InstanceLinksHost

Kind: Class

Source: packages/core/injector/instance-links-host.ts

Part of: Core

InstanceLinksHost is Nest’s internal registry for locating provider instance links across the application’s modules. It indexes providers by injection token and returns the corresponding InstanceLink, which contains the resolved instance, wrapper metadata, and owning module context.

Methods

Where it refuses work

• InstanceLinksHost stops the work with UnknownElementException when !instanceLinksForGivenToken.
• InstanceLinksHost stops the work with UnknownElementException when !instanceLink.
• InstanceLinksHost stops the work with an early return when options.each.

Diagram

mermaid
graph LR
  Container[NestContainer] --> Modules[Registered Modules]
  Modules --> Providers[Provider Wrappers]
  Providers --> Links[InstanceLink entries]
  Links --> Host[InstanceLinksHost]
  Token[Injection Token] --> Host
  Host --> Result[InstanceLink / InstanceLink[]]

Usage

ts
import { InstanceLinksHost } from '@nestjs/core/injector/instance-links-host';
import { NestContainer } from '@nestjs/core/injector/container';
import { CatsService } from './cats.service';

// Nest normally creates and manages these internal objects.
const container = new NestContainer();
const instanceLinksHost = new InstanceLinksHost(container);

// Look up the provider link registered for a token.
const link = instanceLinksHost.get<CatsService>(CatsService);

// The link exposes the resolved provider instance and wrapper metadata.
const catsService = link.instance as CatsService;
catsService.findAll();

AI Coding Instructions

• Treat InstanceLinksHost as internal Nest injector infrastructure; prefer public APIs such as ModuleRef or app.get() in application code.
• Use the same injection token used during provider registration when calling get(), including class constructors, strings, symbols, or custom tokens.
• Handle missing tokens carefully: lookups for unregistered providers can throw an unknown-element error.
• Remember that a token may exist in multiple modules; use the appropriate lookup mode when integration code needs every matching InstanceLink.
• Do not mutate returned link metadata or provider wrappers, because they are shared by Nest’s dependency-injection container.