Query a feature layer (SQL)

Before starting this tutorial:

1. You need an ArcGIS Location Platform or ArcGIS Online account.

2. Your system meets the system requirements.

3. The ArcGIS Maps SDK for Qt, version 300.1.0 or later is installed.

4. The Qt 6.8.2 software development framework or later is installed.

5. The CMake build system is installed.

Option 1: Develop the code

To start the tutorial, complete the Display a map tutorial. This creates a map to display the Santa Monica Mountains in California using the topographic basemap from the ArcGIS Basemap Styles service The ArcGIS Basemap Styles service, also referred to as the Basemap Styles service, is a location service that provides basemap styles and data for the world. It returns styles as Mapbox styles and web maps, and data as vector tiles and/or map tiles. It supports all of the styles in the ArcGIS Basemap style and Open Basemap style family. An ArcGIS Location Platform or ArcGIS Online account is required to use the service. Learn more .

Open a Qt Creator project

1. Open the project you created by completing the Display a map tutorial.
2. Continue with the following instructions to execute a SQL query to return features from a feature layer based on spatial and attribute criteria.

Update the header file

This app will use various functions and member variables that need to be declared in the header file.

In the project Display_a_map > Display_a_map > Header Files folder of Qt Creator, double-click the Display_a_map.h file to open it. Forward declare the following classes.

namespace Esri::ArcGISRuntime {

class Map;

class MapQuickView;

class FeatureLayer;
class ServiceFeatureTable;
} // namespace Esri::ArcGISRuntime

Add the following code to define a function called runQuery that will be invokable from the GUI.

public:
    explicit Display_a_map(QObject* parent = nullptr);
    ~Display_a_map() override;

    Q_INVOKABLE void runQuery(const QString& expression);

Finally, declare the following private function and member variables. Then save the file.

private:
    Esri::ArcGISRuntime::MapQuickView* mapView() const;
    void setMapView(Esri::ArcGISRuntime::MapQuickView* mapView);

    void setupViewpoint();

    void addFeatureLayer();
    Esri::ArcGISRuntime::FeatureLayer* m_featureLayer = nullptr;
    Esri::ArcGISRuntime::ServiceFeatureTable* m_featureTable = nullptr;

Include header files in the source code

To create this app you will need to include several class header files from the ArcGIS Maps SDK for Qt C++ API.

In the project Display_a_map > Display_a_map > Source Files folder of Qt Creator, double-click the Display_a_map.cpp file to open it. Add the following include statements needed for this tutorial. Then save the file.

#include "Display_a_map.h"

#include "Map.h"

#include "MapTypes.h"

#include "MapQuickView.h"

#include "Point.h"
#include "Viewpoint.h"
#include "SpatialReference.h"
#include <QFuture>

#include "Envelope.h"
#include "Feature.h"
#include "FeatureLayer.h"
#include "LayerListModel.h"
#include "FeatureIterator.h"
#include "FeatureQueryResult.h"
#include "QueryParameters.h"
#include "SelectionProperties.h"
#include "ServiceFeatureTable.h"
#include <memory>
#include <QColor>
#include <QList>
#include <QUuid>
#include <QUrl>

Add a feature layer, query features, and select results

You will add three functions to add a feature layer from ArcGIS online, execute a query of that layer, and create a features list from the query result.

Staying within the Display_a_map.cpp file, add code to create the addFeatureLayer() function. This function adds the LA_County_Parcels feature layer hosted on ArcGIS Online to the map.

void Display_a_map::setupViewpoint()
{

    const Point center(-118.80543, 34.02700, SpatialReference::wgs84());
    const Viewpoint viewpoint(center, 100000.0);

    m_mapView->setViewpointAsync(viewpoint);

}

void Display_a_map::addFeatureLayer()
{
    // Create a ServiceFeatureTable from a QUrl.
    m_featureTable = new ServiceFeatureTable(QUrl("https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/LA_County_Parcels/FeatureServer/0"), this);

    // Create the feature layer using the feature table.
    m_featureLayer = new FeatureLayer(m_featureTable, this);

    // Add the feature layer to the map.
    m_map->operationalLayers()->append(m_featureLayer);
}

Continuing in the same file, add the runQuery(const QString& expression) function to implement the query that will execute a query of the parcels layer. This function creates a QueryParameters object that includes the currently visible map extent and a SQL expression, and then executes the query on the parcels table. When a query completes, the code iterates the returned results and adds those features to a list. That list is then used to select features in the parcels layer.

void Display_a_map::addFeatureLayer()
{
    // Create a ServiceFeatureTable from a QUrl.
    m_featureTable = new ServiceFeatureTable(QUrl("https://services3.arcgis.com/GVgbJbqm8hXASVYi/arcgis/rest/services/LA_County_Parcels/FeatureServer/0"), this);

