Supply Initial Data提供初始数据 （EF）

Posted 2021-03-23 foreachlife

Note

Before proceeding, take a moment to review the Inherit from the Business Class Library Class (EF) lesson.

注意
在继续之前，请花点时间复习从商务舱库类 （EF） 课程继承。

 

• Open the Updater.cs (Updater.vb) file, located in the MySolution.Module project‘s Database Update folder. Add the following code to the ModuleUpdater.UpdateDatabaseAfterUpdateSchema method.

• 打开位于 MySolution.模块项目的数据库更新文件夹中的Updater.cs（Updater.vb）文件。将以下代码添加到模块更新器.更新数据库后更新架构方法。

  using MySolution.Module.BusinessObjects;
  //...
  
  public class Updater : DevExpress.ExpressApp.Updating.ModuleUpdater {
      //...
          public override void UpdateDatabaseAfterUpdateSchema() {
          base.UpdateDatabaseAfterUpdateSchema();
  
          Contact contactMary = ObjectSpace.FindObject<Contact>(
              CriteriaOperator.Parse("FirstName == ‘Mary‘ && LastName == ‘Tellitson‘"));
          if (contactMary == null) {
              contactMary = ObjectSpace.CreateObject<Contact>();
              contactMary.FirstName = "Mary";
              contactMary.LastName = "Tellitson";
              contactMary.Email = "[e-mail]";
              contactMary.Birthday = new DateTime(1980, 11, 27);
          }
          //...
          ObjectSpace.CommitChanges();
      }
  }

   

  After adding the code above, the Contact object will be created in the application database, if it does not already exist.

• 添加上述代码后，如果联系人对象不存在，将在应用程序数据库中创建该对象。

 

• Each time you run the application, it compares the application version with the database version and finds changes in the application or database. If the database version is lower than the application version, the application raises the XafApplication.DatabaseVersionMismatch event. This event is handled by the WinForms and ASP.NET applications in a solution template. When the application runs in debug mode, this event handler uses the built-in Database Updater to update the application‘s database. After the database schema is updated, the ModuleUpdater.UpdateDatabaseAfterUpdateSchema method is called. In this method, you can save the required business objects to the database.

• 每次运行应用程序时，它都会将应用程序版本与数据库版本进行比较，并在应用程序或数据库中查找更改。如果数据库版本低于应用程序版本，则应用程序将引发 XafApplication.DatabaseVersion 不匹配事件。此事件由 WinForms 处理，并在解决方案模板中ASP.NET应用程序。当应用程序在调试模式下运行时，此事件处理程序使用内置的数据库更新程序来更新应用程序的数据库。更新数据库架构后，将调用模块更新器.Updatedatabase 后更新架构方法。在此方法中，可以将所需的业务对象保存到数据库中。

 

• As you can see in the code above, eXpressApp Framework (XAF) uses an Object Space object to manipulate persistent objects (see Create, Read, Update and Delete Data)

• .如上述代码所示，eXpressApp 框架 （XAF） 使用对象空间对象操作持久对象（请参阅创建、读取、更新和删除数据）。

 

• To specify the criteria passed as a parameter in the BaseObjectSpace.FindObject method call, the CriteriaOperator is used. Its CriteriaOperator.Parse method converts a string, specifying a criteria expression to its CriteriaOperator equivalent. To learn more on how to specify criteria, refer to the Ways to Build Criteria topic.

• 要指定在 BaseObjectSpace.FindObject 方法调用中作为参数传递的条件，将使用条件运算符。其 CriteriaOperator.Parse 方法转换字符串，将条件表达式指定为其条件运算符等效项。要了解有关如何指定条件的详细信息，请参阅生成条件的方法主题。

 

• Run the WinForms or ASP.NET application. Select the Contact item in the navigation control. Notice that the new contact, "Mary Tellitson", appears in the list to the right.

• 运行 WinForms 或ASP.NET应用程序。选择导航控件中的"联系人"项。请注意，新的联系人"玛丽·特利森"出现在右侧的列表中。

  

Note

Note that in the Inherit from the Business Class Library Class (EF) lesson, the database initializer was set to clear the database in case the business model changes. This means that all objects created at runtime will be deleted after the next change in the business model. It is recommended that you use the approach described in this lesson to create all objects required for testing purposes. They will persist in your application regardless of the database.

注意

请注意，在从 Business 类库类 （EF） 继承一课中，数据库初始化程序已设置为清除数据库，以防业务模型发生更改。这意味着在运行时创建的所有对象都将在业务模型中的下一次更改后删除。建议您使用本课中描述的方法创建测试所需的所有对象。无论数据库如何，它们都将保留在应用程序中。

 

You can see the code for this tutorial in the EFDemo.Module | Database Update | Updater.cs (Updater.vb) file of the EF Demo (Code First) demo installed with XAF. By default, the EF Demo (Code First) application is installed in %PUBLIC%DocumentsDevExpress Demos 19.2ComponentseXpressApp FrameworkEFDemoCodeFirst.

您可以在 EFDemo.模块中查看本教程的代码。数据库更新 |Updater.cs （Updater.vb） 文件 EF 演示（代码优先）演示安装与 XAF。默认情况下，EF 演示（代码优先）应用程序安装在 %PUBLIC%_文档_DevExpress 演示 19.2_组件_eXpressApp 框架_EFDemoCodeFirst 中。