Implement Dependent Reference Properties实现依赖引用属性（EF）

In this lesson, you will learn how to implement properties whose values can depend on other properties. The Manager property will be added to the Contact class. By default, it will be represented by a lookup editor containing all Contacts that exist in the database. However, you may need this editor to contain Contacts from the same Department. In addition, you may need the Position of these Contacts to be "Manager". To do this, use the DataSourcePropertyAttribute and DataSourceCriteriaAttribute attributes for the Manager property.

在本课中，您将学习如何实现其值可以依赖于其他属性的属性。"管理器"属性将添加到"联系人"类中。默认情况下，它将由包含数据库中存在的所有联系人的查找编辑器表示。但是，您可能需要此编辑器包含来自同一部门的联系人。此外，您可能需要这些联系人的位置是"经理"。为此，请使用 Manager 属性的 DataSourceProperty 属性和数据源标准属性属性。

Note

Before proceeding, take a moment to review the following lessons.

Inherit from the Business Class Library Class (EF)
Implement Custom Business Classes and Reference Properties (EF)
Set a One-to-Many Relationship (EF)

Add a new Manager property of the Contact type to the Contact class. Apply the DataSourceProperty attribute to this property, as shown below.
注意
在继续之前，请花点时间复习以下课程。
从业务类库类（EF）继承
实现自定义业务类和参考属性（EF）
设置一对多关系（EF）
将"联系人"类型的新的"管理器"属性添加到"联系人"类。将 DataSourceProperty 属性应用于此属性，如下所示。
```
using DevExpress.Persistent.Base;

//...

public class Contact : Person {

    public Contact() {

        //...

        Subordinates = new List<Contact>();

    }

    //...

    [DataSourceProperty("Department.Contacts")]

    public virtual Contact Manager { get; set; }

    public virtual IList<Contact> Subordinates { get; set; }

}
```
Note

In EF, you always need to implement both "sides" of the relation. This means that each Contact must have a Manager and a list of Subordinates.

With the DataSourceProperty attribute applied, the Manager lookup editor will contain Contact objects that are specified by the Department object's Contacts property.
注意
在 EF 中，始终需要实现关系的两个"边"。这意味着每个联系人都必须有一个经理和一个下属列表。
应用 DataSourceProperty 属性后，Manager 查找编辑器将包含由"部门"对象的"联系人"属性指定的联系人对象。
Run the application and select Contact in the drop-down list of the New combo box. The Contact Detail View will be invoked. Specify the Department property and expand the Manager lookup editor. Make sure that the Department property of the listed objects is the same as those you specified above.
运行该应用程序，并在"新建组合"框的下拉列表中选择"联系人"。将调用"联系人详细信息"视图。指定"部门"属性并展开"管理器查找"编辑器。确保列出的对象的"部门"属性与您上面指定的对象相同。
Apply the DataSourceCriteria attribute to the Contact class' Manager property as shown below.
将"数据源标准"属性应用于联系人类的管理器属性，如下所示。
```
public class Contact : Person {

    //...

    [DataSourceProperty("Department.Contacts")]

    [DataSourceCriteria("Position.Title = 'Manager'")]

    public virtual Contact Manager { get; set; }

}
```
With the DataSourceCriteria attribute applied, the Manager lookup editor will contain Contact objects that satisfy the criteria specified in the attribute parameter.
Run the application. Set the Position property to "Manager" for several Contact objects.
应用 DataSourceCriteria 属性后，Manager 查找编辑器将包含满足属性参数中指定的条件的"联系人"对象。
运行应用程序。将"位置"属性设置为多个"联系人"对象的"管理器"。
Select Contact in the New () button's drop-down list. The Contact Detail View will be invoked. Specify the Department property and expand the Manager lookup editor. Check to make sure that the Position property is set to "Manager" for each of the listed objects.
在"新建（new_dropdown_btn）"按钮的下拉列表中选择"联系人"。将调用"联系人详细信息"视图。指定"部门"属性并展开"管理器查找"编辑器。检查以确保每个列出的对象的"位置"属性设置为"管理器"。
If the Department property is not specified for a Contact, you can provide another data source for the Manager lookup editor. To do this, specify the second parameter for the DataSourceProperty attribute. In the code below, this parameter is set to the DataSourcePropertyIsNullMode.SelectAll value. You can also set the DataSourcePropertyIsNullMode.SelectNothing or DataSourcePropertyIsNullMode.CustomCriteria values. In the latter case, a third parameter is required to specify a criterion.
如果未为联系人指定"部门"属性，则可以为 Manager 查找编辑器提供其他数据源。为此，请为 DataSourceProperty 属性指定第二个参数。在下面的代码中，此参数设置为 DataSourcePropertyIsNullMode。您还可以设置"数据源属性"NullMode。在后一种情况下，需要第三个参数来指定条件。
```
public class Contact : Person {

    //...

    [DataSourceProperty("Department.Contacts", DataSourcePropertyIsNullMode.SelectAll)]

    [DataSourceCriteria("Position.Title = 'Manager'")]

    public virtual Contact Manager { get; set; }

}
```
The code above will show all contacts in the Manager lookup editor if the Department property is not specified.
Run the application and check the results.
如果未指定"部门"属性，则上述代码将显示"管理器查找"编辑器中的所有联系人。
运行应用程序并检查结果。

You can see the code demonstrated in this lesson in the MySolution.Module | Data | Contact.cs (Contact.vb) file of the EF Demo (Code First) installed with XAF. By default, the EF Demo (Code First) application is installed in %PUBLIC%\Documents\DevExpress Demos 19.2\Components\eXpressApp Framework\EFDemoCodeFirst.

您可以在 MySolution.模块中看到本课中演示的代码。数据 |Contact.cs（Contact.vb）文件与XAF一起安装的EF演示（代码优先）文件。默认情况下，EF 演示（代码优先）应用程序安装在 %PUBLIC%\Documents\DevExpress Demos 19.2\Components\eXpressApp Framework\EFDemoCodeFirst中。