Version: 11.x

Define Procedures

A procedure is a function which is exposed to the client, it can be one of:

a Query - used to fetch data, generally does not change any data
a Mutation - used to send data, often for create/update/delete purposes
a Subscription - you might not need this, and we have dedicated documentation

Procedures in tRPC are very flexible primitives to create backend functions. They use an immutable builder pattern, which means you can create reusable base procedures that share functionality among multiple procedures.

Writing procedures

The t object you create during tRPC setup returns an initial t.procedure which all other procedures are built on:

ts
import { initTRPC } from '@trpc/server';
import { z } from 'zod';
 
const t = initTRPC.context<{ signGuestBook: () => Promise<void> }>().create();
 
export const router = t.router;
export const publicProcedure = t.procedure;
 
const appRouter = router({
  // Queries are the best place to fetch data
  hello: publicProcedure.query(() => {
    return {
      message: 'hello world',
    };
  }),
 
  // Mutations are the best place to do things like updating a database
  goodbye: publicProcedure.mutation(async (opts) => {
    await opts.ctx.signGuestBook();
 
    return {
      message: 'goodbye!',
    };
  }),
});

ts
import { initTRPC } from '@trpc/server';
import { z } from 'zod';
 
const t = initTRPC.context<{ signGuestBook: () => Promise<void> }>().create();
 
export const router = t.router;
export const publicProcedure = t.procedure;
 
const appRouter = router({
  // Queries are the best place to fetch data
  hello: publicProcedure.query(() => {
    return {
      message: 'hello world',
    };
  }),
 
  // Mutations are the best place to do things like updating a database
  goodbye: publicProcedure.mutation(async (opts) => {
    await opts.ctx.signGuestBook();
 
    return {
      message: 'goodbye!',
    };
  }),
});

Reusable "Base Procedures"

As a general pattern we recommend you rename and export t.procedure as publicProcedure, which then makes room for you to create other named procedures for specific use cases and export those too. This pattern is called "base procedures" and is a key pattern for code and behaviour re-use in tRPC; every application is likely to need it.

In the below code, we're using reusable base procedures to build common use-cases for our app - we're making a reusable base procedures for logged in users (authedProcedure) & another base procedure that takes an organizationId and validates that a user is part of that organization.

This is a simplified example; in practice you may want to use some combination of Headers, Context, Middleware, and Metadata, to authenticate and authorize your users.

ts
import { initTRPC, TRPCError } from '@trpc/server';
import { z } from 'zod';
 
type Organization = {
  id: string;
  name: string;
};
type Membership = {
  role: 'ADMIN' | 'MEMBER';
  Organization: Organization;
};
type User = {
  id: string;
  memberships: Membership[];
};
type Context = {
  /**
   * User is nullable
   */
  user: User | null;
};
 
const t = initTRPC.context<Context>().create();
 
export const publicProcedure = t.procedure;
 
// procedure that asserts that the user is logged in
export const authedProcedure = t.procedure.use(async function isAuthed(opts) {
  const { ctx } = opts;
  // `ctx.user` is nullable
  if (!ctx.user) {
            
(property) user: User | null
    throw new TRPCError({ code: 'UNAUTHORIZED' });
  }
 
  return opts.next({
    ctx: {
      // ✅ user value is known to be non-null now
      user: ctx.user,
    },
  });
});
 
// procedure that a user is a member of a specific organization
export const organizationProcedure = authedProcedure
  .input(z.object({ organizationId: z.string() }))
  .use(function isMemberOfOrganization(opts) {
    const membership = opts.ctx.user.memberships.find(
      (m) => m.Organization.id === opts.input.organizationId,
    );
    if (!membership) {
      throw new TRPCError({
        code: 'FORBIDDEN',
      });
    }
    return opts.next({
      ctx: {
        Organization: membership.Organization,
      },
    });
  });
 
export const appRouter = t.router({
  whoami: authedProcedure.mutation(async (opts) => {
    // user is non-nullable here
    const { ctx } = opts;
            const ctx: {
    user: User;
}
    return ctx.user;
  }),
  addMember: organizationProcedure
    .input(
      z.object({
        email: z.string().email(),
      }),
    )
    .mutation((opts) => {
      // ctx contains the non-nullable user & the organization being queried
      const { ctx } = opts;
              const ctx: {
    user: User;
    Organization: Organization;
}
 
