Server Side Calls

You may need to call your procedure(s) directly from the server, createCaller() function returns you an instance of RouterCaller able to execute queries and mutations.

info

createCaller should not be used to call procedures from within other procedures. This creates overhead since you'll need to (potentially) create context again, run through all the middlewares and validate the input with the input parsers - all of these which have already been done when the procedure was initially called. Instead, you should extract the shared logic into a separate function and call that from within the procedures.

Create caller

With the router.createCaller({}) function (first argument is Context) we retrieve an instance of RouterCaller.

Input query example

We create the router with an input query, and then we call the asynchronous greeting procedure to get the result.

ts
import { initTRPC } from '@trpc/server';
import { z } from 'zod';
 
const t = initTRPC.create();
 
const router = t.router({
  // Create procedure at path 'greeting'
  greeting: t.procedure
    .input(z.object({ name: z.string() }))
    .query(({ input }) => `Hello ${input.name}`),
});
 
const caller = router.createCaller({});
const result = await caller.greeting({ name: 'tRPC' });
        
const result: string

ts
import { initTRPC } from '@trpc/server';
import { z } from 'zod';
 
const t = initTRPC.create();
 
const router = t.router({
  // Create procedure at path 'greeting'
  greeting: t.procedure
    .input(z.object({ name: z.string() }))
    .query(({ input }) => `Hello ${input.name}`),
});
 
const caller = router.createCaller({});
const result = await caller.greeting({ name: 'tRPC' });
        
const result: string

Mutation example

We create the router with a mutation, and then we call the asynchronous post procedure to get the result.

ts
import { initTRPC } from '@trpc/server';
import { z } from 'zod';
 
const posts = ['One', 'Two', 'Three'];
 
const t = initTRPC.create();
const router = t.router({
  post: t.router({
    add: t.procedure.input(z.string()).mutation(({ input }) => {
      posts.push(input);
      return posts;
    }),
  }),
});
 
const caller = router.createCaller({});
const result = await caller.post.add('Four');
        
const result: string[]

ts
import { initTRPC } from '@trpc/server';
import { z } from 'zod';
 
const posts = ['One', 'Two', 'Three'];
 
const t = initTRPC.create();
const router = t.router({
  post: t.router({
    add: t.procedure.input(z.string()).mutation(({ input }) => {
      posts.push(input);
      return posts;
    }),
  }),
});
 
const caller = router.createCaller({});
const result = await caller.post.add('Four');
        
const result: string[]

Context with middleware example

We create a middleware to check the context before executing the secret procedure. Below are two examples: the former fails because the context doesn't fit the middleware logic, and the latter works correctly.

info

Middlewares are performed before any procedure(s) are called.

ts
import { TRPCError, initTRPC } from '@trpc/server';
 
type Context = {
  user?: {
    id: string;
  };
};
const t = initTRPC.context<Context>().create();
 
const isAuthed = t.middleware(({ next, ctx }) => {
  if (!ctx.user) {
    throw new TRPCError({
      code: 'UNAUTHORIZED',
      message: 'You are not authorized',
    });
  }
 
  return next({
    ctx: {
      // Infers that the `user` is non-nullable
      user: ctx.user,
    },
  });
});
 
const protectedProcedure = t.procedure.use(isAuthed);
 
const router = t.router({
  secret: protectedProcedure.query(({ ctx }) => ctx.user),
});
 