    // Create the feature layer using the feature table.
    m_featureLayer = new FeatureLayer(m_featureTable, this);

    // Add the feature layer to the map.
    m_map->operationalLayers()->append(m_featureLayer);
}

void Display_a_map::runQuery(const QString& expression)
{
    if (!m_featureTable)
        return;

    // Create a query parameter object and set the WhereClause.
    QueryParameters queryParams;
    queryParams.setGeometry(m_mapView->currentViewpoint(ViewpointType::BoundingGeometry).targetGeometry().extent());
    queryParams.setWhereClause(expression);
    m_featureTable->queryFeaturesAsync(queryParams).then(this,[this](FeatureQueryResult* rawQueryResult)
     {
         if (!rawQueryResult)
             return;

         // Wrap the FeatureQueryResult in a unique_ptr to manage the memory effectively.
         auto queryResult = std::unique_ptr<FeatureQueryResult>(rawQueryResult);

         // Clear any existing selection.
         m_featureLayer->clearSelection();
         QList<Feature*> features;

         // Iterate over the result object.
         while(queryResult->iterator().hasNext())
         {
             Feature* feature = queryResult->iterator().next(this);
             // Add each feature to the list.
             features.append(feature);
         }
         // Select features.
         m_featureLayer->selectFeatures(features);
     });
}

Continuing within the Display_a_map.cpp file, locate the setMapView(MapQuickView* mapView) function. Modify the function to call the new addFeatureLayer() function and also set the color for displaying selected parcel layer features (or any other selection) in your map view. Note: by default, the selected features in the map view are displayed in cyan. Then save the file.

// Set the view (created in QML)
void Display_a_map::setMapView(MapQuickView* mapView)
{
    if (!mapView || mapView == m_mapView)
    {
        return;
    }

    m_mapView = mapView;
    m_mapView->setMap(m_map);

    addFeatureLayer();
    m_mapView->setSelectionProperties(SelectionProperties(QColor(Qt::yellow)));

    setupViewpoint();

    emit mapViewChanged();
}

Show a list of query expressions for the user to choose from

You will create a UI that allows the user to choose from a list of predefined query expressions. The expressions are presented in a ComboBox control and when the user makes a choice, the expression is passed to the runQuery method to find parcels that meet the selected criterion within the currently visible map extent.

In the project Display_a_map > Display_a_map > Resources > ../qml > qml.qrc > /qml folder of Qt Creator, double click the Display_a_mapForm.qml file to open it. Add the following code to create a ComboBox control to execute a predefined query expression.

    // Declare the C++ instance which creates the map etc. and supply the view
    Display_a_map {
        id: model
        mapView: view
    }

    ComboBox {
            id: queryComboBox
            anchors {
                left: parent.left
                top: parent.top
                margins: 15
            }

            property int bestWidth: implicitWidth
            width: bestWidth + leftPadding + rightPadding
            model: ["Choose a SQL where clause",
                "UseType = 'Government'",
                "UseType = 'Residential'",
                "UseType = 'Irrigated Farm'",
                "TaxRateArea = 10853",
                "TaxRateArea = 10860",
                "Roll_LandValue > 1000000",
                "Roll_LandValue < 1000000"]

            onCurrentTextChanged: {
                model.runQuery(queryComboBox.currentText)
            }
        }

Set developer credentials

For the final steps of this tutorial, click the tab below that corresponds to the authentication type (API key authentication or User authentication) that you chose when you completed the Display a map tutorial.

Be sure to also provide the same authentication (API key or user authentication Client ID/Redirect URL) that you used for the Display a map tutorial.

    // The following methods grant an access token:

    // 1. User authentication: Grants a temporary access token associated with a user's ArcGIS account.
    // To generate a token, a user logs in to the app with an ArcGIS account that is part of an
    // organization in ArcGIS Online or ArcGIS Enterprise.

    // 2. API key authentication: Get a long-lived access token that gives your application access to
    // ArcGIS location services. Go to the tutorial at https://links.esri.com/create-an-api-key.
    // Copy the API Key access token.

    const QString accessToken = QString("");

    if (accessToken.isEmpty())
    {
        qWarning()
            << "Use of ArcGIS location services, such as the basemap styles service, requires"
            << "you to authenticate with an ArcGIS account or set the API Key property.";
    }
    else
    {
        ArcGISRuntimeEnvironment::setApiKey(accessToken);
    }

# TODO: Replace the <path_to_toolkit_repo> with a valid location where the Qt Toolkit
# root directory resides on your system, example: C:/applications/arcgis-maps-sdk-toolkit-qt
# The code also sets the TOOLKIT_FOUND variable which is used by other parts of the tutorial.

set(ARCGIS_TOOLKIT_REPOSITORY "<path_to_toolkit_repo>")

