ember-drag-sort updating attribute on parent, approach 2

components.the-item.js

import Ember from 'ember';

export default Ember.Component.extend({
  classNames: ['the-item'],
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  actions : {
    dragEnd ({sourceList, sourceIndex, targetList, targetIndex}) {
      if (sourceList === targetList && sourceIndex === targetIndex) return

      const draggedItem = sourceList.objectAt(sourceIndex)
      const oldParent = draggedItem.get('parent')                     // <--

      sourceList.removeAt(sourceIndex)
      targetList.insertAt(targetIndex, draggedItem)
      
      const newParent = draggedItem.get('parent')                     // <--
      
      newParent.set('isParent', newParent.get('children.length') > 0) // <--
      oldParent.set('isParent', oldParent.get('children.length') > 0) // <--
    },
  }
  
});

models.item.js

import Model from "ember-data/model";
import attr from "ember-data/attr";
import { belongsTo, hasMany } from "ember-data/relationships";

export default Model.extend({
  isParent: attr('boolean'),
  
  parent: belongsTo('item', {inverse: 'children', async: false}),
  children: hasMany('item', {inverse: 'parent',   async: false}),
  
  // updateParentState: Ember.observer('children.[]', function () {
  //  const isParent = this.get('children.length') > 0
  //   this.setProperties({isParent})
  // })
});

routes.application.js

import Ember from 'ember';

const payload = {
  data: [
    {
      type: 'item',
      id: '0',
      attributes: { isParent: true },
      relationships: {
        parent: { data: { type: 'item', id: '0' } },
        children: {
          data: [
            {type: 'item', id: '1'},
            {type: 'item', id: '4'},
          ]
        }
      }
    },
    {
      type: 'item',
      id: '1',
      attributes: { isParent: true },
      relationships: {
        parent: { data: { type: 'item', id: '0' } },
        children: {
          data: [
            {type: 'item', id: '2'},
            {type: 'item', id: '3'},
          ]
        }
      }
    },
    {
      type: 'item',
      id: '2',
      attributes: { isParent: false },
      relationships: {
        parent: { data: { type: 'item', id: '1' } },
        children: {
          data: []
        }
      }
    },
    {
      type: 'item',
      id: '3',
      attributes: { isParent: false },
      relationships: {
        parent: { data: { type: 'item', id: '1' } },
        children: {
          data: []
        }
      }
    },
    {
      type: 'item',
      id: '4',
      attributes: { isParent: true },
      relationships: {        parent: { data: { type: 'item', id: '0' } },
        children: {
          data: [
            {type: 'item', id: '5'},
            {type: 'item', id: '6'},
          ]
        }
      }
    },
    {
      type: 'item',
      id: '5',
      attributes: { isParent: false },
      relationships: {
        parent: { data: { type: 'item', id: '4' } },
        children: {
          data: []
        }
      }
    },
    {
      type: 'item',
      id: '6',
      attributes: { isParent: false },
      relationships: {
        parent: { data: { type: 'item', id: '4' } },
        children: {
          data: []
        }
      }
    },
  ]
}

export default Ember.Route.extend({
  
  model () {
    const store = this.get('store')
    
    store.push(payload)
    
    return store.peekRecord('item', '0')
  }
});

styles.app.css

body {
  margin: 12px 16px;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 12pt;
}

.the-item {
  margin: 4px;
  padding: 1em;
  border: 1px solid black;
  display: flex;
}

.the-item-title {
  flex-shrink: 0;
  flex-grow: 0;
  width: 100px;
}

.the-item .dragSortList {
  flex-shrink: 0;
  flex-grow: 1;
}

.the-item .dragSortList.-isExpanded {
  padding-top: 55px;
}

.the-item .dragSortList.-isDragging {
  outline: 2px dashed black;
  background-color: deepskyblue;
}

.the-item .dragSortList.-isExpanded.-isDraggingOver:before {
  top: 15px;
}

.the-item {
  background-color : #FFD0E9;
}
.the-item .the-item {
  background-color: #FFAAD7;
}

.the-item .the-item .the-item {
  background-color: #FF8CC9;
}
.the-item .the-item .the-item .the-item {
  background-color: #FF74BD;
}
.the-item .the-item .the-item .the-item .the-item {
  background-color: #FF60B4;
}
.the-item .the-item .the-item .the-item .the-item .the-item {
  background-color: #FF50AD;
}

templates.application.hbs

{{the-item
  item = model
  dragEndAction = (action 'dragEnd')
}}

templates.components.the-item.hbs

<p class = "the-item-title">
  {{item.id}} {{item.isParent}}
</p>

{{#drag-sort-list
  items               = item.children
  group               = group
  dragEndAction       = dragEndAction
  as |child|
}}
  {{the-item
    item          = child
    group         = group
    dragEndAction = dragEndAction
  }}
{{/drag-sort-list}}

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-drag-sort": "1.0.2"
  }
}