{
  // ❌ this will return an error because there isn't the right context param
  const caller = router.createCaller({});
 
  const result = await caller.secret();
}
 
{
  // ✅ this will work because user property is present inside context param
  const authorizedCaller = router.createCaller({
    user: {
      id: 'KATT',
    },
  });
  const result = await authorizedCaller.secret();
          
const result: {
    id: string;
}
}

ts
import { TRPCError, initTRPC } from '@trpc/server';
 
type Context = {
  user?: {
    id: string;
  };
};
const t = initTRPC.context<Context>().create();
 
const isAuthed = t.middleware(({ next, ctx }) => {
  if (!ctx.user) {
    throw new TRPCError({
      code: 'UNAUTHORIZED',
      message: 'You are not authorized',
    });
  }
 
  return next({
    ctx: {
      // Infers that the `user` is non-nullable
      user: ctx.user,
    },
  });
});
 
const protectedProcedure = t.procedure.use(isAuthed);
 
const router = t.router({
  secret: protectedProcedure.query(({ ctx }) => ctx.user),
});
 
{
  // ❌ this will return an error because there isn't the right context param
  const caller = router.createCaller({});
 
  const result = await caller.secret();
}
 
{
  // ✅ this will work because user property is present inside context param
  const authorizedCaller = router.createCaller({
    user: {
      id: 'KATT',
    },
  });
  const result = await authorizedCaller.secret();
          
const result: {
    id: string;
}
}

Example for a Next.js API endpoint

tip

This example shows how to use the caller in a Next.js API endpoint. tRPC creates API endpoints for you already, so this file is only meant to show how to call a procedure from another, custom endpoint.

ts
import { TRPCError } from '@trpc/server';
import { getHTTPStatusCodeFromError } from '@trpc/server/http';
import type { NextApiRequest, NextApiResponse } from 'next';
import { appRouter } from '~/server/routers/_app';
 
type ResponseData = {
  data?: {
    postTitle: string;
  };
  error?: {
    message: string;
  };
};
 
export default async (
  req: NextApiRequest,
  res: NextApiResponse<ResponseData>,
) => {
  /** We want to simulate an error, so we pick a post ID that does not exist in the database. */
  const postId = `this-id-does-not-exist-${Math.random()}`;
 
  const caller = appRouter.createCaller({});
 
  try {
    // the server-side call
    const postResult = await caller.post.byId({ id: postId });
 
    res.status(200).json({ data: { postTitle: postResult.title } });
  } catch (cause) {
    // If this a tRPC error, we can extract additional information.
    if (cause instanceof TRPCError) {
      // We can get the specific HTTP status code coming from tRPC (e.g. 404 for `NOT_FOUND`).
      const httpStatusCode = getHTTPStatusCodeFromError(cause);
 
      res.status(httpStatusCode).json({ error: { message: cause.message } });
      return;
    }
 
    // This is not a tRPC error, so we don't have specific information.
    res.status(500).json({
      error: { message: `Error while accessing post with ID ${postId}` },
    });
  }
};

ts
import { TRPCError } from '@trpc/server';
import { getHTTPStatusCodeFromError } from '@trpc/server/http';
import type { NextApiRequest, NextApiResponse } from 'next';
import { appRouter } from '~/server/routers/_app';
 
type ResponseData = {
  data?: {
    postTitle: string;
  };
  error?: {
    message: string;
  };
};
 
export default async (
  req: NextApiRequest,
  res: NextApiResponse<ResponseData>,
) => {
  /** We want to simulate an error, so we pick a post ID that does not exist in the database. */
  const postId = `this-id-does-not-exist-${Math.random()}`;
 
  const caller = appRouter.createCaller({});
 
  try {
    // the server-side call
    const postResult = await caller.post.byId({ id: postId });
 
    res.status(200).json({ data: { postTitle: postResult.title } });
  } catch (cause) {
    // If this a tRPC error, we can extract additional information.
    if (cause instanceof TRPCError) {
      // We can get the specific HTTP status code coming from tRPC (e.g. 404 for `NOT_FOUND`).
      const httpStatusCode = getHTTPStatusCodeFromError(cause);
 
      res.status(httpStatusCode).json({ error: { message: cause.message } });
      return;
    }
 
    // This is not a tRPC error, so we don't have specific information.
    res.status(500).json({
      error: { message: `Error while accessing post with ID ${postId}` },
    });
  }
};