XAF : How to access HttpSessionState anywhere in the XAF Project

You can access it by HttpContext.Current.Session(0)

XAF : Display Collection Properties in an Edit Mode Detail View for an ASP.NET Application

To display collection properties when we have 1-M relation between two classes 'ClassA' and 'ClassB':

1. Override 'OnLoggingOn' Sub in 'WebApplication.vb'
2. add this statement to the sub
   CType(MyBase.ShowViewStrategy, ShowViewStrategy).CollectionsEditMode = DevExpress.ExpressApp.Editors.ViewEditMode.Edit

---

Collection properties will be displayed in both the View and Edit modes. Collection properties will be editable in Edit mode and read-only in View mode:

XAF : Set PredefinedValues from the code

1. Create fake values for predefinedvalues using application model
   
   
2. Create XAF view controller. i.e. PredefinedValuesController
3. make it inherit from DevExpress.ExpressApp.ViewController(Of DetailView)
4. override method Protected Overrides Sub OnActivated()
5. Read PropertyEditor for required attribute.
   i.e. Dim editor As ASPxStringPropertyEditor = TryCast(View.FindItem(AttributeName), ASPxStringPropertyEditor)
6. then, add the values to the editor
   - Dim control As ASPxComboBox = TryCast(editor, ASPxComboBox)
   -         If control IsNot Nothing Then
   -            AddHandler control.Load, Sub(s, e)
   -            control.Items.Clear()
   -            control.Items.Add("item 1")
   -            control.Items.Add("item 2")
   -       End Sub
   -       End If

Full Example:

- 'MobileDevice' is the name of buisness object

- GetPredefinedValues is an SqlServer Procedure that gets all distinct values for a business object attribute.

  in our example business object is 'MobileDevice' and the attribute is 'IMEI'

CREATE PROCEDURE [dbo].[GetPredefinedValues]

    -- Add the parameters for the stored procedure here

    @tbl nvarchar(200)

    , @col nvarchar(200)

AS

BEGIN

    declare @sql nvarchar(400)

    set @sql = 'SELECT DISTINCT '+@col+' FROM '+@tbl+' WHERE '+@col+' IS NOT NULL ORDER BY '+@col

    -- SET NOCOUNT ON added to prevent extra result sets from

    -- interfering with SELECT statements.

    print @sql

exec     sp_executesql @sql

    SET NOCOUNT ON;

    -- Insert statements for procedure here

END

   1:  Imports System

   2:  Imports System.ComponentModel

   3:  Imports System.Collections.Generic

   4:  Imports System.Diagnostics

   5:  Imports System.Text

   6:   

   7:  Imports DevExpress.ExpressApp

   8:  Imports DevExpress.ExpressApp.Actions

   9:  Imports DevExpress.Persistent.Base

  10:  Imports DevExpress.ExpressApp.Web.Editors.ASPx

  11:  Imports DevExpress.Web.ASPxEditors

  12:  Imports DevExpress.Persistent.BaseImpl

  13:  Imports DevExpress.Xpo

  14:  Imports DevExpress.Data.Filtering

  15:  Imports BillingSystem.Module.Devices

  16:   

  17:  Public Class PredefinedValuesController

  18:      Inherits DevExpress.ExpressApp.ViewController(Of DetailView)

  19:   

  20:      Public Sub New()

  21:          MyBase.New()

  22:   

  23:          'This call is required by the Component Designer.

  24:          InitializeComponent()

  25:          RegisterActions(components)

  26:   

  27:      End Sub

  28:   

  29:     

  30:   

  31:      Protected Overrides Sub OnActivated()

  32:          MyBase.OnActivated()

  33:          ' to add for more values we

  34:          If TypeOf View.CurrentObject Is MobileDevice Then

  35:              SetPreDefinedValues("MobileDevice", "IMEI")

  36:   

  37:          End If

  38:   

  39:      End Sub

  40:    

  41:      Private Sub SetPreDefinedValues(ByVal tableName As String, ByVal columnName As String)

  42:          Dim editor As ASPxStringPropertyEditor = TryCast(View.FindItem(columnName), ASPxStringPropertyEditor)

  43:          If editor IsNot Nothing AndAlso View.ViewEditMode = DevExpress.ExpressApp.Editors.ViewEditMode.Edit Then

  44:              If editor.Control IsNot Nothing Then

  45:                  Customize(editor.Editor, tableName, columnName)