      // input includes the validate email of the user being invited & the validated organizationId
      const { input } = opts;
               const input: {
    organizationId: string;
    email: string;
}
 
      return '...';
    }),
});

ts
import { initTRPC, TRPCError } from '@trpc/server';
import { z } from 'zod';
 
type Organization = {
  id: string;
  name: string;
};
type Membership = {
  role: 'ADMIN' | 'MEMBER';
  Organization: Organization;
};
type User = {
  id: string;
  memberships: Membership[];
};
type Context = {
  /**
   * User is nullable
   */
  user: User | null;
};
 
const t = initTRPC.context<Context>().create();
 
export const publicProcedure = t.procedure;
 
// procedure that asserts that the user is logged in
export const authedProcedure = t.procedure.use(async function isAuthed(opts) {
  const { ctx } = opts;
  // `ctx.user` is nullable
  if (!ctx.user) {
            
(property) user: User | null
    throw new TRPCError({ code: 'UNAUTHORIZED' });
  }
 
  return opts.next({
    ctx: {
      // ✅ user value is known to be non-null now
      user: ctx.user,
    },
  });
});
 
// procedure that a user is a member of a specific organization
export const organizationProcedure = authedProcedure
  .input(z.object({ organizationId: z.string() }))
  .use(function isMemberOfOrganization(opts) {
    const membership = opts.ctx.user.memberships.find(
      (m) => m.Organization.id === opts.input.organizationId,
    );
    if (!membership) {
      throw new TRPCError({
        code: 'FORBIDDEN',
      });
    }
    return opts.next({
      ctx: {
        Organization: membership.Organization,
      },
    });
  });
 
export const appRouter = t.router({
  whoami: authedProcedure.mutation(async (opts) => {
    // user is non-nullable here
    const { ctx } = opts;
            const ctx: {
    user: User;
}
    return ctx.user;
  }),
  addMember: organizationProcedure
    .input(
      z.object({
        email: z.string().email(),
      }),
    )
    .mutation((opts) => {
      // ctx contains the non-nullable user & the organization being queried
      const { ctx } = opts;
              const ctx: {
    user: User;
    Organization: Organization;
}
 
      // input includes the validate email of the user being invited & the validated organizationId
      const { input } = opts;
               const input: {
    organizationId: string;
    email: string;
}
 
      return '...';
    }),
});

Inferring the options type of a "Base Procedure"

In addition to being able to infer the input and output types of a procedure, you can also infer the options type of a specific procedure builder (or base procedure) using inferProcedureBuilderResolverOptions.

This type helper is useful for declaring a type to a function's parameters. Like for example, separating the procedure's handler (main execution code) from its definition at the router, or for creating a helper function that works with multiple procedures.

ts
async function getMembersOfOrganization(
  opts: inferProcedureBuilderResolverOptions<typeof organizationProcedure>,
) {
  // input and ctx are now correctly typed!
  const { ctx, input } = opts;
 
  return await prisma.user.findMany({
    where: {
      membership: {
        organizationId: ctx.Organization.id,
      },
    },
  });
}
export const appRouter = t.router({
  listMembers: organizationProcedure.query(async (opts) => {
    // use helper function!
    const members = await getMembersOfOrganization(opts);
 
    return members;
  }),
});

ts
async function getMembersOfOrganization(
  opts: inferProcedureBuilderResolverOptions<typeof organizationProcedure>,
) {
  // input and ctx are now correctly typed!
  const { ctx, input } = opts;
 
  return await prisma.user.findMany({
    where: {
      membership: {
        organizationId: ctx.Organization.id,
      },
    },
  });
}
export const appRouter = t.router({
  listMembers: organizationProcedure.query(async (opts) => {
    // use helper function!
    const members = await getMembersOfOrganization(opts);
 
    return members;
  }),
});

Subscriptions

For information on subscriptions, see our subscriptions guide.

Writing procedures​

Reusable "Base Procedures"​

Inferring the options type of a "Base Procedure"​

Subscriptions​

Writing procedures

Reusable "Base Procedures"

Inferring the options type of a "Base Procedure"

Subscriptions