Query a feature layer (SQL)

Learn how to execute a SQL query to return features from a feature layer based on spatial and attribute criteria.

A feature layer can contain a large number of features stored in ArcGIS. You can query a layer to access a subset of its features using any combination of spatial and attribute criteria. You can control whether or not each feature's geometry is returned, as well as which attributes are included in the results. Queries allow you to return a well-defined subset of your hosted data for analysis or display in your ArcGIS Runtime app.

In this tutorial, you'll write code to perform SQL queries that return a subset of features in the LA County Parcel feature layer (containing over 2.4 million features). Features that meet the query criteria are selected in the map.

Prerequisites

Steps

Open the Xcode project

1. To start the tutorial, complete the Display a map tutorial or download and unzip the solution.

2. Open the .xcodeproj file in Xcode.

3. If you downloaded the solution, get an access token and set the API key.

   Instructions to set the API Key

   An API Key gives your app access to secure resources used in this tutorial.

   1. Go to the Create an API key tutorial to obtain a new API key access token. Ensure that the following privilege is enabled: Location services > Basemaps > Basemap styles service. Copy the access token as it will be used in the next step.

   2. In Xcode, in the Project Navigator, click AppDelegate.swift.

   3. In the editor, set the APIKey property on the AGSArcGISRuntimeEnvironment with your access token.

      AppDelegate.swift

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          func application(_ application: UIApplication,
                           didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
      
              AGSArcGISRuntimeEnvironment.apiKey = "YOUR_ACCESS_TOKEN"
      
              return true
          }
      

      Expand

Set selection properties

Define the selection color via the map view's AGSSelectionProperties to distinguish selected features in the map view.

1. In Xcode, in the Project Navigator, click ViewController.swift.

2. Update the setupMap() method to set map view's selection color to be yellow. This step is optional, and if you don't set a selection color, cyan is used as the default.

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       private func setupMap() {
           mapView.map = map
           mapView.setViewpoint(
               AGSViewpoint(
                   latitude: 34.02700,
                   longitude: -118.80500,
                   scale: 72_000
               )
           )
   
           // Set selection color.
           mapView.selectionProperties.color = .yellow
   
       }
   

Add a parcels layer to the map

Access the LA parcels feature service and create a new layer to display those features in the map.

1. In ViewController.swift, create a property for an AGSServiceFeatureTable to access LA parcels after the mapView property declaration.

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       @IBOutlet var mapView: AGSMapView!
       private let map = AGSMap(basemapStyle: .arcGISTopographic)
   
       let featureTable = AGSServiceFeatureTable(url: URL(string: "https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/LA_County_Parcels/FeatureServer/0")!)
   
   

2. Create a new method, setupLayer(). Create an AGSFeatureLayer and add it to the map's list of operational layers to view the parcels.

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       private func setupLayer() {
           // Add feature layer to map's operational layers.
           let parcelsFeatureLayer = AGSFeatureLayer(featureTable: featureTable)
           mapView.map?.operationalLayers.add(parcelsFeatureLayer)
       }
   

3. Update the viewDidLoad() method with a call to setupLayer().

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       override func viewDidLoad() {
           super.viewDidLoad()
           setupMap()
   
           setupLayer()
   
       }
   

4. Press Command + R to run the app.

   More info

   If you are using the Xcode simulator your system must meet these minimum requirements: macOS Big Sur 11.3, Xcode 13, iOS 13. If you are using a physical device, then refer to the system requirements.

The app loads with the map centered on the Santa Monica Mountains in California with the parcels feature layer displayed.

Create a UI control to display predefined query strings

To make performing a query on a feature layer flexible, add a UI control to present a list of predefined attribute queries for the parcels dataset.

1. Create a UIButton and define its properties.

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       @IBOutlet var mapView: AGSMapView!
       private let map = AGSMap(basemapStyle: .arcGISTopographic)
   
       let featureTable = AGSServiceFeatureTable(url: URL(string: "https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/LA_County_Parcels/FeatureServer/0")!)
   
       let optionsButton: UIButton = {
           let button = UIButton()
           button.backgroundColor = .lightGray
           button.setTitleColor(.blue, for: .normal)
           button.setTitle("Choose a SQL 'where' clause", for: .normal)
           button.translatesAutoresizingMaskIntoConstraints = false
           return button
       }()
   

2. Create a new method, setupButton(), and add the button as a subView of the main view. This displays the button when the app is run.

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       private func setupButton() {
   
           // Add button as subview to the view.
           view.addSubview(optionsButton)
   
       }
   

3. Next, add layout constraints to define the position of the button relative to the main view and safeArea of the device. This ensures the button looks as expected in different devices and orientations.

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       private func setupButton() {
   
           // Add button as subview to the view.
           view.addSubview(optionsButton)
   
           // Add layout constraints defining the position of the button
           optionsButton.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
           optionsButton.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
           optionsButton.rightAnchor.constraint(equalTo: view.rightAnchor).isActive = true
           optionsButton.heightAnchor.constraint(equalToConstant: 60 + self.view.safeAreaInsets.bottom).isActive = true
   
       }
   

4. Next, add a target for the button with the method to execute when it is tapped. This method, populateOptions(), which you'll create in the next section, populates and displays a list of query options.

