ContextCreator

Kind: Class

Source: packages/core/helpers/context-creator.ts

Part of: Core

ContextCreator is a shared base class for building execution-context components from metadata attached to classes and methods. It collects global, class-level, and method-level metadata, then delegates to a concrete implementation to create the final context objects. It also provides consistent request-to-ContextId handling for request-scoped dependency resolution.

Methods

Diagram

mermaid
graph LR
  Request[Incoming request] --> ContextId[getContextId()]
  ContextId --> ContextFactory[ContextIdFactory]

  Controller[Controller / provider instance] --> CreateContext[createContext()]
  Handler[Handler callback] --> CreateContext
  MetadataKey[Metadata key] --> CreateContext

  Global[getGlobalMetadata()] --> CreateContext
  ClassMetadata[reflectClassMetadata()] --> CreateContext
  MethodMetadata[reflectMethodMetadata()] --> CreateContext

  CreateContext --> Concrete[createConcreteContext()]
  Concrete --> Result[Concrete context objects]

Usage

ts
import { ContextCreator } from '@nestjs/core/helpers/context-creator';
import { ContextIdFactory } from '@nestjs/core/helpers/context-id-factory';

const FEATURE_METADATA = 'feature:contexts';

class ExampleController {
  handleRequest() {
    return 'ok';
  }
}

// Obtain a concrete ContextCreator implementation from the framework or adapter.
declare const contextCreator: ContextCreator;

const controller = new ExampleController();
const request = { headers: { 'x-request-id': 'req-123' } };

// Reuse the same ContextId when resolving request-scoped dependencies.
const contextId = contextCreator.getContextId(request, false);

const contexts = contextCreator.createContext(
  controller,
  controller.handleRequest,
  FEATURE_METADATA,
  contextId,
);

console.log(contexts);

AI Coding Instructions

• Treat ContextCreator as infrastructure: use a concrete context creator implementation rather than duplicating metadata collection logic.
• Preserve metadata precedence when extending behavior: global metadata is combined with class metadata and then method metadata.
• Pass the same ContextId through the execution flow so request-scoped providers resolve consistently.
• Use stable metadata keys for decorators and ensure metadata is applied to the intended class or handler function.
• Keep createConcreteContext() focused on converting merged metadata into runtime context objects; avoid performing reflection there.

Relationships

• IMPORTS → Controller