JavaScript/jQuery TreeList - columns.lookup

A lookup column restricts the set of values that can be chosen when a user edits or filters the column. In a lookup column, each cell is a drop-down menu. You can use a lookup column when you need to substitute displayed values with required values. For example, consider that you have two arrays of objects: drivers and buses.

var drivers = [
    { driverID: 1, firstName: "John", lastName: "Smith", busID: 2 },
    { driverID: 2, firstName: "Lizzy", lastName: "Cook", busID: 1 },
    { driverID: 3, firstName: "Brian", lastName: "Hawkins", busID: 3 }
];

var buses = [
    { busID: 1, plates: "123456" },
    { busID: 2, plates: "AB-1234" },
    { busID: 3, plates: "CD-9876" }
];

All drivers have the busID field, which refers to a bus. If drivers is the main dataSource, the Bus ID column displays bus IDs, which provides little information to a user. It will be more useful to display bus license plates instead of IDs. For this, the buses array must be set as a lookup dataSource for the Bus ID column. Then, the names of data fields must be assigned to the valueExpr and displayExpr options. Values from the valueExpr data field will be replaced with values from the displayExpr data field.

$(function() {
    $("#treeListContainer").dxTreeList({
        dataSource: drivers,
        // ...
        columns: [{
            dataField: "busID",
            lookup: {
                dataSource: buses,
                valueExpr: "busID",
                displayExpr: "plates"
            }
        }]
    });
});

<dx-tree-list [dataSource]="drivers">
    <dxi-column dataField="busID">
        <dxo-lookup
            [dataSource]="buses"
            valueExpr="busID"
            displayExpr="plates">
        </dxo-lookup>
    </dxi-column>
</dx-tree-list>

import { DxTreeListModule } from "devextreme-angular";
// ...
export class AppComponent {
    drivers = [
        { driverID: 1, firstName: "John", lastName: "Smith", busID: 2 },
        { driverID: 2, firstName: "Lizzy", lastName: "Cook", busID: 1 },
        { driverID: 3, firstName: "Brian", lastName: "Hawkins", busID: 3 }
    ];
    buses = [
        { busID: 1, plates: "123456" },
        { busID: 2, plates: "AB-1234" },
        { busID: 3, plates: "CD-9876" }
    ];
}
@NgModule({
    imports: [
        // ...
        DxTreeListModule
    ],
    // ...
})

With this code, the Bus ID column contains license plates instead of IDs. Moreover, the user can choose a plate number from the drop-down menu when editing cells or applying a filter to this column.

See Also

• Bind a Lookup Column to a Custom Data Source
• Customize Editors

Set this option to true only if your data source accepts null values.

To specify this option based on a condition, set the showClearButton option instead. This is an option of the SelectBox widget which is used as an editor for lookup column cells. allowClearing is an alias for this option in the TreeList. The following code shows how to set showClearButton in the onEditorPreparing event handler:

$(function() {
    $("#treeListContainer").dxTreeList({
        // ...
        onEditorPreparing: function (e) {
            if (/* a condition to set the option's value */) {
                e.editorOptions.showClearButton = true;
            }
        }
    });
});

import { Component } from '@angular/core';

@Component({
    selector: 'app-root',
    templateUrl: './app.component.html',
    styleUrls: ['./app.component.css']
})
export class AppComponent {
    onEditorPreparing(e) {
        if (/* a condition to set the option's value */) {
            e.editorOptions.showClearButton = true;
        }
    }
}

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { AppComponent } from './app.component';

import { DxTreeListModule } from 'devextreme-angular';

@NgModule({
    declarations: [
        AppComponent
    ],
    imports: [
        BrowserModule,
        DxTreeListModule
    ],
    bootstrap: [AppComponent]
})
export class AppModule { }

<dx-tree-list ...
    (onEditorPreparing)="onEditorPreparing($event)">
    <!-- ... -->
</dx-tree-list>

<template>
    <DxTreeList ...
        :on-editor-preparing="onEditorPreparing">
        <!-- ... -->
    </DxTreeList>
</template>

<script>
import 'devextreme/dist/css/dx.common.css';
import 'devextreme/dist/css/dx.light.css';

import DxTreeList from 'devextreme-vue/tree-list';

export default {
    components: {
        DxTreeList
    },
    // ...
    methods: {
        onEditorPreparing(e) {
            if (/* a condition to set the option's value */) {
                e.editorOptions.showClearButton = true;
            }
        }
    }
}
</script>

import React from 'react';

import 'devextreme/dist/css/dx.common.css';
import 'devextreme/dist/css/dx.light.css';

import TreeList from 'devextreme-react/tree-list';

class App extends React.Component {
    onEditorPreparing(e) {
        if (/* a condition to set the option's value */) {
            e.editorOptions.showClearButton = true;
        }
    }

    render() {
        return (
            <TreeList ...
                onEditorPreparing={this.onEditorPreparing}>
                {/* ... */}
            </TreeList>
        );
    }
}
export default App;

This option accepts one of the following:

• Array of objects or primitives
  A JavaScript array that contains plain objects or primitives.

• DataSource configuration object
  A DataSource configuration object. For more information about the DataSource and DevExtreme Data Layer, refer to the Data Layer article.

  IMPORTANT

  DataSource instances are not supported.

• Store instance
  An ArrayStore, LocalStore, ODataStore, or CustomStore instance.

• Function
  A function that returns one of the above.

If the lookup data source contains objects, specify the valueExpr and displayExpr options in addition to the dataSource.

View Demo

See Also

• How to: Bind a Lookup Column to a Custom Data Source

This option accepts a string - the name of the data field that provides displayed values, or a function that returns the displayed value.

columns: [{
    // ...
    lookup: {
        // ...
    },
    calculateSortValue: function (data) {
        var value = this.calculateCellValue(data);
        return this.lookup.calculateCellValue(value);
    }
}]

<dxi-column
    ...
    [calculateSortValue]="calculateSortValue">
    <dxo-lookup ... ></dxo-lookup>
</dxi-column>

export class AppComponent {
    calculateSortValue (data) {
        let column = this as any;
        let value = column.calculateCellValue(data);
        return column.lookup.calculateCellValue(value);
    }
}

Values from this field will be replaced with values from the displayExpr field.