Hi there,

found some links in the KB that might help you:

Dynamic Cascading Drop-Down List 

Ajax Cascading Drop-Down List - includes a link to Joget Marketplace with a tutorial App

Hope this helps

When you select SelectBox 1 it populates Selectbox 2. Now based on those two selections Selectbox 3 is populated.

This is what I trying to do and it's not working.

I don't think its possible to have two field IDs to control the options of Selectbox 3 in the same form as Selectbox 1 & 2. I suggest to separate it into 2 Forms.

Here's what I did:

First, create the necessary tables for Form A,B,C. Next create a process with two activities. 

Map the 1st Activity with a form that contains selectbox 1 & 2 using Dynamic Cascading Drop-Down List method with each selectbox and assigned to a workflow variable each.

Then in the next activity, create a form that contains selectbox 3 and use the JDBC Binder to populate the options.

Here's an app as reference: APP_dynamicSelectbox-1-20191018110347.jwa

Hope this helps.