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Version: 9.x

Inferring Types

It is often useful to wrap functionality of your @trpc/client or @trpc/react api within other functions. For this purpose, it's necessary to be able to infer input types, output types, and api paths generated by your @trpc/server router.

Inference Helpers

@trpc/server exports the following helper types to assist with inferring these types from the AppRouter exported by your @trpc/server router:

  • inferProcedureOutput<TProcedure>
  • inferProcedureInput<TProcedure>
  • inferSubscriptionOutput<TRouter, TPath>

Example Code

utils/trpc.ts
tsx
// trpc-helper.ts
import type { AppRouter } from 'api/src/routers/_app' // Import AppRouter from your main server router
import type { inferProcedureOutput, inferProcedureInput, inferSubscriptionOutput } from '@trpc/server'
/**
* Enum containing all api query paths
*/
export type TQuery = keyof AppRouter['_def']['queries']
/**
* Enum containing all api mutation paths
*/
export type TMutation = keyof AppRouter['_def']['mutations']
/**
* Enum containing all api subscription paths
*/
export type TSubscription = keyof AppRouter['_def']['subscriptions']
/**
* This is a helper method to infer the output of a query resolver
* @example type HelloOutput = InferQueryOutput<'hello'>
*/
export type InferQueryOutput<TRouteKey extends TQuery> = inferProcedureOutput<
AppRouter['_def']['queries'][TRouteKey]
>
/**
* This is a helper method to infer the input of a query resolver
* @example type HelloInput = InferQueryInput<'hello'>
*/
export type InferQueryInput<TRouteKey extends TQuery> = inferProcedureInput<
AppRouter['_def']['queries'][TRouteKey]
>
/**
* This is a helper method to infer the output of a mutation resolver
* @example type HelloOutput = InferMutationOutput<'hello'>
*/
export type InferMutationOutput<TRouteKey extends TMutation> =
inferProcedureOutput<AppRouter['_def']['mutations'][TRouteKey]>
/**
* This is a helper method to infer the input of a mutation resolver
* @example type HelloInput = InferMutationInput<'hello'>
*/
export type InferMutationInput<TRouteKey extends TMutation> =
inferProcedureInput<AppRouter['_def']['mutations'][TRouteKey]>
/**
* This is a helper method to infer the output of a subscription resolver
* @example type HelloOutput = InferSubscriptionOutput<'hello'>
*/
export type InferSubscriptionOutput<TRouteKey extends TSubscription> =
inferProcedureOutput<AppRouter['_def']['subscriptions'][TRouteKey]>
/**
* This is a helper method to infer the asynchronous output of a subscription resolver
* @example type HelloAsyncOutput = InferAsyncSubscriptionOutput<'hello'>
*/
export type InferAsyncSubscriptionOutput<TRouteKey extends TSubscription> =
inferSubscriptionOutput<AppRouter, TRouteKey>
/**
* This is a helper method to infer the input of a subscription resolver
* @example type HelloInput = InferSubscriptionInput<'hello'>
*/
export type InferSubscriptionInput<TRouteKey extends TSubscription> =
inferProcedureInput<AppRouter['_def']['subscriptions'][TRouteKey]>
utils/trpc.ts
tsx
// trpc-helper.ts
import type { AppRouter } from 'api/src/routers/_app' // Import AppRouter from your main server router
import type { inferProcedureOutput, inferProcedureInput, inferSubscriptionOutput } from '@trpc/server'
/**
* Enum containing all api query paths
*/
export type TQuery = keyof AppRouter['_def']['queries']
/**
* Enum containing all api mutation paths
*/
export type TMutation = keyof AppRouter['_def']['mutations']
/**
* Enum containing all api subscription paths
*/
export type TSubscription = keyof AppRouter['_def']['subscriptions']
/**
* This is a helper method to infer the output of a query resolver
* @example type HelloOutput = InferQueryOutput<'hello'>
*/
export type InferQueryOutput<TRouteKey extends TQuery> = inferProcedureOutput<
AppRouter['_def']['queries'][TRouteKey]
>
/**
* This is a helper method to infer the input of a query resolver
* @example type HelloInput = InferQueryInput<'hello'>
*/
export type InferQueryInput<TRouteKey extends TQuery> = inferProcedureInput<
AppRouter['_def']['queries'][TRouteKey]
>
/**
* This is a helper method to infer the output of a mutation resolver
* @example type HelloOutput = InferMutationOutput<'hello'>
*/
export type InferMutationOutput<TRouteKey extends TMutation> =
inferProcedureOutput<AppRouter['_def']['mutations'][TRouteKey]>
/**
* This is a helper method to infer the input of a mutation resolver
* @example type HelloInput = InferMutationInput<'hello'>
*/
export type InferMutationInput<TRouteKey extends TMutation> =
inferProcedureInput<AppRouter['_def']['mutations'][TRouteKey]>
/**
* This is a helper method to infer the output of a subscription resolver
* @example type HelloOutput = InferSubscriptionOutput<'hello'>
*/
export type InferSubscriptionOutput<TRouteKey extends TSubscription> =
inferProcedureOutput<AppRouter['_def']['subscriptions'][TRouteKey]>
/**
* This is a helper method to infer the asynchronous output of a subscription resolver
* @example type HelloAsyncOutput = InferAsyncSubscriptionOutput<'hello'>
*/
export type InferAsyncSubscriptionOutput<TRouteKey extends TSubscription> =
inferSubscriptionOutput<AppRouter, TRouteKey>
/**
* This is a helper method to infer the input of a subscription resolver
* @example type HelloInput = InferSubscriptionInput<'hello'>
*/
export type InferSubscriptionInput<TRouteKey extends TSubscription> =
inferProcedureInput<AppRouter['_def']['subscriptions'][TRouteKey]>