  46:              Else

  47:                  AddHandler editor.ControlCreated, Sub(s, e) Customize(editor.Editor, tableName, columnName)

  48:              End If

  49:          End If

  50:      End Sub

  51:   

  52:      Private Sub Customize(ByVal p As Object, ByVal tableName As String, ByVal columnName As String)

  53:          Dim control As ASPxComboBox = TryCast(p, ASPxComboBox)

  54:          If control IsNot Nothing Then

  55:              AddHandler control.Load, Sub(s, e)

  56:                                           control.Items.Clear()

  57:                                           For Each item As String In GetPredefinedValuesFromTableColumn(tableName, columnName)

  58:                                               control.Items.Add(item)

  59:                                           Next

  60:                                       End Sub

  61:          End If

  62:      End Sub

  63:      Private Function GetPredefinedValuesFromTableColumn(ByVal tableName As String, ByVal columnName As String) As List(Of String)

  64:          Dim paramsOperand As New List(Of OperandValue)

  65:          paramsOperand.AddRange(New OperandValue() {tableName, columnName})

  66:          Dim session As Session = CType(SecuritySystem.CurrentUser, User).Session

  67:          Dim res As DB.SelectedData = session.ExecuteSproc("GetPredefinedValues", paramsOperand.ToArray)

  68:          Dim result As New List(Of String)

  69:          For Each row As DB.SelectStatementResultRow In res.ResultSet(0).Rows

  70:              result.Add(row.Values(0).ToString())

  71:          Next

  72:          Return result

  73:   

  74:      End Function

  75:   

  76:   

  77:  End Class

XAF : Remove HyperLinks between objects

• Create custom property by descend from the ASPxLookupPropertyEditor class
• decide class object in which this custom property will use for.
• override ShowLink property and make it return value of '0' as below example

Imports DevExpress.ExpressApp.Web.Editors.ASPx
Imports DevExpress.ExpressApp.Model
<DevExpress.ExpressApp.Editors.PropertyEditor(GetType(YourBusinessClass), False)> _
Public Class CustomASPxLookupPropertyEditor
    Inherits ASPxLookupPropertyEditor
    Public Sub New(ByVal objectType As Type, ByVal info As IModelMemberViewItem)
        MyBase.New(objectType, info)
    End Sub
    Protected Overrides Function CanShowLink() As Boolean
        Return False ' MyBase.CanShowLink()
    End Function
End Class

XAF : Access current object when override Link or UnLink actions

To do this, follow the following steps

1. Create XAF ViewController that inherit from WebLinkUnlinkController Class
2. Override Link or Unlink actions
   Protected Overrides Sub Link(ByVal args As DevExpress.ExpressApp.Actions.PopupWindowShowActionExecuteEventArgs)
3. Use the following code to access the current object
   CType(Frame, NestedFrame).ViewItem.CurrentObject

Code:

   1:  Imports System

   2:  Imports System.ComponentModel

   3:  Imports System.Collections.Generic

   4:  Imports System.Diagnostics

   5:  Imports System.Text

   6:   

   7:  Imports DevExpress.ExpressApp

   8:  Imports DevExpress.ExpressApp.Actions

   9:  Imports DevExpress.Persistent.Base

  10:  Imports DevExpress.ExpressApp.SystemModule

  11:  Imports DevExpress.Persistent.BaseImpl

  12:  Imports DevExpress.Data.Filtering

  13:  Imports DevExpress.ExpressApp.Web.SystemModule

  14:   

  15:  Public Class CustomLinkUnlinkViewController

  16:      Inherits WebLinkUnlinkController

  17:   

  18:      Public Sub New()

  19:          MyBase.New()

  20:   

  21:          'This call is required by the Component Designer.

  22:          InitializeComponent()

  23:          RegisterActions(components)

  24:   

  25:      End Sub

  26:   

  27:      Protected Overrides Sub OnActivated()

  28:          'Dim target As LinkUnlinkController = Frame.GetController(Of LinkUnlinkController)()

  29:          ' target.LinkAction.Active.SetItemValue("LinkAction", False)

  30:          ' target.UnlinkAction.Active.SetItemValue("UnlinkAction", False)

  31:          'InputBox("", "", View.Id)

  32:          MyBase.OnActivated()

  33:      End Sub

  34:   

  35:      Protected Overrides Sub Link(ByVal args As DevExpress.ExpressApp.Actions.PopupWindowShowActionExecuteEventArgs)

  36:          MyBase.Link(args)

  37:   

  38:      End Sub

  39:   

