Query data from an OGC API feature service using 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
- Create an
OgcFeatureCollectionTableobject using a URL to an OGC API feature service and a collection ID. - Create a
QueryParametersobject. - Set the
QueryParameters.WhereClauseproperty. - Set the
QueryParameters.MaxFeaturesproperty. - Create
Datetimeobjects for the start time and end time being queried. - Create a
TimeExtentobject using the start and endDatetimeobjects. Set theQueryParameters.TimeExtentproperty - Populate the
OgcFeatureCollectionTableusingPopulateFromServiceAsync()with the customQueryParameterscreated in the previous steps. - Use
MapView.SetViewpointGeometryAsync()with theOgcFeatureCollectionTable.Extentto 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
// 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 Android.App;
using Android.Content;
using Android.OS;
using Android.Widget;
using ArcGISRuntime;
using Esri.ArcGISRuntime.Data;
using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Symbology;
using Esri.ArcGISRuntime.UI.Controls;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Color = System.Drawing.Color;
namespace ArcGISRuntimeXamarin.Samples.QueryCQLFilters
{
[Activity(ConfigurationChanges = Android.Content.PM.ConfigChanges.Orientation | Android.Content.PM.ConfigChanges.ScreenSize)]
[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" })]
public class QueryCQLFilters : Activity
{
// Hold references to the UI controls.
private MapView _myMapView;
private Spinner _whereClauseSpinner;
private EditText _maxFeatures;
private Switch _dateSwitch;
private Button _applyButton;
private Button _resetButton;
private Button _startDateButton;
private Button _endDateButton;
private ProgressBar _progressBar;
private List<string> _whereClauses { get; } = new List<string>
{
// Empty query.
"",
// Sample Query 1: Query for features with an F_CODE attribute property of "AP010".
"{ \"op\": \"=\", \"args\": [ { \"property\": \"F_CODE\" }, \"AP010\" ] }", // cql2-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 cql2-json to combine "before" and "eq" operators with the logical "and" operator.
"{\"op\": \"and\", \"args\":[{ \"op\": \"=\", \"args\":[{ \"property\" : \"F_CODE\" }, \"AP010\"]}, { \"op\": \"t_before\", \"args\":[{ \"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 DateTime? _startTime = new DateTime(2011, 6, 13);
private DateTime? _endTime = new DateTime(2012, 1, 7);
private TaskCompletionSource<DateTime> _dateTimeTCS;
protected override void OnCreate(Bundle bundle)
{
base.OnCreate(bundle);
Title = "Query with CQL filters";
CreateLayout();
_ = Initialize();
}
private async Task Initialize()
{
// Populate the UI.
var adapter = new ArrayAdapter(this, Android.Resource.Layout.SimpleSpinnerItem, _whereClauses);
_whereClauseSpinner.Adapter = adapter;
_maxFeatures.Text = "3000";
_startDateButton.Text = ((DateTime)_startTime).ToShortDateString();
_endDateButton.Text = ((DateTime)_endTime).ToShortDateString();
// Create the map with topographic basemap.
_myMapView.Map = new Map(BasemapStyle.ArcGISTopographic);
try
{
_progressBar.Visibility = Android.Views.ViewStates.Visible;
// 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 AlertDialog.Builder(this).SetMessage(ex.Message).SetTitle(ex.GetType().Name).Show();
}
finally
{
// Update the UI.
_progressBar.Visibility = Android.Views.ViewStates.Gone;
}
}
public QueryParameters CreateQueryParameters()
{
// Create new query parameters.
var queryParameters = new QueryParameters();
// Assign the where clause if one is provided.
if (_whereClauseSpinner.SelectedItem?.ToString() is string selectedClause)
{
queryParameters.WhereClause = selectedClause;
}
// Set the MaxFeatures property to MaxFeaturesBox content.
if (int.TryParse(_maxFeatures.Text, out int parsedMaxFeatures))
{
queryParameters.MaxFeatures = parsedMaxFeatures;
}
// Set user date times if provided.
if (_dateSwitch.Checked)
{
DateTime startDate = (_startTime is DateTime userStart) ? userStart : DateTime.MinValue;
DateTime endDate = (_endTime is DateTime userEnd) ? userEnd : 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 CreateLayout()
{
// Load the layout from the xml resource.
