BLOB Image Properties in Entity Framework

• Feb 24, 2022
• 3 minutes to read

You can declare image properties as a byte array property, or as a reference properties of the MediaDataObject type (available in the Business Class Library).

• Image as a Byte Array
• Image as a MediaDataObject

Image as a Byte Array

The example below illustrates how to implement image properties in an Entity Framework Code-First class. Declare a byte array property and apply the ImageEditorAttribute to it. Optionally, you can customize the behavior of the image editor using the attribute’s parameters.

C#

using System.Drawing;
using System.ComponentModel;
using System.ComponentModel.DataAnnotations.Schema;
// ...
[DefaultClassOptions]
public class Employee {
    // ...
    [ImageEditor(ListViewImageEditorMode = ImageEditorMode.PopupPictureEdit,
        DetailViewImageEditorMode = ImageEditorMode.DropDownPictureEdit)]
    public byte[] Photo { get; set; }
}

VB.NET

Imports System.Drawing
Imports System.ComponentModel
Imports System.ComponentModel.DataAnnotations.Schema
' ...
<DefaultClassOptions>
Public Class Employee
    ' ...

    Private _photo As Image
    ' The hidden property that is mapped to a database column
    ' and stores image data as a binary array.
    Private privatePhotoData As Byte()
    <Browsable(False)>
    Public Property PhotoData() As Byte()
        Get
            Return privatePhotoData
        End Get
        Protected Set(ByVal value As Byte())
            privatePhotoData = value
        End Set
    End Property
    ' The property that is visible in XAF UI, but is not mapped to a database column.
    <NotMapped, _
    ImageEditor(ListViewImageEditorMode := ImageEditorMode.PopupPictureEdit, _
    DetailViewImageEditorMode := ImageEditorMode.DropDownPictureEdit)>
    Public Property Photo() As Image
        Get
            If (_photo Is Nothing) AndAlso (PhotoData IsNot Nothing) Then
                Dim imageConverter As New ImageConverter()
                _photo = CType(imageConverter.ConvertFrom(PhotoData), Image)
            End If
            Return _photo
        End Get
        Set(ByVal value As Image)
            _photo = value
            If _photo Is Nothing Then
                PhotoData = Nothing
            Else
                Dim imageConverter As New ImageConverter()
                PhotoData = CType(imageConverter.ConvertTo(_photo, GetType(Byte())), Byte())
            End If
        End Set
    End Property
End Class

Refer to the ImageEditorAttribute topic for details on parameters passed to the ImageEditor attribute in the code above. You can also specify image options using the following properties in the Model Editor:

• IModelCommonMemberViewItem.ImageSizeMode
• IModelMember.DetailViewImageEditorMode
• IModelMember.DetailViewImageEditorFixedWidth
• IModelMember.DetailViewImageEditorFixedHeight
• IModelMember.ListViewImageEditorMode
• IModelMember.ListViewImageEditorCustomHeight

Tip

When an application displays a lot of large images in a List View, it may consume a lot of memory. It is most true for ASP.NET applications with many simultaneously connected clients. To improve the performance, you can use lazy loading, as demonstrated in the How to enable delayed loading of images in Entity Framework example.

Image as a MediaDataObject

The example below illustrates how to implement image properties of the MediaDataObject type (available in the Business Class Library) in an Entity Framework Code-First class. Both WinForms and ASP.NET Image Property Editors are used automatically for properties of the MediaDataObjecttype, no attributes are required (however, you still can apply the ImageEditorAttribute to customize the editor’s options, as it is demonstated above for byte arrays). The use of this type reduces traffic because images are cached in the browser cache (compared to images of the byte[] type). The delayed loading is always used for MediaDataObjectproperties.

C#

using DevExpress.ExpressApp;
using DevExpress.Persistent.Base;
using DevExpress.Persistent.BaseImpl.EF;
// ...
[DefaultClassOptions]
public class Contact {
    [Browsable(false)]
    public int ID { get; private set; }
    public string Name { get; set; }
    public virtual MediaDataObject Photo { get; set; }
}

VB.NET

Imports DevExpress.ExpressApp
Imports DevExpress.Persistent.Base
Imports DevExpress.Persistent.BaseImpl.EF
' ...
<DefaultClassOptions> _
Public Class Contact
    Private privateID As Integer
    <Browsable(False)> _
    Public Property ID() As Integer
        Get
            Return privateID
        End Get
        Private Set(ByVal value As Integer)
            privateID = value
        End Set
    End Property
    Public Property Name() As String
    Public Overridable Property Photo() As MediaDataObject
End Class