TopologyTree

Kind: Class

Source: packages/core/injector/topology-tree/topology-tree.ts

Part of: Core

TopologyTree represents the hierarchical import topology of modules during dependency-injection container setup. Its walk() method traverses the tree from the root module, allowing internal tooling to inspect each module and its depth in the topology.

Methods

Where it refuses work

• TopologyTree stops the work with an early return when !node.value.imports.
• TopologyTree stops the work with an early return when !child.
• TopologyTree stops the work with an early return when node.hasCycleWith(child).

Diagram

mermaid
graph LR
  Root[Root Module] --> FeatureA[Feature Module A]
  Root --> FeatureB[Feature Module B]
  FeatureA --> Shared[Shared Module]

  Walk[TopologyTree.walk()] --> Root
  Walk --> Callback["callback(module, depth)"]

Usage

ts
import { TopologyTree } from '@nestjs/core/injector/topology-tree/topology-tree';

// `rootModule` is the root Module instance created by the container.
const topologyTree = new TopologyTree(rootModule);

// Traverse modules in the topology and use their nesting depth.
topologyTree.walk((moduleRef, depth) => {
  if (!moduleRef.isGlobal) {
    moduleRef.distance = depth;
  }

  console.log(`${'  '.repeat(depth)}${moduleRef.metatype?.name}`);
});

AI Coding Instructions

• Use walk() for read-only traversal tasks such as calculating module distance, collecting metadata, or inspecting module relationships.
• Treat TopologyTree as an internal injector/container utility; avoid depending on it from application-level modules.
• Preserve the callback’s depth value when adding traversal-based logic, since it represents the module’s position relative to the root.
• Do not mutate the module import graph while walking it; build the topology first, then traverse it.

How it works

TopologyTree

TopologyTree is a private-structure builder for a graph of Module instances connected through each module’s imports set. It stores one TreeNode<Module> per encountered module in a Map, rooted at the Module passed to its constructor. topology-tree.ts:4-6