Setting up Cascading Dropdowns between 2 dropdowns that are record lists

Question

I have a Matters dropdown and a Sub Matters dropdown that get their options from related tables. I want to make the choices in the Sub Matters dropdown dependent on the the selection in the Matters table. I know there needs to be a Query in the following expression section somewhere, however I am still trying to learn Appian and was hoping someone help me with the query and where to insert it..

Sanchit Gupta (Xebia) · Answer

In the local!SubMatterType, filter all the records having PSLM miscMatterSubType.miscMatterTypeId equal to local!selectedMatterType. 
 FYI,what you are trying to do at line 36 is not the correct way to save a value in a variable inside saveInto, instead use a!save(ri!variable, local!variable)

Harshit Bumb (Appyzie) · Answer

displayValue() should do the magic if you already have all the sub matters.
If not, you can select the Matter, pass that as a filter in subMatter's query and then use the output of the query to populate the choiceLabels and Values of subMatter dropdown!