export type AppRouter = typeof appRouter;
// This defines a valid tRPC router with one mutation.Creating Data: The 'Create' Mutation
A common use case for mutations is creating new data. Let's build a createUser mutation that accepts a user's name and email.
We'll use zod (a schema validation library) to define the expected input structure. This ensures type safety and validates incoming data automatically.
import { initTRPC } from '@trpc/server';
import { z } from 'zod';
const t = initTRPC.create();
interface User {
id: string;
name: string;
email: string;
}
const users: User[] = []; // Our 'database'
const appRouter = t.router({
createUser: t.procedure
.input(z.object({
name: z.string().min(1),
email: z.string().email(),
}))
.mutation(({ input }) => {
const newUser: User = {
id: `user-${users.length + 1}`,
name: input.name,
email: input.email,
};
users.push(newUser); // Add to our fake database
return newUser; // Return the new user object
}),
});
export type AppRouter = typeof appRouter;
// This router defines how to create a user.Updating Data: The 'Update' Mutation
Next, let's tackle updating existing data. An updateUser mutation will need the id of the user to update, plus the fields that need changing.
Notice how we can make fields .optional() in our Zod schema if they might not always be provided during an update.
import { initTRPC } from '@trpc/server';
import { z } from 'zod';
const t = initTRPC.create();
interface User {
id: string;
name: string;
email: string;
}
const users: User[] = [
{ id: 'user-1', name: 'Alice', email: 'alice@example.com' },
];
const appRouter = t.router({
updateUser: t.procedure
.input(z.object({
id: z.string(),
name: z.string().min(1).optional(),
email: z.string().email().optional(),
}))
.mutation(({ input }) => {
const userIndex = users.findIndex(u => u.id === input.id);
if (userIndex === -1) {
throw new Error('User not found');
}
// Merge existing data with new input
users[userIndex] = { ...users[userIndex], ...input };
return users[userIndex]; // Return the updated user
}),
});
export type AppRouter = typeof appRouter;
// This router defines how to update a user.Deleting Data: The 'Delete' Mutation
Finally, let's create a mutation to delete data. A deleteUser mutation typically only needs the id of the record to remove.
For the return value, you might send back a simple success message or the ID of the deleted item. Here, we'll return a boolean indicating success.
import { initTRPC } from '@trpc/server';
import { z } from 'zod';
const t = initTRPC.create();
interface User {
id: string;
name: string;
email: string;
}
const users: User[] = [
{ id: 'user-1', name: 'Alice', email: 'alice@example.com' },
{ id: 'user-2', name: 'Bob', email: 'bob@example.com' },
];
const appRouter = t.router({
deleteUser: t.procedure
.input(z.object({ id: z.string() }))
.mutation(({ input }) => {
const initialLength = users.length;
const userIndex = users.findIndex(u => u.id === input.id);
if (userIndex !== -1) {
users.splice(userIndex, 1); // Remove from array
}
// Return true if an item was removed
return { success: users.length < initialLength };
}),
});
export type AppRouter = typeof appRouter;
// This router defines how to delete a user.Client-Side Mutation Calls
Now that you've defined your mutations on the server, how do you call them from your frontend application?
Using the tRPC client, you simply access the mutation by its name and call the .mutate() method, passing your input data.
import { createTRPCProxyClient, httpBatchLink } from '@trpc/client';
// A simplified AppRouter type for this client-side example.
// In a real app, you'd import 'AppRouter' from your shared types.
interface User { id: string; name: string; email: string; }
type AppRouter = {
sayHello: (input: { name: string }) => Promise<string>;
createUser: (input: { name: string; email: string }) => Promise<User>;
deleteUser: (input: { id: string }) => Promise<{ success: boolean }>;
};
const trpc = createTRPCProxyClient<AppRouter>({
links: [
httpBatchLink({
url: 'http://localhost:3000/trpc', // Your tRPC server URL
}),
],
});
async function runMutationCalls() {
console.log('1. Calling sayHello...');
const helloRes = await trpc.sayHello.mutate({ name: 'Coddy' });
console.log(`Result: ${helloRes}`);
console.log('2. Calling createUser...');
const newUser = await trpc.createUser.mutate({
name: 'Eve',
email: 'eve@example.com',
});
console.log('Created:', newUser);
console.log('3. Calling deleteUser...');
const deleteRes = await trpc.deleteUser.mutate({ id: newUser.id });
console.log('Deleted:', deleteRes.success);
}
runMutationCalls();
// This script simulates client-side mutation calls.Handling Results and Errors
When you call a mutation from the client, it returns a Promise. You can use await to wait for the result, just like with any asynchronous operation.
For error handling, you can use standard JavaScript try...catch blocks around your .mutate() calls. tRPC will automatically propagate errors from your backend to the client.
try {
const result = await trpc.createUser.mutate({ ... });
// Handle success
} catch (error) {
// Handle error
console.error('Mutation failed:', error.message);
}This makes error management straightforward and type-safe.
When to Use Mutations
Remember to use mutations for any operation that changes data on your server. This includes:
- Submitting a form (e.g., user registration, posting a comment).
- Toggling a setting (e.g., dark mode preference).
- Performing administrative actions (e.g., banning a user).
- Uploading files (though this can involve special handling).
By consistently using mutations for these actions, you maintain clarity, type safety, and leverage tRPC's powerful features for data modification.
Check Your Mutation Knowledge
You've learned how to define and use tRPC mutation procedures. Time for a quick check!
Recap: Mutation Procedures
Great job! In this lesson, you've mastered tRPC mutation procedures:
- You learned that mutations are for operations that change data (Create, Update, Delete).
- You saw how to define mutations using
t.procedure.mutation()with input validation via Zod. - You built examples for creating, updating, and deleting data on the server.
- You understood how to call these mutations from the client and handle their results.
Mutations are a core part of building interactive and data-driven applications with tRPC. Next, we'll explore input validation more deeply with Zod!
Frequently asked questions
Is the “Developing Mutation Procedures” lesson free?
Yes — the full text of “Developing Mutation Procedures” 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 “Developing Mutation Procedures”?
Build procedures for data creation, update, and deletion operations using tRPC mutation procedures. 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 “Developing Mutation Procedures” 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
- Structuring with tRPC Routers
- Implementing Query Procedures
- Developing Mutation Procedures
- Merging and Nesting Routers