Feature layer definition expression

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Sample viewer app

Limit the features displayed on a map with a definition expression.

screenshot

Use case

Set a definition expression to filter out the features to be displayed. You might filter a dataset of tree quality selecting for only those trees which require maintenance or are damaged.

How to use the sample

Press 'Apply Expression' to limit the features requested from the feature layer to those specified by the SQL query definition expression. Click 'Reset Expression' to remove the definition expression on the feature layer, which returns all the records.

How it works

  1. Create a service feature table from a URL.
  2. Create a feature layer from the service feature table.
  3. Set the limit of the features on your feature layer using the DefinitionExpression.

Relevant API

  • DefinitionExpression
  • FeatureLayer
  • ServiceFeatureTable

About the data

This map displays point features related to crime incidents that have been reported by city residents.

Tags

definition expression, filter, limit data, query, restrict data, SQL, where clause

Sample Code

FeatureLayerDefinitionExpression.qmlFeatureLayerDefinitionExpression.cppFeatureLayerDefinitionExpression.h
                                                                   
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// [WriteFile Name=FeatureLayerDefinitionExpression, Category=Features]
// [Legal]
// Copyright 2016 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.
// [Legal]

import QtQuick 2.6
import QtQuick.Controls 2.2
//! [Import the namespace that has QML type that was registered in Cpp]
import Esri.Samples 1.0
//! [Import the namespace that has QML type that was registered in Cpp]

FeatureLayerDefinitionExpressionSample {
    id: definitionExpressionSample
    width: 800
    height: 600

    //! [Declare map view in QML that will be accessed from Cpp]
    // add a mapView component
    MapView {
        anchors.fill: parent
        objectName: "mapView"
    }
    //! [Declare map view in QML that will be accessed from Cpp]

    Row {
        id: expressionRow
        anchors {
            bottom: parent.bottom
            left: parent.left
            right: parent.right
            margins: 5
            bottomMargin: 25
        }
        spacing: 5

        // button to apply a definition expression
        Button {
            text: "Apply Expression"
            enabled: definitionExpressionSample.layerInitialized
            onClicked: {
                // Call C++ invokable function to set the definition expression
                definitionExpressionSample.setDefExpression("req_Type = \'Tree Maintenance or Damage\'");
            }
        }

        // button to reset the definition expression
        Button {
            text: "Reset"
            enabled: definitionExpressionSample.layerInitialized
            onClicked: {
                // Call C++ invokable function to reset the definition expression
                definitionExpressionSample.setDefExpression("");
            }
        }
    }
}

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