How to: Initialize Business Objects with Default Property Values in Entity Framework 如何：在EF中用默认属性值初始化业务对象

When designing business classes, a common task is to ensure that a newly created business object is initialized with default property values. This topic explains how different types of properties can be initialized. As an example, a Contact business class will be implemented. After a Contact object is created, its properties will be initialized with default values.

设计业务类时，常见的任务是确保使用默认属性值初始化新创建的业务对象。本主题说明如何初始化不同类型的属性。例如，将实现联系人业务类。创建"联系人"对象后，其属性将用默认值初始化。

Tip 提示

A complete sample project is available in the DevExpress Code Examples database at http://www.devexpress.com/example=T209960

完整的示例项目可在 DevExpress 代码示例数据库中找到，http://www.devexpress.com/example=T209960

.

Tip 提示

A similar example for XPO is available in the How to: Initialize Business Objects with Default Property Values in XPO topic.

XPO 的类似示例在 XPO 主题中的"如何：使用默认属性值初始化业务对象"主题中提供。

Simple Property

简单属性

You can support an IXafEntityObject interface in your business classes. This interface declares the IXafEntityObject.OnCreated method intended for object initialization. The OnCreated method is called only once for an object - after the object is created. Whenever you need to initialize an object, place the initialization code into the OnCreated method body. The following code snippet demonstrates how simple value properties can be initialized.

您可以在业务类中支持 IXafEntityObject 接口。此接口声明用于对象初始化的 IXafEntityObject.OnCreated 方法。在创建对象后，仅对对象调用一次 OnCreated 方法。每当需要初始化对象时，将初始化代码放入 OnCreated 方法正文中。以下代码段演示如何初始化简单值属性。

public class Contact : Person, IXafEntityObject {
    //...
    void IXafEntityObject.OnCreated() {
        FirstName = "Sam";
        TitleOfCourtesy = TitleOfCourtesy.Mr;
    }
    void IXafEntityObject.OnLoaded() { }
    void IXafEntityObject.OnSaving() { }
}

To see another example of initializing a simple property, refer to the Initialize a Property After Creating an Object (EF) tutorial lesson.

要查看初始化简单属性的另一个示例，请参阅创建对象 （EF） 教程课后初始化属性。

Reference Property

引用属性

Initialization of reference properties differs from initialization of simple properties, primarily in that you may need to obtain a reference to an existing object. For this purpose, use the IObjectSpace.FindObject method of the object's Object Space. To access the Object Space from the business object code, you should support the IObjectSpaceLink interface. The following code snippet demonstrates how to initialize reference properties with new and existing objects.

引用属性的初始化不同于简单属性的初始化，主要是因为您可能需要获取对现有对象的引用。为此，请使用对象对象空间的 IObjectSpace.FindObject 方法。要从业务对象代码访问对象空间，应支持 IObjectSpaceLink 接口。以下代码段演示如何使用新对象和现有对象初始化引用属性。

public class Contact : Person, IXafEntityObject, IObjectSpaceLink {
    //...
    void IXafEntityObject.OnCreated() {
        // ...
        Address1 = objectSpace.CreateObject<Address>();
        Address1.Country = objectSpace.FindObject<Country>(CriteriaOperator.Parse("Name = 'USA'"));
        if (Address1.Country == null) {
            Address1.Country = objectSpace.CreateObject<Country>();
            Address1.Country.Name = "USA";
        }
        Manager = objectSpace.FindObject<Contact>(
            CriteriaOperator.Parse("FirstName = 'John' && LastName = 'Doe'"));
    }
    void IXafEntityObject.OnLoaded() { }
    void IXafEntityObject.OnSaving() { }
    private IObjectSpace objectSpace;
    IObjectSpace IObjectSpaceLink.ObjectSpace {
        get { return objectSpace; }
        set { objectSpace = value; }
    }
}

Collection Property

集合属性

The following code snippet demonstrates how to populate the Phones collection with predefined phone numbers.

以下代码段演示如何使用预定义的电话号码填充电话集合。

public class Contact : Person, IXafEntityObject, IObjectSpaceLink {
    //...
    void IXafEntityObject.OnCreated() {
        // ...
        PhoneNumber phone1 = objectSpace.FindObject<PhoneNumber>(
            CriteriaOperator.Parse("Number = '555-0101'"));
        PhoneNumber phone2 = objectSpace.FindObject<PhoneNumber>(
            CriteriaOperator.Parse("Number = '555-0102'"));
        PhoneNumbers.Add(phone1);
        PhoneNumbers.Add(phone2);
    }
    void IXafEntityObject.OnLoaded() { }
    void IXafEntityObject.OnSaving() { }
    private IObjectSpace objectSpace;
    IObjectSpace IObjectSpaceLink.ObjectSpace {
        get { return objectSpace; }
        set { objectSpace = value; }
    }
}

Calculated Property

计算属性

A calculated property value is automatically updated when the associated property values are changed. To learn how to implement a regular calculated property, refer to the Make a Property Calculable tutorial lesson. To learn how to implement a calculated property based on property values of the objects contained in a child object collection. Refer to the How to: Calculate a Property Value Based on Values from a Detail Collection help topic.

更改关联的属性值时，将自动更新计算的属性值。要了解如何实现常规计算属性，请参阅创建属性可计算教程课。了解如何实现基于子对象集合中包含的对象的属性值的计算属性。请参阅"如何：基于详细信息集合帮助中的值计算属性值"主题。

Initialize an Object Created via the New Action

初始化通过新操作创建的对象

In certain scenarios, you may need to initialize only objects created specifically via the New Action. To learn how to do this, refer to the How to: Initialize an Object Created Using the New Action help topic.

在某些情况下，您可能需要仅初始化通过"新建操作"专门创建的对象。要了解如何执行此操作，请参阅"如何：初始化使用"新建操作"帮助创建的对象主题。

Initialize a Property of a Child Object with a Value Taken from a Master Object

初始化子对象的属性，具有从主对象获取的值

You can set the default value for the child object's property within the setter of a property that refers to the master object.

您可以在引用主对象的属性的 setter 中设置子对象属性的默认值。

public class ChildObject {
    // ...
    public MasterObject MasterObject {
        get { return masterObject; }
        set {
            if (master == value) return;
            masterObject = value;
            if (value != null) {
                this.SomeProperty = value.DefaultForChildren;
            }
        }
    }
}

Since the reference property of a child object will not be initialized until committing changes, it is necessary to use a ViewController to initialize the child object depending on the master object (see How to: Initialize an Object Created Using the New Action).

由于子对象的引用属性在提交更改之前不会初始化，因此有必要使用 ViewController 根据主对象初始化子对象（请参阅：使用"新操作"创建的对象初始化）。