Query with CQL filters

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Query data from an OGC API feature service using CQL filters.

Image of Query with CQL Filters

Use case

CQL (Common Query Language) is an OGC-created query language used to query for subsets of features. Use CQL filters to narrow geometry results from an OGC feature table.

How to use the sample

Enter a CQL query. Press the "Apply query" button to see the query applied to the OGC API features shown on the map.

How it works

  1. Create an OgcFeatureCollectionTable object using a URL to an OGC API feature service and a collection ID.
  2. Create a QueryParameters object.
  3. Set the QueryParameters.WhereClause property.
  4. Set the QueryParameters.MaxFeatures property.
  5. Create Datetime objects for the start time and end time being queried.
  6. Create a TimeExtent object using the start and end Datetime objects. Set the QueryParameters.TimeExtent property
  7. Populate the OgcFeatureCollectionTable using PopulateFromServiceAsync() with the custom QueryParameters created in the previous steps.
  8. Use MapView.SetViewpointGeometryAsync() with the OgcFeatureCollectionTable.Extent to view the newly-queried features.

Relevant API

  • OgcFeatureCollectionTable
  • QueryParameters
  • TimeExtent

About the data

The Daraa, Syria test data is OpenStreetMap data converted to the Topographic Data Store schema of NGA.

Additional information

See the OGC API website for more information on the OGC API family of standards. See the CQL documentation to learn more about the common query language.

Tags

browse, catalog, common query language, CQL, feature table, filter, OGC, OGC API, query, service, web

Sample Code

QueryCQLFilters.cs
                                                                                                                                                                                                                                                                                                                                                                                
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// Copyright 2021 Esri.
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License.
// You may obtain a copy of the License at: http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific
// language governing permissions and limitations under the License.

using ArcGISRuntime;
using Esri.ArcGISRuntime.Data;
using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Symbology;
using Esri.ArcGISRuntime.UI.Controls;
using Foundation;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using UIKit;
using Color = System.Drawing.Color;

namespace ArcGISRuntimeXamarin.Samples.QueryCQLFilters
{
    [Register("QueryCQLFilters")]
    [ArcGISRuntime.Samples.Shared.Attributes.Sample(
        name: "Query with CQL filters",
        category: "Layers",
        description: "Query data from an OGC API feature service using CQL filters.",
        instructions: "Enter a CQL query. Press the \"Apply query\" button to see the query applied to the OGC API features shown on the map.",
        tags: new[] { "CQL", "OGC", "OGC API", "browse", "catalog", "common query language", "feature table", "filter", "query", "service", "web", "Featured" })]
    public class QueryCQLFilters : UIViewController
    {
        // Hold references to UI controls.
        private MapView _myMapView;
        private UIActivityIndicatorView _activityIndicator;
        private UISwitch _dateSwitch;
        private UITextField _maxFeaturesEntry;
        private UIButton _clauseButton;
        private UIBarButtonItem _applyButton;
        private UIBarButtonItem _resetButton;
        private UIDatePicker _startDatePicker;
        private UIDatePicker _endDatePicker;
        private UIToolbar _applyToolbar;

        private List<string> _whereClauses { get; } = new List<string>
        {
            // Sample Query 1: Query for features with an F_CODE attribute property of "AP010".
            "F_CODE = 'AP010'", // cql-text query
            "{ \"eq\" : [ { \"property\" : \"F_CODE\" }, \"AP010\" ] }", // cql-json query

            // Sample Query 2: Query for features with an F_CODE attribute property similar to "AQ".
            "F_CODE LIKE 'AQ%'", // cql-text query

            // Sample Query 3: use cql-json to combine "before" and "eq" operators with the logical "and" operator.
           "{\"and\":[{\"eq\":[{ \"property\" : \"F_CODE\" }, \"AP010\"]},{ \"before\":[{ \"property\" : \"ZI001_SDV\"},\"2013-01-01\"]}]}"
        };

        // Hold a reference to the OGC feature collection table.
        private OgcFeatureCollectionTable _featureTable;

        // Constants for the service URL and collection id.
        private const string ServiceUrl = "https://demo.ldproxy.net/daraa";

