Adding values to a multi-select field with deluge

Because subforms will only create new rows, I'm using deluge to recall information from a form into the subrows to mimic the behaviour of updating a row rather than creating it.

I have a multi select field called "locations" that is a list of locations for the client, and for every one they choose the subrow is populated with the existing data about that location from a form called "location" (confusing I know). When the form is saved it pushes any updates to that original form and all is well.

When the client edits the form I need a way to rebuild that subform data and the choices in the multi select. However I'm having trouble pushing the results to the multiselect field.

I hope this helps :

// Get all the choices that were made for this record
varFetchChoices = benchmarks [ ID == input.ID ].locations.getAll();
//Clear existing subrows and choices
clear locations;
input.SUB_LOCATIONS.clear();
//Rebuild the multiselect by looking up each location
varFetch =benchmarks [ ID == input.ID ].locations.getAll();
for each varRow in varFetch
{
input.locations = varRow;
}

When I set up an alert on varRow, it displays the ID of each of the locations separately as I would expect, but it only ever inputs the one location.

I suspect it's because I need to add the varRow to a list and then insert that into the multi select - but I can't get the phrasing quite right

This is what I need the end result to look like (with varying numbers of sites)

And this is the code I am using to bring the data into the subform when a multiselect choice is made

//Count Subform Rows
varRowCount = 0;
for each row in SUB_LOCATIONS
{
if(row.ID != 0)
{
varRowCount = varRowCount + 1;
}
}
// Collect all the locations that are associated with this client and add to a collection
if(location[ID = input.locations].ID != null)
{
//create and clear the list
varCollection = Collection();
varCollection.clear();
//Add locations to the collection
varCollection.insertall(input.locations);
//Get the size of the collection (minus a one because it's a zero index)
varLocationCount = varCollection.size() - 1;
//Returns the ID of the last in the list
varLastLocation = varCollection.get(varLocationCount);
//Fetch the location about the chosen location
varFetchLocation = location[ID == varLastLocation];
//
// Now let's populate the subform
for each varLocation in varFetchLocation
{
//create the "varNewRow" variable for holding the new row data
varNewRow = Build_your_benchmark.SUB_LOCATIONS();
//
//Set the values for each row to the varNewRow variable
varNewRow.location_name=varFetchLocation.location_name;
varNewRow.benchmark_sector=varFetchLocation.benchmark_sector;
varNewRow.region=varFetchLocation.region;
varNewRow.occupants=varFetchLocation.occupants;
varNewRow.floor_area=varFetchLocation.floor_area;
//
//Insert "varNewRow" to new row on the subform
input.SUB_LOCATIONS.insert(varNewRow);
}
}