ember-changeset-validations custom relative validation

controllers.application.js

import Ember from 'ember';
import validateLessThan from '../validators/validateLessThanAttr';
export default Ember.Controller.extend({
  
  pairValidations: {
    smaller: validateLessThan('larger'),
  },
  
});

models.number-pair.js

import Model from "ember-data/model";
import attr from "ember-data/attr";

export default Model.extend({
  smaller: attr('number'),
  larger: attr('number'),
});

routes.application.js

import Ember from 'ember';

export default Ember.Route.extend({
  model() {
    return this.get('store').createRecord('numberPair', {
      smaller: 5,
      larger: 10,
    });  
  }
});

templates.application.hbs

<h1>Relative validation</h1>
<h2>Pick two numbers:</h2>
{{pick-two-numbers changeset=(changeset model pairValidations)}}

templates.components.pick-two-numbers.hbs

<label for="larger-num">Larger number ({{changeset.larger}}):</label>
<input
  type="number"
  id="larger-num"
  value={{changeset.larger}}
  oninput={{action (mut changeset.larger) value="target.value"}}
>
<br><br>
<label for="smaller-num">Smaller number ({{changeset.smaller}}):</label>
<input
  type="number"
  id="smaller-num"
  value={{changeset.smaller}}
  oninput={{action (mut changeset.smaller) value="target.value"}}
>
{{#each changeset.error.smaller.validation as |msg|}}
<p>{{msg}}</p>
{{/each}}

twiddle.json

{
  "version": "0.12.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.12.0",
    "ember-template-compiler": "2.12.0",
    "ember-testing": "2.12.0"
  },
  "addons": {
    "ember-data": "2.12.1",
    "ember-changeset-validations": "1.2.8"
  }
}

validators.validateLessThanAttr.js

export default function validateLessThanAttr(largerAttrName = '') {
  return (key, newValue, oldValue, changes, content) => {
    const largerValue = Ember.get(changes, largerAttrName) || Ember.get(content, largerAttrName);
    return parseInt(newValue) < parseInt(largerValue) || `Must be less than ${largerValue}`;
  }
}