Mixins in loopback4

Question

I want to add createdAt and updatedAt to each model on loopback 4

can not find name 'MixinTarget'.

Type parameter 'T' of exported function has or is using private name 'MixinTarget'.

If I try from documentation above error occurs.

Answer 1

MixinTaget must be imported from @loopback/core:

import {MixinTarget} from '@loopback/core';
import {Class} from '@loopback/repository';

export function TimeStampMixin<T extends MixinTarget<object>>(baseClass: T) {
  return class extends baseClass {
    // add a new property `createdAt`
    // eslint-disable-next-line @typescript-eslint/ban-ts-comment
    // @ts-ignore
    public createdAt: Date;
    constructor(...args: any[]) {
      super(args);
      this.createdAt = new Date();
    }
    printTimeStamp() {
      console.log('Instance created at: ' + this.createdAt);
    }
  };
}

Further reading

As of the writing of this answer, the docs hasn't been updated to reflect the latest clarifications.

• https://github.com/strongloop/loopback-next/blob/4932c6c60c25df885b4166b7c4c425eba457a73b/docs/site/Mixin.md

Answer 2

To resolve this issue, I didn't use the mixin approach. I added the following fields to my model.

  @property({
    type: 'date',
    default: () => new Date(),
    postgresql: {
      columnName: 'updated_at',
    },
  })
  updatedAt?: Date;

It should work as expected