How do I call upon a dependent dropdown field?

Question

Hi all! 
 New to Appian, and I am stuck on figuring out how to correct configure a dependent dropdown. 
 The first dropdown field is called "Plant," and its fields consist of plantId, value, & description. The second dropdown field is called "Storage Location," and its fields consist of werks, name1, & land1. Both queries have one similar field, which is "value" and "werks," but I need to call back "plantid." How would I do that? 
 Thanks!

Shubham Aware · Answer

Use the selected plantId to lookup its corresponding value field from plantData, then filter storageData where werks matches that value to populate the dependent Storage Location dropdown. a!localVariables(
 /* Sample Plant Data */
 local!plantData: {
 a!map(plantId: 1, value: "P100", description: "Plant Chicago"),
 a!map(plantId: 2, value: "P200", description: "Plant Dallas"),
 a!map(plantId: 3, value: "P300", description: "Plant Boston")
 },
 /* Sample Storage Location Data */
 local!storageData: {
 a!map(werks: "P100", name1: "Warehouse A", land1: "USA"),
 a!map(werks: "P100", name1: "Warehouse B", land1: "USA"),
 a!map(werks: "P200", name1: "Storage Unit 1", land1: "USA"),
 a!map(werks: "P200", name1: "Storage Unit 2", land1: "USA"),
 a!map(werks: "P300", name1: "Depot North", land1: "USA"),
 a!map(werks: "P300", name1: "Depot South", land1: "USA")
 },
 /* Variables to store selections */
 local!selectedPlantId: null,
 local!selectedStorageLocation: null,
 /* Get the value field of selected plant */
 local!selectedPlantValue: if(
 a!isNullOrEmpty(local!selectedPlantId),
 null,
 index(
 local!plantData.value,
 wherecontains(local!selectedPlantId, local!plantData.plantId),
 null
 )
 ),
 /* Filter storage locations based on selected plant */
 local!filteredStorageLocations: if(
 a!isNullOrEmpty(local!selectedPlantValue),
 {},
 index(
 local!storageData,
 wherecontains(local!selectedPlantValue, local!storageData.werks),
 {}
 )
 ),
 /* Form Layout */
 a!formLayout(
 titleBar: "Plant and Storage Selection",
 contents: {
 /* Plant Dropdown */
 a!dropdownField(
 label: "Plant",
 placeholder: "-- Select Plant --",
 choiceLabels: local!plantData.description,
 choiceValues: local!plantData.plantId,
 value: local!selectedPlantId,
 saveInto: {
 local!selectedPlantId,
 a!save(local!selectedStorageLocation, null)
 },
 required: true
 ),
 /* Storage Location Dropdown - FIXED */
 a!dropdownField(
 label: "Storage Location",
 placeholder: "-- Select Storage Location --",
 disabled: a!isNullOrEmpty(local!selectedPlantId),
 choiceLabels: if(
 a!isNullOrEmpty(local!filteredStorageLocations),
 {},
 local!filteredStorageLocations.name1
 ),
 choiceValues: if(
 a!isNullOrEmpty(local!filteredStorageLocations),
 {},
 local!filteredStorageLocations.name1
 ),
 value: local!selectedStorageLocation,
 saveInto: local!selectedStorageLocation,
 required: true
 )
 }
 )
)