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       private func setupButton() {
   
           // Add button as subview to the view.
           view.addSubview(optionsButton)
   
           // Add layout constraints defining the position of the button
           optionsButton.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
           optionsButton.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
           optionsButton.rightAnchor.constraint(equalTo: view.rightAnchor).isActive = true
           optionsButton.heightAnchor.constraint(equalToConstant: 60 + self.view.safeAreaInsets.bottom).isActive = true
   
           // Define method to call when button is tapped.
           optionsButton.addTarget(self, action: #selector(populateOptions), for: .touchUpInside)
   
       }
   

5. Update the viewDidLoad() method with a call to setupButton().

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       override func viewDidLoad() {
           super.viewDidLoad()
           setupMap()
   
           setupLayer()
   
           setupButton()
   
       }
   

You can also create and set up the UIButton using storyboards.

Create predefined query expressions

You'll now create and present a list of query options for the user to choose from when the button is tapped.

1. To populate the UI with a predefined list of where clauses for the query, create a new method called populateOptions().

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       @objc func populateOptions() {
   
       }
   

2. Create an UIAlertController with a title and of style actionSheet. Create an array of strings to populate the where clauses. Create an alert action for each where clause, which calls the method to execute the query when chosen. You'll implement the method executeQuery(whereClause:) later.

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       @objc func populateOptions() {
   
           // Populate query options.
           let alert = UIAlertController(title: "Choose a SQL where clause.", message: nil, preferredStyle: .actionSheet)
           let whereClauses = ["UseType = 'Government'", "UseType = 'Residential'", "UseType = 'Irrigated Farm'", "TaxRateArea = 10853", "TaxRateArea = 10860", "Roll_LandValue > 1000000", "Roll_LandValue < 1000000"]
           whereClauses.forEach { whereClause in
               let action = UIAlertAction(title: whereClause, style: .default) { [unowned self] _ in
                   executeQuery(whereClause: whereClause)
               }
               alert.addAction(action)
           }
   
       }
   

3. Add code to present the options to the user.

   ViewController.swift

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       @objc func populateOptions() {
   
           // Populate query options.
           let alert = UIAlertController(title: "Choose a SQL where clause.", message: nil, preferredStyle: .actionSheet)
           let whereClauses = ["UseType = 'Government'", "UseType = 'Residential'", "UseType = 'Irrigated Farm'", "TaxRateArea = 10853", "TaxRateArea = 10860", "Roll_LandValue > 1000000", "Roll_LandValue < 1000000"]
           whereClauses.forEach { whereClause in
               let action = UIAlertAction(title: whereClause, style: .default) { [unowned self] _ in
                   executeQuery(whereClause: whereClause)
               }
               alert.addAction(action)
           }
   
           // Present query options.
           alert.popoverPresentationController?.sourceView = optionsButton
           alert.popoverPresentationController?.sourceRect = optionsButton.frame
           alert.preferredContentSize = CGSize(width: 300, height: 200)
           present(alert, animated: true)
   
       }
   

Add a method to execute the query

In this step, create a new method that queries the parcels AGSFeatureLayer using both attribute and spatial criteria. After clearing any currently selected features, a new query will be executed to find features in the map's current extent that meet the selected attribute expression. The features in the AGSFeatureQueryResult will be selected in the parcels layer.

1. Add the executeQuery function to query parcels using a provided where expression.

   ViewController.swift

   Use dark colors for code blocks

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       func executeQuery(whereClause: String) {
           // Get the parcels layer from the map
           guard let parcelsFeatureLayer = map.operationalLayers.firstObject as? AGSFeatureLayer else {
               //... handle error
               return
           }
   
           // Clear any existing selection.
           parcelsFeatureLayer.clearSelection()
   
           // Create the query parameters using the where expression and extent passed in.
           let queryParams = AGSQueryParameters()
           queryParams.whereClause = whereClause
           queryParams.geometry = mapView.visibleArea?.extent
           queryParams.returnGeometry = true
   
           featureTable.queryFeatures(with: queryParams) { queryResult, error in
               if let _ = error {
                   //... handle error
               } else if let features = queryResult?.featureEnumerator().allObjects as? [AGSArcGISFeature] {
                   parcelsFeatureLayer.select(features)
               }
           }
       }
   

Run the app

1. Press Command + R to run the app.

   More info

   If you are using the Xcode simulator your system must meet these minimum requirements: macOS Big Sur 11.3, Xcode 13, iOS 13. If you are using a physical device, then refer to the system requirements.

2. The app loads with the map centered on the Santa Monica Mountains in California with the parcels feature layer displayed. Choose an attribute expression, and parcels in the current extent that meet the selected criteria will display in the specified selection color.

What's next?

Learn how to use additional API features, ArcGIS location services, and ArcGIS tools in these tutorials:

• Add a point, line, and polygon
• Add a feature layer