Keep existing MRVS rows when dropdown changes and add new ones (no overwrite). Is dynamic column add

[skazeez0319]

I have a Record Producer with:

• A single-choice dropdown variable (let’s call it u_selector)
• A Multiple Row Variable Set (MRVS) (let’s call it u_items_mrvs) with a few columns (e.g., item, qty, comments)

What I’m doing now
Using a Catalog Client Script (onChange of u_selector), I populate the MRVS with multiple rows based on the selected value (e.g., selecting “ABC” adds 2–3 rows). This part is working.

My requirement

• When the user changes the dropdown to another option (e.g., from “ABC” to “XYZ”), the previous MRVS rows should remain, and the new selection’s rows should be added (not overwrite).
• Ideally:
  1. Add rows in the same MRVS, and mark which dropdown produced the rows, or
  2. Make another MRVS appear and collect rows there (all submitted in a single request).

Questions

1. Can MRVS add columns dynamically at runtime based on dropdown selection? If not, what’s the best pattern?
2. How can I merge/append rows into MRVS without wiping existing rows on each onChange?
3. Is it better to:
   • Use a single MRVS and tag rows with the source selection (e.g., a hidden source column), or
   • Use multiple MRVSs and show/hide them via UI Policies?
4. Server-side: What’s the cleanest way to consume MRVS JSON on Record Producer submission and map/store it?