Conditional options in nested form

[lucasferreira]

I have relational schema with some tables. Something like that:

The packages are linked to the samples, whitch are linked to the projects, whitch have a category.
But there's a business rule: only certain packages are avaliable for each category.

That said, In the nested form how can I filter the options that will appear in the "Package" option of my form based in the data that are in the table "Categories", that are three levels up?

this is the inicial page, the user may select the category and the project and click in "new" to add the samples

when adding the samples, the usar may select the package

currently all package options appear, but I neet to show only the avaliable options. 

 
I dont know to do that, I think the correct answer is to use a "valid if" expression, by dont know which expression and in which column it should be set.

[Marc_Dillon · Accepted solution]

Yes, using valid_if is correct!

https://help.appsheet.com/en/articles/961544-dropdown-from-valid_if

https://help.appsheet.com/en/articles/961554-dependent-dropdown

[lucasferreira]

Okay, I know that, but in that case, where do it set the valid if expression?