{

#ifdef TOOLKIT_FOUND

    // Define the Redirect URL string obtained when creating the OAuth credentials.
    // TODO: You need to replace the "REDIRECT_URL" with your own valid string,
    // ex: "urn:ietf:wg:oauth:2.0:oob"

    const auto qStringRedirectUrl = QString{"REDIRECT_URL"};

    // Define the URL of the portal to authenticate with.
    const QUrl qUrlPortal = QUrl{"https://www.arcgis.com/"};

    // Define a unique identifier associated with an application registered with the
    // portal that assists with client/server OAuth authentication.
    // TODO: You need to replace the "CLIENT_ID" with your own valid string.

    const QString qStringClientId = QString{"CLIENT_ID"};

    // Create a new OAuth user configuration using: the Url to mapping web service, the Client ID
    // string, and the Redirect Url string.
    auto* oAuthUserConfiguration = new OAuthUserConfiguration(qUrlPortal, qStringClientId,
                                                              qStringRedirectUrl, this);

    // Call the Toolkit's OAuthUserConfigurationManager static `addConfiguration`
    // method to use the OAuth dialog. This will tell the Authenticator to use OAuth for the provided configuration.
    Toolkit::OAuthUserConfigurationManager::addConfiguration(oAuthUserConfiguration);
#endif // TOOLKIT_FOUND

Press Ctrl + R to run the app.

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.

Option 2: Download the solution

Click the Download solution link on this page under the Solution title and unzip the file to a location on your machine.

In Qt Creator, choose File > Open File or Project… from them menus. In the Open file dialog, navigate to the CMakeLists.txt file for the solution you unzipped and click the Open button.

The Configure Project window will appear for you to specify the Qt Kit to use to compile the project. Check on the Qt Kit called Desktop Qt 6.8.2 MSVC2022 64bit before clicking the Configure Project button at the bottom of the page.

Since the downloaded solution does not contain authentication credentials (API Key or User authentication), you must set up authentication to create the developer credentials and add them to the project.

For the final steps of this tutorial, click the tab below that corresponds to the authentication type (API key authentication or User authentication) that you chose when you completed the Display a map tutorial.

Be sure to also provide the same authentication (API key or user authentication Client ID/Redirect URL) that you used for the Display a map tutorial.

Set developer credentials in the solution

    // The following methods grant an access token:

    // 1. User authentication: Grants a temporary access token associated with a user's ArcGIS account.
    // To generate a token, a user logs in to the app with an ArcGIS account that is part of an
    // organization in ArcGIS Online or ArcGIS Enterprise.

    // 2. API key authentication: Get a long-lived access token that gives your application access to
    // ArcGIS location services. Go to the tutorial at https://links.esri.com/create-an-api-key.
    // Copy the API Key access token.

    const QString accessToken = QString("");

    if (accessToken.isEmpty())
    {
        qWarning()
            << "Use of ArcGIS location services, such as the basemap styles service, requires"
            << "you to authenticate with an ArcGIS account or set the API Key property.";
    }
    else
    {
        ArcGISRuntimeEnvironment::setApiKey(accessToken);
    }

# TODO: Replace the <path_to_toolkit_repo> with a valid location where the Qt Toolkit
# root directory resides on your system, example: C:/applications/arcgis-maps-sdk-toolkit-qt
# The code also sets the TOOLKIT_FOUND variable which is used by other parts of the tutorial.

set(ARCGIS_TOOLKIT_REPOSITORY "<path_to_toolkit_repo>")

{

#ifdef TOOLKIT_FOUND

    // Define the Redirect URL string obtained when creating the OAuth credentials.
    // TODO: You need to replace the "REDIRECT_URL" with your own valid string,
    // ex: "urn:ietf:wg:oauth:2.0:oob"

    const auto qStringRedirectUrl = QString{"REDIRECT_URL"};

    // Define the URL of the portal to authenticate with.
    const QUrl qUrlPortal = QUrl{"https://www.arcgis.com/"};

    // Define a unique identifier associated with an application registered with the
    // portal that assists with client/server OAuth authentication.
    // TODO: You need to replace the "CLIENT_ID" with your own valid string.

    const QString qStringClientId = QString{"CLIENT_ID"};

    // Create a new OAuth user configuration using: the Url to mapping web service, the Client ID
    // string, and the Redirect Url string.
    auto* oAuthUserConfiguration = new OAuthUserConfiguration(qUrlPortal, qStringClientId,
                                                              qStringRedirectUrl, this);

    // Call the Toolkit's OAuthUserConfigurationManager static `addConfiguration`
    // method to use the OAuth dialog. This will tell the Authenticator to use OAuth for the provided configuration.
    Toolkit::OAuthUserConfigurationManager::addConfiguration(oAuthUserConfiguration);
#endif // TOOLKIT_FOUND

Run the solution

Press Ctrl + R to run the app.

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.