title: MobX observable with dynamic data
body: <p>I have the following class</p>
  
  <pre><code>export default class BaseStore {
    @observable model ;
  
    @action updateStore(propertyName, newValue) {
      this.model[propertyName] = newValue;
    }
  }
  </code></pre>
  
  <p>In child classes I add layers to the observable model, such as :</p>
  
  <pre><code>model.payment.type = 'credit card'
  </code></pre>
  
  <p>My react component doesn't render automatically when this happen, it does however, if I has a top level data such as:</p>
  
  <pre><code>model.Type = 'CreditCard'
  </code></pre>
  
  <p>I am new to MobX, and read that I need to make use of map() but I am unable to find a decent example that explain how to use it.</p>