  40:   

  41:   

  42:  End Class

XAF : Execute SQL Procedure within Controller

Simply you can access session object via current user object, then you'll have full access to all functions in this object. To do this:

1. Dim session As Session = CType(SecuritySystem.CurrentUser, User).Session
2. session.ExecuteSproc("YourSqlProcedure").

another example:

1. Dim paramsOperand As New List(Of OperandValue)
2. Dim session As Session = CType(SecuritySystem.CurrentUser, User).Session
3. Dim curUserOid As Guid = CType(SecuritySystem.CurrentUser, User).Oid
4. paramsOperand.AddRange(New OperandValue() {curUserOid})
5. session.ExecuteSproc("TransferThisPeriodBills", paramsOperand.ToArray)

XAF : Grouping of Report Data Based on Specific Field

To group report data based on specific field, you should follow the following steps

• Run XAF desktop application [note that report can't be modified from XAF web app.]
• Edit your report via XAF Report Designer

• Right mouse click then put mouse on Insert Band, after that click on GroupHeader.

XAF : Change Listview Default GroupSummary

The following steps will used to change group summary for Listview:

1. Open model designer by click on application file Model.xafml under YourProject.Web
    
2. Change GroupSummary Property as shown below:
   
    
3. GroupSummary Format Structure {1}:{2},{3}:{4}
   example : TotalPrivateCharge:Sum,TotalPrivateCharge:Sum={0:n2}
    
1. Property Name
2. Aggregation Function
3. Property Name
4. Aggregation String Format. [Sum={0:n2}]
1. '0' means first argument which is TotalPrivateCharge
2. 'n2' means the second argument which is aggregation function value.
5. Result for this aggregation function is 'Sum=25.12'

XAF : Add Sequence (Serial) Number into a Report

In order to add sequence or serial number such that 1,2,3,4,...etc into a report in devexpress, you should follow the following steps

• add a Label into a report

•  Expand Label Tasks dialog

•  Set Summary Function to Record Number, and Summary Running to Group

XAF : Show Reports for Individual Views

The Reports module allows you to design reports for a filtered data source. In some scenarios, you may need to preview a report for a certain object or a set of objects that are not related by a criteria. For example, the Invoice business object(s) should be able to be printed in a specific manner. In this case, a specially designed report should be available for display for a particular set of Invoice objects. For this purpose, use the Inplace Reporting feature provided by the Reports module. This topic demonstrates how to use this feature.

To show selected object(s) in a specified report, the Reports module introduces the ShowInReport Action. This Action represents the SingleChoiceAction class instance. Its items represent so-called inplace reports that are designed for the current View's object type.

XAF : Override ListView Default Action

In order to override list view default action, you should do the following

1. Add view controller to your project [i.e. ListViewActionsController]
2. make class (ListViewActionsController) inherit from DevExpress.ExpressApp.SystemModule.ListViewProcessCurrentObjectController
3. Override the function.[i.e. ProcessCurrentObject].

The following example present an example for this:

   1:  Imports System

   2:  Imports System.ComponentModel

   3:  Imports System.Collections.Generic

   4:  Imports System.Diagnostics

   5:  Imports System.Text

   6:   

   7:  Imports DevExpress.ExpressApp

   8:  Imports DevExpress.ExpressApp.Actions

   9:  Imports DevExpress.Persistent.Base

  10:   

  11:  Public Class ListViewActionsController Inherits

  12:  DevExpress.ExpressApp.SystemModule.ListViewProcessCurrentObjectController

  13:   

  14:      Public Shared usrname As String

  15:      Public Sub New()

  16:          MyBase.New()

  17:   

  18:          'This call is required by the Component Designer.

  19:          InitializeComponent()

  20:          RegisterActions(components)

  21:   

  22:      End Sub

  23:   

  24:      Protected Overrides Sub ProcessCurrentObject(ByVal e As 
               DevExpress.ExpressApp.Actions.SimpleActionExecuteEventArgs)

  25:          If (e.CurrentObject.GetType.Name = "PhoneHolder" And 
                       View.Id = "CustomHolderListView") Then        

  26:              BillingSystem.Module.sharedMod.currentClickedUsername = 
                                   CType(e.CurrentObject, PhoneHolder).UserName

  27:          End If

  28:   

  29:          MyBase.ProcessCurrentObject(e)

  30:      End Sub

  31:   

  32:  End Class

XAF : Override DetailedView Action

In order to override detailed view action such as SaveAndClose, you should do the following

1. Add view controller to your project [i.e. DefaultDetailViewActions]
2. make class (DefaultDetailViewActions) inherit from WebDetailViewController
3. Override the function.[i.e. SaveAndClose].

