Filter child field options by a parent field There are many scenes, each assigned by an entity reference field to exactly one show. Same for set pieces.

Show
&mdash;Scene
&mdash;Set piece

I am using entity references rather than taxonomy so that non-technical users can add shows, scenes and set pieces easily.  And when users add content, they select a reference to show it belongs to, and optionally a particular scene and optionally a particular set piece.

When they select the show on the first field, how can I have scene and set piece fields under it only show the scene and set piece options for that show?
I have done this type of thing before. I did it by creating a map (array) of what 'scenes' belong to which 'shows' and sent the javascript array to the page with a hook_form_alter. I then used javascript/jquery to listen for the change event on the 'show' dropdown which then hid or displayed the the corresponding 'scenes' using the array as reference. It could also be done via ajax if you preferred.