Multi Drop Down Validation

You can conditionally manage the choice labels in the second dropdown based on the value selected at the first dropdown. 
can you share the code of the dropdown components, so that the community could get better insight of the use case.

a!localVariables(
  local!savedValueIndex,
  local!firstDropdownSavedValue,
  local!secondDropdownSavedValue,
  local!choiceLabels1: {
    "Corporate",
    "Engineer",
  },
  local!choiceValues1: { 1, 2 },
  local!choiceLabels2: {
    "Corporate",
    "Engineer",
  },
  local!choiceValues2: { 1, 2},
  {
    a!dropdownField(
      label: "Dropdown",
      labelPosition: "ABOVE",
      placeholder: "--- Select a Value ---",
      choiceLabels: local!choiceLabels1,
      choiceValues: local!choiceValues1,
      value: local!firstDropdownSavedValue,
      saveInto: {
        a!save(local!savedValueIndex, index(local!choiceValues1, save!value, null)),
        a!save(local!firstDropdownSavedValue, save!value)
      },
      searchDisplay: "AUTO",
      validations: {}
    ),
    a!dropdownField(
      label: "Dropdown",
      labelPosition: "ABOVE",
      placeholder: "--- Select a Value ---",
      choiceLabels: if(
        a!isNullOrEmpty(local!savedValueIndex),
        local!choiceLabels2,
        remove(local!choiceLabels2, local!savedValueIndex)
      ),
      choiceValues: if(
        a!isNullOrEmpty(local!savedValueIndex),
        local!choiceValues2,
        remove(local!choiceValues2, local!savedValueIndex)
      ),
      saveInto: {
        a!save(local!secondDropdownSavedValue, save!value)
      },
      searchDisplay: "AUTO",
      validations: {},
      value: local!secondDropdownSavedValue
    )
  }
)

Please refer the code to figure out the logic to conditionally manage the choice labels and values.

Hi there,

You can add a validation when a single value has been selected more than once. You can use wherecontains function and use it on the CDT/Dict field. If it returns more than one item, then you could show a validation.