new

components.my-component.js

import Component from '@ember/component';
import EmberObject, { computed } from '@ember/object';
import { alias } from '@ember/object/computed';

export default Component.extend({
  dynamicModelProperty: computed('model', 'subpath', function() {
    let subpath = this.subpath;
    if (subpath) {
      let DynamicClass = EmberObject.extend({
        value: alias(`model.${subpath}`)
      });
      return DynamicClass.create({ model: this.model });
    }
    return EmberObject.create({});
  }),

  verbose: computed('dynamicModelProperty.value', function() {
    return (
      `watching ${this.subpath} with value: ${this.dynamicModelProperty.value} -- known model` +
      JSON.stringify(this.model)
    );
  })
});

controllers.application.js

import Controller from '@ember/controller';

export default Controller.extend({
  appName: 'Dynamic keys',
  
  animals: {
    chicken: {
      male: 20,
      female: 10
    },
    cow: {
      male: 200,
      female: 100,
    }
    pig: {
    	male: 10,
    	female: 30
  	}
  },

  actions: {
    incrementAnimal(type) {
      this.set(`animals.${type}.female`, this.get(`animals.${type}.female`) + 1);
      console.log('updated model', this.animals);
    }
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}

    <button onclick={{action 'incrementAnimal' 'cow'}}>+cow</button>
    <button onclick={{action 'incrementAnimal' 'chicken'}}>+chicken</button>
    <button onclick={{action 'incrementAnimal' 'pig'}}>+pig</button>

    {{my-component subpath='chicken' model=animals}}

    {{my-component subpath='cow' model=animals}}

    {{my-component subpath='pig' model=animals}}
    

<br>
<br>

templates.components.my-component.hbs

<h1>Watch {{subpath}}</h1>

<div>subpath: {{subpath}}</div>
<div>verbose: {{verbose}}</div>

twiddle.json

{
  "version": "0.15.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.4.3",
    "ember-template-compiler": "3.4.3",
    "ember-testing": "3.4.3"
  },
  "addons": {
    "ember-data": "3.4.2"
  }
}