The following example present an example for override SaveAndClose function:

   1:  Imports System

   2:  Imports System.ComponentModel

   3:  Imports System.Collections.Generic

   4:  Imports System.Diagnostics

   5:  Imports System.Text

   6:   

   7:  Imports DevExpress.ExpressApp

   8:  Imports DevExpress.ExpressApp.Actions

   9:  Imports DevExpress.Persistent.Base

  10:   

  11:  Imports DevExpress.ExpressApp.Web.SystemModule

  12:  Public Class DefaultDetailViewActions

  13:      Inherits WebDetailViewController

  14:   

  15:      Public Sub New()

  16:          MyBase.New()

  17:   

  18:          'This call is required by the Component Designer.

  19:          InitializeComponent()

  20:          RegisterActions(components)

  21:   

  22:      End Sub

  23:   

  24:      Protected Overrides Sub SaveAndClose(ByVal args As 
                        DevExpress.ExpressApp.Actions.SimpleActionExecuteEventArgs)

  25:          If args.CurrentObject.GetType.Name = "Calendar" Then

  26:              autoCalendarEntriesAddition(args)

  27:   

  28:          End If

  29:          MyBase.SaveAndClose(args)

  30:      End Sub

XAF : Replace Dropdown Listbox PropertyEditor With RadioGroup PropertyEditor

In order to change the default property editor from which is DropdownList control to RadioGroup control, first you should add the following file to your project folders [i.e. RadioGroupEnumPropertyEditor.vb]

   1:  Imports System

   2:  Imports System.Collections.Generic

   3:  Imports DevExpress.ExpressApp.Web.Editors

   4:  Imports System.Web.UI.WebControls

   5:  Imports DevExpress.ExpressApp.Utils

   6:  Imports DevExpress.ExpressApp

   7:  Imports DevExpress.ExpressApp.Model

   8:  Imports DevExpress.Web.ASPxEditors

   9:   

  10:  Imports System.ComponentModel

  11:   

  12:  Imports DevExpress.Xpo

  13:  Imports DevExpress.Data.Filtering

  14:   

  15:  Imports DevExpress.Persistent.Base

  16:  Imports DevExpress.Persistent.BaseImpl

  17:  Imports DevExpress.Persistent.Validation

  18:   

  19:  Imports DevExpress.ExpressApp.Editors

  20:   

  21:  <PropertyEditor(GetType(RadioButton), "CustomComboEditor", False)> _

  22:  Public Class CheckboxEnumPropertyEditor

  23:      Inherits WebPropertyEditor

  24:   

  25:      Private enumDescriptor As EnumDescriptor

  26:      Private controlsHash As New Dictionary(Of ASPxRadioButton, Object)()

  27:   

  28:      Public Sub New(ByVal objectType As Type, ByVal info As IModelMemberViewItem)

  29:          MyBase.New(objectType, info)

  30:          Me.enumDescriptor = New EnumDescriptor(MemberInfo.MemberType)

  31:   

  32:      End Sub

  33:   

  34:      Protected Overrides Function CreateEditModeControlCore() As WebControl

  35:          Dim placeHolder As New Panel()

  36:          controlsHash.Clear()

  37:          For Each enumValue As Object In enumDescriptor.Values

  38:              Dim radioButton As New ASPxRadioButton()            

  39:              radioButton.ID = "radioButton_" + enumValue.ToString()

  40:              controlsHash.Add(radioButton, enumValue)

  41:              radioButton.Text = enumDescriptor.GetCaption(enumValue)

  42:              'radioButton.CheckedChanged += New EventHandler(radioButton_CheckedChanged)

  43:              AddHandler radioButton.CheckedChanged, AddressOf radioButton_CheckedChanged

  44:              radioButton.GroupName = PropertyName

  45:              placeHolder.Controls.Add(radioButton)

  46:   

XAF : Implement One-to-One Relationships

Let's consider a simple example of a One-to-One relationship, when both classes that participate in the relationship have properties with a reference to the instance of their opposite class. It's necessary to write extra code within the property's setter method for each class that participates in the relationship to ensure the relationship's integrity, i.e. when a new object is assigned to a reference property, the reference to the previous object instance should be cleared and the assigned object should reference the current one.

This technique can be implemented as shown in the following code example.

