Hey Maria,

For a long time, only one widget officially existed that made it possible to show the selected association in a dropdown, this widget was the Reference selector. 

Doc - https://docs.mendix.com/refguide/reference-selector/

A few months ago a widget called ComboBox was launched. This replaces most of the old widgets like the Reference selector, input reference set selector, Reference set selector and dropdown.  

It is available since version 9.24 and you can find more information through the official documentation:

Doc - https://docs.mendix.com/appstore/widgets/combobox/

Best Regards,

Ricardo Pereira

You can use a Reference Selector widget to do this. You just need to select which attribute in the associated object should be shown in the dropdown.

https://docs.mendix.com/refguide/reference-selector/

I hope this helps.

Reference Selector is nice and will do the trick, but since a couple of months, you can use the combobox, available here. Takes some getting-used-to, but once I got the hang of it I use it instead of the reference selector, reference set selector, input reference set selector and the dropdown, though not always. 

Read more about it here.

Good luck!