dag-maker

DAG Maker

DAG maker utilize topological sorting to make directed acyclic graphs.

It can be used to solve following problems:

• Dependency resolution & injection
• Figure out services start & stop order
• Create & destroy objects in reasonable order

Installation

npm i dag-maker

Usage

Suppose we have two classes A and B. The dependency graph as follows:

A <- B

To instantiate them, first we create an instance of A, then pass the instance to B's constructor. Since there are only two classes, it's quite straightforward.

However, when it comes to a dozen classes with complex dependencies, it's no longer feasible to figure out the proper construction order manually. Not to mention the destruction order.

Here is an example (in TypeScript) presents how to solve this kind of problem with dag-maker:

import { dependencies, DagMaker } from 'dag-maker';

class A {
  static async create() {
    console.log('create A');
    return new A();
  }
  static async destroy(a: A) {
    console.log('destroy A:', a);
  }
}

@dependencies({
  a: A,
})
class B {
  constructor(a: A) {
    this.a = a;
  }
  static async create(options: { a: A }) {
    console.log('create B');
    return new B(options.a);
  }
  static async destroy(b: B) {
    console.log('destroy B:', b);
  }
}

const dagMaker = new DagMaker(A, B);
console.log(dagMaker.orderBy('dependencies'));
// [ [ 'A' ], [ 'B' ] ]

console.log(dagMaker.orderBy('dependents'));
// [ [ 'B' ], [ 'A' ] ]

const dag = await dagMaker.create();
// create A
// create B

console.log(dag);
// Map(2) { 'A' => A {}, 'B' => B { a: A {} } }

await dagMaker.destroy(dag);
// destroy B: B { a: A {} }
// destroy A: A {}

In this example, we implement factory methods create() and destroy() right inside class A and B, and declare B's dependencies with a decorator @dependencies. If you don't want to use decorator, declare a static variable named dependencies could achieve the same semantic. After then, we create a DagMaker for class A and B. Eventually, the DAG maker will inspect dependencies property and figure out how to construct A and B.