Display and Edit Simple Type Values in a Lookup Property Editor

• Apr 18, 2022
• 8 minutes to read

This help topic describes how to allow end users to select a property value of a simple type (string, integer, enumeration, and so on) in a lookup editor.

Important

The examples demonstrated in this help topic require calculation on the client side and do not support Server, ServerView, InstantFeedback, and InstantFeedbackView modes.

Populate the Lookup Editor with Values from Another Property

This section demonstrates how to display user-friendly strings instead of simple type values in a lookup editor.

Scenario

Suppose you have the following class and want to display user-friendly strings for the Position integer property:

File: MySolution.Module\BusinessObjects\DemoClass.cs(.vb).

C#

using DevExpress.Persistent.Base;
using DevExpress.Persistent.BaseImpl;
using DevExpress.Xpo;
//...
[DefaultClassOptions]
public class DemoClass : BaseObject {
    public DemoClass(Session session) : base(session) { }
    int _position;
    public int Position {
        get { return _position; }
        set { SetPropertyValue(nameof(Position), ref _position, value); }
    }
}

VB.NET

Imports DevExpress.Persistent.Base
Imports DevExpress.Persistent.BaseImpl
Imports DevExpress.Xpo
'...
<DefaultClassOptions>
Public Class DemoClass
    Inherits BaseObject
    Public Sub New(ByVal session As Session)
        MyBase.New(session)
    End Sub
    Private _position As Integer
    Public Property Position() As Integer
        Get
            Return _position
        End Get
        Set(ByVal value As Integer)
            SetPropertyValue(NameOf(Position), _position, value)
        End Set
    End Property
End Class

The UI with a numeric editor (before customization)

The UI with a lookup editor (after customization)

Solution

1. Apply the Browsable attribute to the Position property to hide its editor from the UI:

   C#

   using System.ComponentModel;
   //...
   public class DemoClass {
       //...
       [Browsable(false)]
       public int Position {
           //...
       }
   }
   

   VB.NET

   Imports System.ComponentModel
   '...
   Public Class DemoClass
       '...
       <Browsable(False)>
       Public Property Position As Integer
           '...
       End Property
   End Class
   

2. Create an additional PositionPropertyWrapper class that is a wrapper for the DemoClass.Position property. Apply the DomainComponent attribute to this class to make it non-persistent. In PositionPropertyWrapper, the Key property stores the original integer values, and the DisplayName property returns their user-friendly string representations.

   File: MySolution.Module\BusinessObjects\PositionPropertyWrapper.cs(.vb).

   C#

   using DevExpress.ExpressApp.DC;
   //...
   [DomainComponent, XafDefaultProperty(nameof(PositionName))]
   public class PositionPropertyWrapper {
       private int _key;
       private string _positionName;
       public PositionPropertyWrapper(string positionName, int key) {
           this._key = key;
           this._positionName = positionName;
       }
       [DevExpress.ExpressApp.Data.Key]
       public int Key { get { return _key; } }
       public string PositionName { get { return _positionName; } }
   }
   

   VB.NET

   Imports DevExpress.ExpressApp.DC
   '...
   <DomainComponent, XafDefaultProperty(nameof(PositionName))>
   Public Class PositionPropertyWrapper
       Private _key As Integer
       Private _positionName As String
       Public Sub New(ByVal positionName As String, ByVal key As Integer)
           Me._key = key
           Me._positionName = positionName
       End Sub
       <DevExpress.ExpressApp.Data.Key>
       Public ReadOnly Property Key() As Integer
           Get
               Return _key
           End Get
       End Property
       Public ReadOnly Property PositionName() As String
           Get
               Return _positionName
           End Get
       End Property
   End Class
   

   Important

   Use the Key attribute from the DevExpress.ExpressApp.Data namespace only (not from the System.ComponentModel.DataAnnotations or DevExpress.Xpo namespaces). This attribute is required for XAF ASP.NET Web Forms and ASP.NET Core Blazor applications.

3. Extend DemoClass with the PositionDataSource property that stores the collection of non-persistent PositionPropertyWrapper objects. The Position lookup editor displays these objects. Apply the Browsable attribute to the PositionDataSource property to hide its editor from the UI:

   File: MySolution.Module\BusinessObjects\DemoClass.cs(.vb).