   1:  ' Represents the Building class which refers to the building's owner. 

   2:  Public Class Building : Inherits XPObject

   3:      Dim _owner As Person = Nothing 

   4:      Public Property Owner() As Person

   5:          Get 

   6:              Return _owner

   7:          End Get 

   8:          Set(ByVal Value As Person)

   9:              If _owner Is Value Then 

  10:                  Return 

  11:              End If 

  12:   

  13:              ' Store a reference to the former owner. 

  14:              Dim prevOwner As Person = _owner

  15:              _owner = Value

  16:   

  17:              If IsLoading Then Return 

  18:   

  19:              ' Remove an owner's reference to this building, if exists. 

  20:              If Not (prevOwner Is Nothing) AndAlso prevOwner.House Is Me Then 

  21:                  prevOwner.House = Nothing 

  22:              End If 

  23:   

  24:              ' Specify that the building is a new owner's house. 

  25:              If Not (_owner Is Nothing) Then 

  26:                  _owner.House = Me 

  27:              End If 

  28:   

  29:              OnChanged("Owner")

  30:   

  31:          End Set 

  32:      End Property 

  33:  End Class 

  34:   

XAF : Extend Built-in Property Editor's Functionality

This topic describes how to customize a built-in XAF Property Editor. The DatePropertyEditor will be customized to display date and time in the full format. The Property Editor control's dropdown will display the calendar and the clock in the Windows Vista style. The image below shows the resulting Property Editor:

Since the Property Editor inherits from the DatePropertyEditor class, which is the DXPropertyEditor class descendant, its settings can be accessed via the Repository Item. To apply the customization to the controls created both in the Detail View and List View, override the SetupRepositoryItem method. The PropertyEditor attribute is applied to the implemented Property Editor, to specify that it can be used for the String type properties:

   1:  Imports System

   2:   

   3:  Imports DevExpress.ExpressApp

   4:  Imports DevExpress.ExpressApp.Editors

   5:  Imports DevExpress.ExpressApp.Win.Editors

   6:  Imports DevExpress.ExpressApp.Model

   7:   

   8:  <PropertyEditor(GetType(DateTime), "CustomDateTimeEditor", False)> _

   9:  Public Class CustomDateTimeEditor

  10:      Inherits DatePropertyEditor

  11:      Public Sub New(ByVal objectType As Type, 
                            ByVal info As IModelMemberViewItem)

  12:          MyBase.New(objectType, info)

  13:      End Sub

  14:   

  15:      Protected Overrides Sub SetupRepositoryItem(ByVal item As 
            DevExpress.XtraEditors.Repository.RepositoryItem)

  16:          MyBase.SetupRepositoryItem(item)

  17:          DirectCast(item, RepositoryItemDateTimeEdit).VistaDisplayMode = _

  18:          DevExpress.Utils.DefaultBoolean.[True]

  19:          DirectCast(item, RepositoryItemDateTimeEdit).VistaEditTime = _

  20:          DevExpress.Utils.DefaultBoolean.[True]

  21:          DirectCast(item, RepositoryItemDateTimeEdit).Mask.EditMask = _

  22:          "MM.dd.yyyy hh:mm:ss"

  23:      End Sub

  24:  End Class

  25:   

XAF : Set Default Property For Object Attribute

Here we will set a default value for a property of a business class, In this example we will set the default 'Priority' property in DemoTask to 'Normal' state. To do this, first we want to build DemoTask Class with 'Priority' property:

   1:  Public Class DemoTask

   2:      Inherits Task

   3:      ' ...

   4:      Private fPriority As Priority

   5:      Public Property Priority() As Priority

   6:          Get

   7:              Return fPriority

   8:          End Get

   9:          Set(ByVal value As Priority)

  10:              SetPropertyValue("Priority", fPriority, value)

  11:          End Set

  12:      End Property

  13:      '...

  14:  End Class

• 'Priority' property added to DemoTask class

XAF : Implement One-to-Many Relationship

The following snippet of code present One-to-Many Relationship between Department and Contact business classes, in which Department object has many Contacts.
To implement the "One" part of the Department-Contacts relationship, decorate the Contact class Department property with the Association attribute.

   1:  <DefaultClassOptions()> _

   2:  Public Class Contact

   3:      Inherits Person

   4:      '...

