CODEWITHSUNDEEP
typescripttypescript2.0tsc
Alexander Mills
Alexander Mills

Reputation: 99970

Use generics to declare type of return value of class method

I have the following:

export class RootCtrl {

  m: Model<any>;

  constructor(m: Model<any>) {
    this.m = m;
  }

  doFindMany(query: object, options?: CDTModelOpts, cb?: MongoErrorCB){

    const Model = this.m;

    // cb is optional, if cb == null, returns promise
    const {populate, lean} = options || ({} as CDTModelOpts);

    let q = Model.find(query);

    if (populate && populate.length > 0) {
      q = q.populate(populate);
    }

    if (lean !== false) {
      q = q.lean();
    }

    return q.lean().exec(cb)
  }

}

what I want to do, is declare a return type for this wrapper method...something like this:

  doFindMany(query: object, options?: CDTModelOpts, cb?: MongoErrorCB) : Array<typeof this.m> {

    const Model = this.m;

    // cb is optional, if cb == null, returns promise
    const {populate, lean} = options || ({} as CDTModelOpts);

    let q = Model.find(query);

    if (populate && populate.length > 0) {
      q = q.populate(populate);
    }

    if (lean !== false) {
      q = q.lean();
    }

    return q.lean().exec(cb)
  }

the return type, is the type of the Model value that gets passed in. The syntax I use is totally bogus however. Is there a way for the return type to reflect the typeof an input parameter to the constructor?

Upvotes: 0

Views: 70

Answers (1)

Vayrex
Vayrex

Reputation: 1467

Seems you need something like here.

  export class RootCtrl<ModelType> {

  m: Model<ModelType>;

  constructor(m: Model<ModelType>) {
    this.m = m;
  }

  doFindMany(query: object, options?: CDTModelOpts, cb?: MongoErrorCB): Array<Model<ModelType>>{

    const Model = this.m;

    // cb is optional, if cb == null, returns promise
    const {populate, lean} = options || ({} as CDTModelOpts);

    let q = Model.find(query);

    if (populate && populate.length > 0) {
      q = q.populate(populate);
    }

    if (lean !== false) {
      q = q.lean();
    }

    return q.lean().exec(cb)
  }

}

Upvotes: 1

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