RULE: whichIdentifier
if(
	isnull(ri!id1),
	ri!id2,
	ri!id1
)

RULE: main interface
load(
  local!gridSelection: a!gridSelection(
    pagingInfo: a!pagingInfo(
      startIndex: 1,
      batchSize: -1
    ) 
  ),
  local!dataSubset: todatasubset(
    {
      {id1: null, id2: "zzz1", value: "test 1"},
      {id1: null, id2: "zzz2", value: "test 2"},
      {id1: "abc3", id2: null, value: "test 3"},
      {id1: null, id2: "zzz4", value: "test 4"},
      {id1: "abc5", id2: null, value: "test 5"}
    },
    local!gridSelection.pagingInfo
  ),
  a!formLayout(
    label: "Grid identifier test",
    firstColumnContents: {
      a!gridField(
        columns: {
          a!gridTextColumn(
            label: "ID 1",
            field: "id1",
            data: index(local!dataSubset.data,"id1",{})
          ),
          a!gridTextColumn(
            label: "ID 2",
            field: "id2",
            data: index(local!dataSubset.data,"id2",{})
          ),
          a!gridTextColumn(
            label: "Value",
            field: "value",
            data: index(local!dataSubset.data,"value",{})
          )
        },
        totalCount: local!dataSubset.totalCount,
        value: local!gridSelection,
        saveinto: local!gridSelection,
        identifiers: apply(
          rule!whichIdentifier,
          merge(
            index(local!dataSubset.data,"id1",{}),
            index(local!dataSubset.data,"id2",{})
          )
        ),
        selection: true
      ),
      a!textField(
        label: "Selected",
        readOnly: true,
        value: local!gridSelection.selected
      )
    }
  )
)