   C#

   using System.ComponentModel;
   //...
   public class DemoClass {
       //...
       private BindingList<PositionPropertyWrapper> _positionDataSource;
       [Browsable(false)]
       public BindingList<PositionPropertyWrapper> PositionDataSource {
           get {
               if (_positionDataSource == null) {
                   _positionDataSource = new BindingList<PositionPropertyWrapper>();
                   for (int i = 0; i < 5; i++) {
                       _positionDataSource.Add(new PositionPropertyWrapper("Position" + i.ToString(), i));
                   }
               }
               return _positionDataSource;
           }
       }
   }
   

   VB.NET

   Imports System.ComponentModel
   '...
   Public Class DemoClass
       '...
       Private dataSource As BindingList(Of PositionPropertyWrapper)
       <Browsable(False)>
       Public ReadOnly Property PositionsDataSource() As BindingList(Of PositionPropertyWrapper)
           Get
               If dataSource Is Nothing Then
                   dataSource = New BindingList(Of PositionPropertyWrapper)()
                   For i As Integer = 0 To 4
                       dataSource.Add(New PositionPropertyWrapper("Position" & i.ToString(), i))
                   Next i
               End If
               Return dataSource
           End Get
       End Property
   End Class
   

4. Extend DemoClass with the non-persistent PositionWrapper property of the PositionPropertyWrapper type to update the persistent Position property. Apply the DataSourceProperty attribute to PositionWrapper to populate the lookup editor data source:

   C#

   using System.Linq;
   // ...
   public class DemoClass {
       // ...
       private PositionPropertyWrapper _positionPropertyWrapper;
       [NonPersistent, XafDisplayName("Position")]
       [DataSourceProperty(nameof(PositionDataSource))]
       public PositionPropertyWrapper PositionWrapper {
           get {
               if (_positionPropertyWrapper == null || _positionPropertyWrapper.Key != Position) {
                   _positionPropertyWrapper = PositionDataSource.FirstOrDefault(i => i.Key == Position);
               }
               return _positionPropertyWrapper;
           }
           set {
               SetPropertyValue(nameof(PositionWrapper), ref _positionPropertyWrapper, value);
               if (!IsLoading && !IsSaving) {
                   Position = value.Key;
               }
           }
       }
   }
   

   VB.NET

   Imports System.Linq
   ' ...
   Public Class DemoClass
       ' ...
       Private _positionPropertyWrapper As PositionPropertyWrapper
       <NonPersistent, XafDisplayName("Position"), DataSourceProperty(nameof(PositionDataSource))>
       Public Property PositionWrapper() As PositionPropertyWrapper
           Get
               If _positionPropertyWrapper Is Nothing OrElse _positionPropertyWrapper.Key <> Position Then
                   _positionPropertyWrapper = PositionDataSource.FirstOrDefault(Function(i) i.Key = Position)
               End If
               Return _positionPropertyWrapper
           End Get
           Set(ByVal value As PositionPropertyWrapper)
               SetPropertyValue(NameOf(PositionWrapper), _positionPropertyWrapper, value)
               If Not IsLoading AndAlso Not IsSaving Then
                   Position = value.Key
               End If
           End Set
       End Property
   End Class
   

5. Optional. You can also hide the lookup editor’s Clear button for a non-nullable PositionWrapper property. To do this, set its AllowClear property to false in the Model Editor or apply ModelDefaultAttribute to PositionWrapper:

   C#

   using DevExpress.ExpressApp.Model;
   // ...
   public class DemoClass {
       // ...
       [ModelDefault("AllowClear", "false")]
       public PositionPropertyWrapper PositionWrapper {
           // ...
       }
   }
   

   VB.NET

   Imports DevExpress.ExpressApp.Model
   ' ...
   Public Class DemoClass
       ' ...
       <ModelDefault("AllowClear", "false")>
       Public Property PositionWrapper() As PositionPropertyWrapper
           ' ...
       End Property
   End Class
   

Populate the Lookup Editor with Persistent Business Objects

This section demonstrates how to display a lookup editor with persistent objects instead of a simple type editor. Use this technique if you have legacy databases and cannot modify their schemas to create associations between tables.

Scenario

Suppose you have the following classes and want to display the Position.Title lookup editor instead of the DemoClass.PositionTitle string editor.

C#

using DevExpress.ExpressApp.DC;
using DevExpress.Persistent.Base;
using DevExpress.Persistent.BaseImpl;
using DevExpress.Xpo;
//...
[DefaultClassOptions]
public class DemoClass : BaseObject {
    public DemoClass(Session session) : base(session) { }
    string positionTitle;
    public string PositionTitle {
        get { return positionTitle; }
        set { SetPropertyValue(nameof(PositionTitle), ref positionTitle, value); }
    }
}

[DefaultClassOptions, XafDefaultProperty(nameof(Title))]
public class Position : BaseObject {
    public Position(Session session) : base(session) { }
    string _title;
    [Size(SizeAttribute.DefaultStringMappingFieldSize)]
    public string Title {
        get {
            return _title;
        }
        set {
            SetPropertyValue(nameof(Title), ref _title, value);
        }
    }
}