   5:      Private fDepartment As Department

   6:      <Association("Department-Contacts", GetType(Department))> _

   7:      Public Property Department() As Department

   8:          Get

   9:              Return fDepartment

  10:          End Get

  11:          Set(ByVal value As Department)

  12:              SetPropertyValue("Department", fDepartment, value)

  13:          End Set

  14:      End Property

  15:      '...

  16:  End Class

  17:   

  18:   

XAF : Implement Many-to-Many Relationship

The following code snippet shows Many-to-Many Relationship between DemoTask and Contact business classes objects.

DemoTask Class:

   1:  Public Class DemoTask

   2:      Inherits Task

   3:      Public Sub New(ByVal session As Session)

   4:          MyBase.New(session)

   5:      End Sub

   6:      <Association("Contact-DemoTask", GetType(Contact))> _

   7:      Public ReadOnly Property Contacts() As XPCollection

   8:          Get

   9:              Return GetCollection("Contacts")

  10:          End Get

  11:      End Property

  12:  End Class

  13:   

  14:   

• The Association attribute is applied to the XPCollection type Contacts property, representing the collection of associated Contacts.
• The Association attribute is required when setting a relationship between objects
• The GetCollection method is used to return a collection in Contacts property getter implementation.

XAF : Building Domain Class

Business Class can be implemented in your application either from scratch by inherit your class from BaseObject or by using Business Class Library, which is contains the most common business classes such as Contact class which is include basic information about contact like FullName, SpouseName, FirstName and LastName. Note that only public members are mapped into database tables.


Create Business Class by inheriting from BaseObject:

   1:  Imports System

   2:  Imports System.ComponentModel

   3:   

   4:  Imports DevExpress.Xpo

   5:  Imports DevExpress.Data.Filtering

   6:   

   7:  Imports DevExpress.ExpressApp

   8:  Imports DevExpress.Persistent.Base

   9:  Imports DevExpress.Persistent.BaseImpl

  10:  Imports DevExpress.Persistent.Validation

  11:   

  12:   

  13:  <DefaultClassOptions()> _

  14:  Public Class Department

  15:      Inherits BaseObject

  16:      <Association("DepartmentContacts", GetType(Contact))> Public ReadOnly Property 
Contacts As XPCollection

  17:          Get

  18:              Return GetCollection("Contacts")

  19:          End Get

  20:      End Property

  21:      Private _departmentName As String

  22:      Public Property DepartmentName As String

  23:          Set(ByVal value As String)

  24:              SetPropertyValue("DepartmentName", Me._departmentName, value)

  25:          End Set

  26:          Get

  27:              Return Me._departmentName

  28:          End Get

  29:      End Property

  30:      Public Sub New(ByVal session As Session)

  31:          MyBase.New(session)

  32:          ' This constructor is used when an object is loaded from a persistent storage.

  33:          ' Do not place any code here or place it only when the IsLoading property is false:

  34:          ' if (!IsLoading){

  35:          '   It is now OK to place your initialization code here.

  36:          ' }

  37:          ' or as an alternative, move your initialization code into the AfterConstruction method.

  38:      End Sub

  39:      Public Overrides Sub AfterConstruction()

  40:          MyBase.AfterConstruction()

  41:          ' Place here your initialization code.

  42:      End Sub

  43:  End Class

XAF : Business Classes vs Database Tables

In an application where you have to deal with information, you most likely have database tables, database systems, SQL queries, records and columns. Using relational models is a traditional way to work with databases. Today, the most common approach to database access is probably ADO.NET technology. It has the DataSet type that grants a local copy of multiple interrelated database tables. Via the DataSet object, a user can locally execute various operations, with the content of a database being physically disconnected from the DBMS.

The eXpressApp Framework (XAF) concentrates its efforts on another flow of today's development: object-oriented data handling. The need to store object-oriented data appeared when object-oriented programming became pervasive. Currently, most modern, nontrivial applications use an object-oriented paradigm to model application domains. This means that you can abstract from any persistence details, and have a clean, simple, object-oriented API to perform data storage. You do not need to handle persistence details and internal data representation in data stores be they relational, object-based, or something else. Why should you deal with low-level constructs of the data-store model, such as rows and columns, and constantly translate them back and forth? Instead, concentrate on complex applications you are required to deliver.

The ability to use object-based data handling, instead of direct interaction with databases, leads to a layer that provides mapping of objects into database tables (Object-Relational Mapping tool). In the XAF, such a layer is provided by the eXpress Persistent Objects (XPO). The XPO provides reliability and flexibility in storing the information. Its simplicity comes from the fact that you do not need to learn the details of how the data is stored.