ContextIdResolver

Kind: Interface

Source: packages/core/helpers/context-id-factory.ts

Part of: Core

ContextIdResolver defines how Nest resolves a dependency-injection context ID for a given request or runtime payload. It pairs the original payload with a resolve function that selects the appropriate ContextId, enabling custom request-scoped and durable provider behavior.

Properties

Diagram

mermaid
graph LR
  A[Incoming Request / Payload] --> B[ContextIdStrategy.attach]
  B --> C[ContextIdResolver]
  C --> D[payload]
  C --> E[resolve HostComponentInfo]
  E --> F[ContextId]
  F --> G[Request-Scoped Provider Resolution]

Usage

ts
import {
  ContextIdFactory,
  ContextIdResolver,
  ContextIdStrategy,
  HostComponentInfo,
} from '@nestjs/core';

class CustomContextIdStrategy implements ContextIdStrategy {
  attach(contextId: object, request: unknown): ContextIdResolver {
    return {
      payload: request,
      resolve: (info: HostComponentInfo) => {
        // Reuse the same context for durable dependency trees.
        if (info.isTreeDurable) {
          return contextId;
        }

        // Create an isolated context for non-durable providers.
        return ContextIdFactory.create();
      },
    };
  }
}

ContextIdFactory.apply(new CustomContextIdStrategy());

AI Coding Instructions

• Return both the original request or runtime value through payload and a resolve function for selecting context IDs.
• Use resolve to distinguish durable provider trees from providers that require isolated request contexts.
• Ensure resolve always returns a valid ContextId, typically the supplied contextId or one created with ContextIdFactory.create().
• Register custom resolver behavior through a ContextIdStrategy and ContextIdFactory.apply(), rather than constructing resolvers in application code.
• Avoid storing mutable request-specific state in shared resolver instances; use the payload for per-request data.