VB.NET

Imports DevExpress.ExpressApp.DC
Imports DevExpress.Persistent.Base
Imports DevExpress.Persistent.BaseImpl
Imports DevExpress.Xpo
'...
<DefaultClassOptions>
Public Class DemoClass
    Inherits BaseObject
    Public Sub New(ByVal session As Session)
        MyBase.New(session)
    End Sub
    Private _positionTitle As String
    Public Property PositionTitle As String
        Get
            Return _positionTitle
        End Get
        Set(ByVal value As String)
            SetPropertyValue(NameOf(PositionTitle), _positionTitle, value)
        End Set
    End Property
End Class

<DefaultClassOptions, XafDefaultProperty(NameOf(Position.Title))>
Public Class Position
    Inherits BaseObject
    Public Sub New(ByVal session As Session)
        MyBase.New(session)
    End Sub
    Private _title As String
    <Size(SizeAttribute.DefaultStringMappingFieldSize)>
    Public Property Title As String
        Get
            Return _title
        End Get
        Set(ByVal value As String)
            SetPropertyValue(NameOf(Title), _title, value)
        End Set
    End Property
End Class

The UI with a string editor (before customization)

The UI with a lookup editor (after customization)

Solution

1. Apply the Browsable attribute to the PositionTitle property to hide its editor from the UI:

   C#

   using System.ComponentModel;
   //...
   public class DemoClass {
       //...
       [Browsable(false)]
       public string PositionTitle {
           //...
       }
   }
   

   VB.NET

   Imports System.ComponentModel
   '...
   Public Class DemoClass
       '...
       <Browsable(False)>
       Public Property PositionTitle As String
           '...
       End Property
   End Class
   

2. Create a non-persistent wrapper property (LookupPropertyForDisplay) to fetch records from the Position data table:

   C#

   using DevExpress.Data.Filtering;
   using DevExpress.ExpressApp.DC;
   using DevExpress.Xpo;
   //...
   public class DemoClass {
       //...
       private Position _LookupPropertyForDisplay;
       [NonPersistent, XafDisplayName("Position")]
       public Position LookupPropertyForDisplay {
           get {
               if ((_LookupPropertyForDisplay == null && !string.IsNullOrEmpty(positionTitle)) || 
               (_LookupPropertyForDisplay != null && _LookupPropertyForDisplay.Title != PositionTitle)) {
                   _LookupPropertyForDisplay = 
                       Session.FindObject<Position>(new BinaryOperator("Title", positionTitle));
               }
               return _LookupPropertyForDisplay;
           }
           set {
               SetPropertyValue<Position>(nameof(LookupPropertyForDisplay), 
                                          ref _LookupPropertyForDisplay, value);
               if (!IsLoading && !IsSaving) {
                   PositionTitle = value != null ? value.Title : string.Empty;
               }
           }
       }
   }
   

   VB.NET

   Imports DevExpress.Data.Filtering
   Imports DevExpress.ExpressApp.DC
   Imports DevExpress.Xpo
   '...
   Public Class DemoClass
       '...
       Private _LookupPropertyForDisplay As Position
       <NonPersistent, XafDisplayName("Position")>
       Public Property LookupPropertyForDisplay() As Position
           Get
               If (_LookupPropertyForDisplay Is Nothing AndAlso Not String.IsNullOrEmpty(positionTitle)) OrElse
               (_LookupPropertyForDisplay IsNot Nothing AndAlso _LookupPropertyForDisplay.Title <> PositionTitle) Then
                   _LookupPropertyForDisplay = 
                       Session.FindObject(Of Position)(New BinaryOperator("Title", positionTitle))
               End If
               Return _LookupPropertyForDisplay
           End Get
           Set(ByVal value As Position)
               SetPropertyValue(Of Position)(NameOf(LookupPropertyForDisplay),
                                             _LookupPropertyForDisplay, value)
               If Not IsLoading AndAlso Not IsSaving Then
                   PositionTitle = If(value IsNot Nothing, value.Title, String.Empty)
               End If
           End Set
       End Property
   End Class
   

Notes

• You can also filter the Lookup Property Editor data sources as described in the following help topic: How to: Implement Cascading Filtering for Lookup List Views.

• Refer to the following help topics for more information on other ways to implement similar tasks:

  • How to: Display an Integer Property as an Enumeration
  • How to: Implement a Property Editor Based on a Custom Control (WinForms)
  • How to: Implement a Property Editor Based on Custom Controls (ASP.NET)
  • How to: Implement a Property Editor Based on a Custom Component (Blazor)
  • How to: Supply Predefined Values for the String Property Editor Dynamically (WinForms)
  • How to: Supply Predefined Values for the String Property Editor Dynamically (ASP.NET)