Render Dropdown fields and bind Observables streams with Angular Formly

Your data model might have some property like nationId: 3. This number is usually a pointer to some other data model, those of the nations in this case. On the UI such fields are often represented as dropdown fields. In this lesson we're going to learn how to implement dropdown fields with Formly. We will also learn how Formly handles async data binding (such as the list of nations for the dropdown field) and how you can even directly bind RxJS Observables.