How to: Generate Persistent Objects for Existing Data Tables

• Oct 29, 2020
• 5 minutes to read

The eXpress Persistent Objects library provides a design-time wizard that allows you to generate persistent objects for one or more data tables in your database. Only specify connection settings to the database, and select target tables and columns. The wizard will automatically generate persistent objects for the selected tables.

Note

Data tables whose primary keys are composed of several columns are not supported by XPO. The wizard will not process these tables.

Generating Persistent Objects

1. In the Solution Explorer, add a new project to the solution.

   

   Name is ‘BusinessObjects’.

   

2. Select the Add->New Item… context menu option.

   

3. Select the Persistent Classes item in the dialog window and click Add.

   

4. The wizard will open and ask you to specify connection settings to the database containing the target data table(s).

   

   The wizard displays all database engines supported by XPO. Use the Provider combo box to select the required database type. Note that the corresponding database provider assembly must be registered in the Global Assembly Cache (GAC) on your machine or the wizard will fail.

   Click Next after connection settings have been specified.

5. In the next step, the wizard displays a list of tables that can be mapped to persistent objects. A table whose primary key is composed of several columns will be unavailable for selection.

   

   Select a table(s) to be mapped to a persistent object(s), and for each table select columns that will be mapped to the persistent object’s properties. For unchecked columns, persistent properties will not be generated.

   The names of persistent classes and their properties will match the names of selected tables and their columns. To rename the classes and properties, use the Rename buttons in the Tables and Columns panes. The classes and properties with modified names will still be mapped to corresponding tables and columns using the PersistentAttribute attribute.

   Click Finish to close the wizard and generate the persistent classes. Below is a code snippet of such a class.

   C#

   using System;
   using DevExpress.Xpo;
   namespace Northwind {
   
       public class Customers : XPLiteObject {
           string fCustomerID;
           [Key]
           [Size(5)]
           public string CustomerID {
               get { return fCustomerID; }
               set { SetPropertyValue<string>("CustomerID", ref fCustomerID, value); }
           }
           string fCompanyName;
           [Size(40)]
           public string CompanyName {
               get { return fCompanyName; }
               set { SetPropertyValue<string>("CompanyName", ref fCompanyName, value); }
           }
           string fContactName;
           [Size(30)]
           public string ContactName {
               get { return fContactName; }
               set { SetPropertyValue<string>("ContactName", ref fContactName, value); }
           }
           string fContactTitle;
           [Size(30)]
           public string ContactTitle {
               get { return fContactTitle; }
               set { SetPropertyValue<string>("ContactTitle", ref fContactTitle, value); }
           }
           // ...
       }
   }
   

   VB.NET

   Namespace Northwind
       Public Class Customers
           Inherits XPLiteObject
   
           Private fCustomerID As String
   
           <Key>
           <Size(5)>
           Public Property CustomerID As String
               Get
                   Return fCustomerID
               End Get
               Set(ByVal value As String)
                   SetPropertyValue(Of String)("CustomerID", fCustomerID, value)
               End Set
           End Property
   
           Private fCompanyName As String
   
           <Size(40)>
           Public Property CompanyName As String
               Get
                   Return fCompanyName
               End Get
               Set(ByVal value As String)
                   SetPropertyValue(Of String)("CompanyName", fCompanyName, value)
               End Set
           End Property
   
           Private fContactName As String
   
           <Size(30)>
           Public Property ContactName As String
               Get
                   Return fContactName
               End Get
               Set(ByVal value As String)
                   SetPropertyValue(Of String)("ContactName", fContactName, value)
               End Set
           End Property
   
           Private fContactTitle As String
   
           <Size(30)>
           Public Property ContactTitle As String
               Get
                   Return fContactTitle
               End Get
               Set(ByVal value As String)
                   SetPropertyValue(Of String)("ContactTitle", fContactTitle, value)
               End Set
           End Property
       End Class
   End Namespace
   

6. Add a reference to the BusinessObjects project and rebuild the solution.

   

   

Binding ASPxGridView

• Drop the XpoDataSource component on the Page and specify its TypeName property.

  

• Connect XPO to your database server. To do this, handle the Application_Start event in the Global.asax module of your website to create an IDataLayer object. We suggest that you use the ThreadSafeDataLayer in ASP.NET applications.

  C#

  void Application_Start(object sender, EventArgs e) {
      // It's supposed that you've already created the NWind database within the App_Data folder.
      string conn = DevExpress.Xpo.DB.AccessConnectionProvider.GetConnectionString(
        Server.MapPath("~\\App_Data\\nwind.mdb"));
      DevExpress.Xpo.Metadata.XPDictionary dict = new DevExpress.Xpo.Metadata.ReflectionDictionary();
      // Initialize the XPO dictionary.
      dict.GetDataStoreSchema(typeof(Northwind.Customers).Assembly);
      DevExpress.Xpo.DB.IDataStore store = DevExpress.Xpo.XpoDefault.GetConnectionProvider(conn,
                             DevExpress.Xpo.DB.AutoCreateOption.SchemaAlreadyExists);
      DevExpress.Xpo.XpoDefault.DataLayer = new DevExpress.Xpo.ThreadSafeDataLayer(dict, store);
      DevExpress.Xpo.XpoDefault.Session = null;
  }
  

  VB.NET

  Private Sub Application_Start(ByVal sender As Object, ByVal e As EventArgs)
      Dim conn As String = DevExpress.Xpo.DB.AccessConnectionProvider.GetConnectionString(Server.MapPath("~\App_Data\nwind.mdb"))
      Dim dict As DevExpress.Xpo.Metadata.XPDictionary = New DevExpress.Xpo.Metadata.ReflectionDictionary()
      dict.GetDataStoreSchema(GetType(Northwind.Customers).Assembly)
      Dim store As DevExpress.Xpo.DB.IDataStore = DevExpress.Xpo.XpoDefault.GetConnectionProvider(conn, DevExpress.Xpo.DB.AutoCreateOption.SchemaAlreadyExists)
      DevExpress.Xpo.XpoDefault.DataLayer = New DevExpress.Xpo.ThreadSafeDataLayer(dict, store)
      DevExpress.Xpo.XpoDefault.Session = Nothing
  End Sub
  

• Handle the Web form’s Init event to create a Session for the XpoDataSource component. The session must be linked to your DataLayer.

  C#

  using DevExpress.Xpo;
  
  Session session1;
  protected void Page_Init(object sender, EventArgs e) {
      session1 = new Session();
      XpoDataSource1.Session = session1;
  }
  

  VB.NET

  Private session1 As Session
  
      Protected Sub Page_Init(ByVal sender As Object, ByVal e As EventArgs)
          session1 = New Session()
          XpoDataSource1.Session = session1
      End Sub
  

• We recommend that you create an XPO Session for each request. To do this, create a new session for each page and dispose of it by overriding the Page.Render method.

  C#

  protected override void Render(HtmlTextWriter writer) {
      base.Render(writer);
      session1.Dispose();
  }
  

  VB.NET

  Protected Overrides Sub Render(ByVal writer As HtmlTextWriter)
      MyBase.Render(writer)
      session1.Dispose()
  End Sub
  

• Drop the ASPxGridView control on the Page and bind it to XpoDataSource.

Results

Run the application. The image below shows the result.