        // Note that the service defines the collection id which can be accessed via OgcFeatureCollectionInfo.CollectionId.
        private const string CollectionId = "TransportationGroundCrv";

        private string _whereClause;

        public QueryCQLFilters()
        {
            Title = "Query with CQL filters";
        }

        private async Task Initialize()
        {
            try
            {
                // Populate the UI.
                _maxFeaturesEntry.Text = "3000";
                _startDatePicker.Date = (NSDate)new DateTime(2011, 6, 13).ToUniversalTime();
                _endDatePicker.Date = (NSDate)new DateTime(2012, 1, 7).ToUniversalTime();

                // Create the map with topographic basemap.
                _myMapView.Map = new Map(BasemapStyle.ArcGISTopographic);

                _activityIndicator.StartAnimating();

                // Create the feature table from URI and collection id.
                _featureTable = new OgcFeatureCollectionTable(new Uri(ServiceUrl), CollectionId);

                // Set the feature request mode to manual (only manual is currently supported).
                // In this mode, you must manually populate the table - panning and zooming won't request features automatically.
                _featureTable.FeatureRequestMode = FeatureRequestMode.ManualCache;

                // Load the table.
                await _featureTable.LoadAsync();

                // Populate the OGC feature collection table.
                QueryParameters queryParamaters = new QueryParameters();
                queryParamaters.MaxFeatures = 3000;
                await _featureTable.PopulateFromServiceAsync(queryParamaters, false, null);

                // Create a feature layer from the OGC feature collection
                // table to visualize the OAFeat features.
                FeatureLayer ogcFeatureLayer = new FeatureLayer(_featureTable);

                // Set a renderer for the layer.
                ogcFeatureLayer.Renderer = new SimpleRenderer(new SimpleLineSymbol(SimpleLineSymbolStyle.Solid, Color.Red, 1.5));

                // Add the layer to the map.
                _myMapView.Map.OperationalLayers.Add(ogcFeatureLayer);

                // Zoom to the extent of the feature layer/table.
                Envelope tableExtent = _featureTable.Extent;
                if (tableExtent != null && !tableExtent.IsEmpty)
                {
                    await _myMapView.SetViewpointGeometryAsync(tableExtent, 20);
                }
            }
            catch (Exception ex)
            {
                new UIAlertView(ex.GetType().Name, ex.Message, (IUIAlertViewDelegate)null, "Ok", null).Show();
            }
            finally
            {
                // Update the UI.
                _activityIndicator.StopAnimating();
            }
        }

        public QueryParameters CreateQueryParameters()
        {
            // Create new query parameters.
            var queryParameters = new QueryParameters();

            // Assign the where clause if one is provided.
            if (!string.IsNullOrEmpty(_whereClause)) queryParameters.WhereClause = _whereClause;

            // Set the MaxFeatures property to MaxFeaturesBox content.
            if (int.TryParse(_maxFeaturesEntry.Text, out int parsedMaxFeatures))
                queryParameters.MaxFeatures = parsedMaxFeatures;

            // Set user date times if provided.
            if (_dateSwitch.On)
            {
                DateTime startDate = (_startDatePicker.Date != null) ? (DateTime)_startDatePicker.Date : DateTime.MinValue;
                DateTime endDate = (_endDatePicker.Date != null) ? (DateTime)_endDatePicker.Date : new DateTime(9999, 12, 31);

                // Use the newly created startDate and endDate to create the TimeExtent.
                queryParameters.TimeExtent = new Esri.ArcGISRuntime.TimeExtent(startDate, endDate);
            }

            return queryParameters;
        }

        private void ResetClicked(object sender, EventArgs e)
        {
            _whereClause = null;
            _clauseButton.SetTitle("Select Clause", UIControlState.Normal);
            _maxFeaturesEntry.Text = "3000";
            _dateSwitch.On = true;
            _startDatePicker.Date = (NSDate)new DateTime(2011, 6, 13).ToUniversalTime();
            _endDatePicker.Date = (NSDate)new DateTime(2012, 1, 7).ToUniversalTime();
        }

        private async void ApplyClicked(object sender, EventArgs e)
        {
            if (_featureTable.LoadStatus != Esri.ArcGISRuntime.LoadStatus.Loaded)
            {
                return;
            }

            try
            {
                _activityIndicator.StartAnimating();

                // Set queryParameters to the user's input
                var queryParameters = CreateQueryParameters();

                // Populate the table with the query, clearing the exist content of the table.
                // Setting outFields to null requests all fields.
                var result = await _featureTable.PopulateFromServiceAsync(queryParameters, true, outFields: null);

                // Zoom to the extent of the returned features.
                Envelope tableExtent = GeometryEngine.CombineExtents(result.Select(feature => feature.Geometry));
                if (tableExtent != null && !tableExtent.IsEmpty)
                {
                    await _myMapView.SetViewpointGeometryAsync(tableExtent, 20);
                }

                // Report the number of returned features by the query.
                new UIAlertView("Query Completed", $"Query returned {result.Count()} features.", (IUIAlertViewDelegate)null, "Ok", null).Show();
            }
            catch (Exception ex)
            {
                new UIAlertView(ex.GetType().Name, ex.Message, (IUIAlertViewDelegate)null, "Ok", null).Show();
            }
            finally
            {
                // Update the UI.
                _activityIndicator.StopAnimating();
            }
        }

        private void DateSwitched(object sender, EventArgs e)
        {
            _startDatePicker.Enabled = _endDatePicker.Enabled = _dateSwitch.On;
        }

        private void ClauseClick(object sender, EventArgs ev)
        {
            // Start the UI for the user choosing the clause.
            UIAlertController prompt = UIAlertController.Create(null, "Choose clause", UIAlertControllerStyle.ActionSheet);

            foreach (string clause in _whereClauses)
            {
                prompt.AddAction(UIAlertAction.Create(clause, UIAlertActionStyle.Default, ClauseSelected));
            }

            // Needed to prevent crash on iPad.
            UIPopoverPresentationController ppc = prompt.PopoverPresentationController;
            if (ppc != null)
            {
                ppc.SourceView = _applyToolbar;
                ppc.PermittedArrowDirections = UIPopoverArrowDirection.Down;
            }

            PresentViewController(prompt, true, null);
        }

        private void ClauseSelected(UIAlertAction obj)
        {
            _whereClause = obj.Title;
            _clauseButton.SetTitle(obj.Title, UIControlState.Normal);
        }

        public override void LoadView()
        {
            // Create the views.
            View = new UIView { BackgroundColor = ApplicationTheme.BackgroundColor };

            _myMapView = new MapView();
            _myMapView.TranslatesAutoresizingMaskIntoConstraints = false;

            _activityIndicator = new UIActivityIndicatorView(UIActivityIndicatorViewStyle.WhiteLarge)
            {
                TranslatesAutoresizingMaskIntoConstraints = false,
                HidesWhenStopped = true,
                BackgroundColor = UIColor.FromWhiteAlpha(0, .5f)
            };

            UILabel clauseLabel = new UILabel { Text = "Where clause:", TranslatesAutoresizingMaskIntoConstraints = false };
            _clauseButton = new UIButton() { TranslatesAutoresizingMaskIntoConstraints = false };
            _clauseButton.SetTitle("Select Clause", UIControlState.Normal);
            _clauseButton.SetTitleColor(View.TintColor, UIControlState.Normal);
            var clauseStack = GetRowStackView(new UIView[] { clauseLabel, _clauseButton });

            UILabel maxLabel = new UILabel { Text = "Maximum features:", TranslatesAutoresizingMaskIntoConstraints = false };
            _maxFeaturesEntry = new UITextField { TranslatesAutoresizingMaskIntoConstraints = false, Text = "3000" };
            var maxFeaturesStack = GetRowStackView(new UIView[] { maxLabel, _maxFeaturesEntry });

            UILabel dateLabel = new UILabel { Text = "Time extent:", TranslatesAutoresizingMaskIntoConstraints = false };
            _dateSwitch = new UISwitch { TranslatesAutoresizingMaskIntoConstraints = false, On = true };
            var dateSwitchStack = GetRowStackView(new UIView[] { dateLabel, _dateSwitch });

            _startDatePicker = new UIDatePicker { PreferredDatePickerStyle = UIDatePickerStyle.Compact, Mode = UIDatePickerMode.Date };
            _endDatePicker = new UIDatePicker { PreferredDatePickerStyle = UIDatePickerStyle.Compact, Mode = UIDatePickerMode.Date };
            var datesStack = GetRowStackView(new UIView[] { _startDatePicker, _endDatePicker });

            _applyButton = new UIBarButtonItem { Title = "Apply" };
            _resetButton = new UIBarButtonItem { Title = "Reset" };

            _applyToolbar = new UIToolbar { TranslatesAutoresizingMaskIntoConstraints = false };
            _applyToolbar.Items = new[]
            {
                _applyButton,
                new UIBarButtonItem(UIBarButtonSystemItem.FlexibleSpace),
                _resetButton
            };

            // Add the views.
            View.AddSubviews(_myMapView, dateSwitchStack, maxFeaturesStack, clauseStack, datesStack, _applyToolbar, _activityIndicator);

            // Lay out the views.
            NSLayoutConstraint.ActivateConstraints(new[]{
                _myMapView.TopAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.TopAnchor),
                _myMapView.BottomAnchor.ConstraintEqualTo(clauseStack.TopAnchor),
                _myMapView.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
                _myMapView.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor),

                clauseStack.TopAnchor.ConstraintEqualTo(_myMapView.BottomAnchor),
                clauseStack.BottomAnchor.ConstraintEqualTo(maxFeaturesStack.TopAnchor),
                clauseStack.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
                clauseStack.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor),

                maxFeaturesStack.TopAnchor.ConstraintEqualTo(clauseStack.BottomAnchor),
                maxFeaturesStack.BottomAnchor.ConstraintEqualTo(dateSwitchStack.TopAnchor),
                maxFeaturesStack.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
                maxFeaturesStack.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor),

                dateSwitchStack.TopAnchor.ConstraintEqualTo(maxFeaturesStack.BottomAnchor),
                dateSwitchStack.BottomAnchor.ConstraintEqualTo(datesStack.TopAnchor),
                dateSwitchStack.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
                dateSwitchStack.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor),

                datesStack.TopAnchor.ConstraintEqualTo(dateSwitchStack.BottomAnchor),
                datesStack.BottomAnchor.ConstraintEqualTo(_applyToolbar.TopAnchor),
                datesStack.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
                datesStack.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor),

                datesStack.HeightAnchor.ConstraintEqualTo(45),

                _applyToolbar.TopAnchor.ConstraintEqualTo(datesStack.BottomAnchor),
                _applyToolbar.BottomAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.BottomAnchor),
                _applyToolbar.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
                _applyToolbar.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor),

                _activityIndicator.TopAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.TopAnchor),
                _activityIndicator.BottomAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.BottomAnchor),
                _activityIndicator.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
                _activityIndicator.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor),
            });
        }

        private UIStackView GetRowStackView(UIView[] views)
        {
            UIStackView row = new UIStackView(views);
            row.TranslatesAutoresizingMaskIntoConstraints = false;
            row.Spacing = 8;
            row.DirectionalLayoutMargins = new NSDirectionalEdgeInsets(5, 5, 5, 5);
            row.Axis = UILayoutConstraintAxis.Horizontal;
            row.Distribution = UIStackViewDistribution.EqualCentering;
            row.WidthAnchor.ConstraintEqualTo(350).Active = true;
            row.LayoutMarginsRelativeArrangement = true;
            return row;
        }

        public override void ViewDidLoad()
        {
            base.ViewDidLoad();
            _ = Initialize();
        }

        public override void ViewWillAppear(bool animated)
        {
            base.ViewWillAppear(animated);

            // Subscribe to events.
            _clauseButton.TouchUpInside += ClauseClick;
            _dateSwitch.ValueChanged += DateSwitched;
            _applyButton.Clicked += ApplyClicked;
            _resetButton.Clicked += ResetClicked;
        }

        public override void ViewDidDisappear(bool animated)
        {
            base.ViewDidDisappear(animated);

            // Unsubscribe from events, per best practice.
            _clauseButton.TouchUpInside -= ClauseClick;
            _dateSwitch.ValueChanged -= DateSwitched;
            _applyButton.Clicked -= ApplyClicked;
            _resetButton.Clicked -= ResetClicked;
        }
    }
}

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