SetContentView(Resource.Layout.QueryCQLFilters);
_myMapView = FindViewById<MapView>(Resource.Id.MapView);
_whereClauseSpinner = FindViewById<Spinner>(Resource.Id.whereClauseSpinner);
_maxFeatures = FindViewById<EditText>(Resource.Id.maxFeatures);
_dateSwitch = FindViewById<Switch>(Resource.Id.dateSwitch);
_startDateButton = FindViewById<Button>(Resource.Id.startDateButton);
_endDateButton = FindViewById<Button>(Resource.Id.endDateButton);
_applyButton = FindViewById<Button>(Resource.Id.applyButton);
_resetButton = FindViewById<Button>(Resource.Id.resetButton);
_progressBar = FindViewById<ProgressBar>(Resource.Id.progressBar);
_dateSwitch.CheckedChange += DateSwitchChanged;
_startDateButton.Click += StartDateClick;
_endDateButton.Click += EndDateClick;
_applyButton.Click += ApplyQuery;
_resetButton.Click += ResetQuery;
}
private void ResetQuery(object sender, EventArgs e)
{
_whereClauseSpinner.SetSelection(0);
_maxFeatures.Text = "3000";
_dateSwitch.Checked = true;
_startTime = new DateTime(2011, 6, 13);
_endTime = new DateTime(2012, 1, 7);
_startDateButton.Text = ((DateTime)_startTime).ToShortDateString();
_endDateButton.Text = ((DateTime)_endTime).ToShortDateString();
}
private async void ApplyQuery(object sender, EventArgs e)
{
if (_featureTable.LoadStatus != Esri.ArcGISRuntime.LoadStatus.Loaded)
{
return;
}
try
{
_progressBar.Visibility = Android.Views.ViewStates.Visible;
// 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 AlertDialog.Builder(this).SetMessage($"Query returned {result.Count()} features.").SetTitle("Query Completed").SetPositiveButton("OK", (EventHandler<DialogClickEventArgs>)null).Show();
}
catch (Exception ex)
{
new AlertDialog.Builder(this).SetMessage(ex.Message).SetTitle(ex.GetType().Name).Show();
}
finally
{
// Update the UI.
_progressBar.Visibility = Android.Views.ViewStates.Gone;
}
}
private async void StartDateClick(object sender, EventArgs e)
{
try
{
// Prompt the user with the default time or currently set time.
DateTime promptDate = new DateTime(2011, 6, 13);
if (_startTime is DateTime validStart)
{
promptDate = validStart;
}
// Await the user selecting a date.
DateTime? newTime = await PromptForDate(promptDate);
if (newTime is DateTime time)
{
_startTime = time;
_startDateButton.Text = time.ToShortDateString();
}
else
{
_startTime = null;
_startDateButton.Text = "Start date";
}
}
catch (Exception)
{
}
}
private async void EndDateClick(object sender, EventArgs e)
{
try
{
// Prompt the user with the default time or currently set time.
DateTime promptDate = new DateTime(2011, 6, 13);
if (_endTime is DateTime validEnd)
{
promptDate = validEnd;
}
// Await the user selecting a date.
DateTime? newTime = await PromptForDate(promptDate);
if (newTime is DateTime time)
{
_endTime = time;
_endDateButton.Text = time.ToShortDateString();
}
else
{
_endTime = null;
_endDateButton.Text = "End date";
}
}
catch (Exception)
{
}
}
private async Task<DateTime?> PromptForDate(DateTime initialTime)
{
try
{
// Create the task completion source.
_dateTimeTCS = new TaskCompletionSource<DateTime>();
// Prompt the user for a datetime.
DatePickerDialog dialog = new DatePickerDialog(this, DatePromptCallback, initialTime.Year, initialTime.Month, initialTime.Day);
dialog.CancelEvent += (s, e) => { _dateTimeTCS.SetCanceled(); };
dialog.Show();
var result = await _dateTimeTCS.Task;
return result;
}
catch (Exception)
{
return null;
}
}
private void DatePromptCallback(object sender, DatePickerDialog.DateSetEventArgs e)
{
try
{
// Set the result of the task completion source using the date the user selected via the control.
_dateTimeTCS.SetResult(e.Date);
}
catch (Exception)
{
_dateTimeTCS.TrySetCanceled();
}
}
private void DateSwitchChanged(object sender, CompoundButton.CheckedChangeEventArgs e)
{
_startDateButton.Enabled = _endDateButton.Enabled = e.IsChecked;
}
}
}