How to get related records without using Apex?

getRelatedListRecords

You can utilize this wire adapter to access RelatedList records. Related lists present information and links to records linked with a particular record. For instance, an account might have related lists for contacts, cases, notes, or files.

Demo Code:

import { LightningElement, wire, api } from 'lwc';

import { getRelatedListRecords } from 'lightning/uiRelatedListApi';

export default class Acc extends LightningElement {

    error;

  records;

     @wire(getRelatedListRecords, {

    parentRecordId: '0015g00000DMcjgAAD',

    relatedListId: 'Contacts',

    fields: ['Contact.Name','Contact.Id'],

    sortBy: ['Contact.Name']

  })

  listInfo({ error, data }) {

    if (data) {

      this.records = data.records;

      console.log('test Dataa ', this.records);

      this.error = undefined;

    } else if (error) {

      this.error = error;

      this.records = undefined;

    }

  }

}

Parameters 

• parentRecordId—(Required) The ID of the parent record that you want to get related lists for, like an Account ID.
• relatedListId—(Required) The API name of a related list object, like Contacts, Opportunities, or Cases.
• fields—(Optional) The API names of the related list’s column fields.
• optionalFields—(Optional) The API names of additional fields in the related list.
• pageSize—(Optional) The number of list records to return per page.
• sortBy—(Optional) An array of field API names to sort the related list by. Accepts only one value per request.
• where—(Optional) The filter to apply to related list records.

Demo: