您的位置：首页 > 大数据 > 人工智能

自定义Domain Service时遇到实体不能更新的问题及其解决方案

2011-07-19 19:56 489 查看

这是在项目中的一个小问题。我们用到了自定义的Domain Service和自定义Entity，如果仅仅是读取数据，没有任何问题。但如果需要通过双向绑定，实现更新，则可能会遇到一个错误。类似下面这样

本文将重现这个问题，并分析原因和提供解决方案。

【备注】Domain Service看起来很不错，尤其是结合LINQ to Entity的话。但在使用自定义Domain Service时会遇到各种各样的问题，很多问题是让人莫名其妙的。我个人觉得这个设计模型还需要进一步完善的

1. 自定义业务实体

下面这个类型会被用到服务中返回文件类型映射的信息

using System.ComponentModel.DataAnnotations;

namespace SilverlightApplication3.Web
{
public class Employee
{
[Key]
public int ID { get; set; }
[Editable(true)]
public string FirstName { get; set; }
[Editable(true)]
public string LastName { get; set; }
}
}

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

2. 自定义Domain Service

namespace SilverlightApplication3.Web
{
using System.Linq;
using System.ServiceModel.DomainServices.Hosting;
using System.ServiceModel.DomainServices.Server;

// TODO: Create methods containing your application logic.
[EnableClientAccess()]
public class SampleDomainService : DomainService
{
public IQueryable<Employee> GetEmployees()
{
return new[]{
new Employee(){ID=1,FirstName="ares",LastName="chen"},
new Employee(){ID=2,FirstName="bill",LastName="gate"}}.AsQueryable();

}
}
}

3. 客户端的ViewModel

using System.Collections.ObjectModel;
using Microsoft.Practices.Prism.ViewModel;
using SilverlightApplication3.Web;
using System.ComponentModel;

namespace SilverlightApplication3.ViewModels
{
public class MainPageViewModel:NotificationObject
{

public MainPageViewModel()
{

if(DesignerProperties.IsInDesignTool) return;

var ctx = new SampleDomainContext();
ctx.Load<Employee>(ctx.GetEmployeesQuery(), (op) => {
Employees = new ObservableCollection<Employee>(op.Entities);
}, true);
}

private ObservableCollection<Employee> _Employees;
public ObservableCollection<Employee> Employees
{
get { return _Employees; }
set
{
if(_Employees != value)
{
_Employees = value;
RaisePropertyChanged("Employees");
}
}
}

}
}

4. 页面定义

<UserControl
xmlns:sdk="http://schemas.microsoft.com/winfx/2006/xaml/presentation/sdk"
x:Class="SilverlightApplication3.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"
d:DesignHeight="300"
d:DesignWidth="400"
xmlns:vm="clr-namespace:SilverlightApplication3.ViewModels">

<UserControl.DataContext>
<vm:MainPageViewModel></vm:MainPageViewModel>
</UserControl.DataContext>
<Grid
x:Name="LayoutRoot"
Background="White"
Margin="20">
<StackPanel>
<TextBlock
Text="Employee List"
FontSize="20"></TextBlock>
<sdk:DataGrid
Margin="10"
ItemsSource="{Binding Employees}"
AutoGenerateColumns="False">
<sdk:DataGrid.Columns>
<sdk:DataGridTextColumn
Binding="{Binding ID}"
Header="ID"></sdk:DataGridTextColumn>
<sdk:DataGridTextColumn
Binding="{Binding FirstName,Mode=TwoWay}"
Header="FirstName"></sdk:DataGridTextColumn>
<sdk:DataGridTextColumn
Binding="{Binding LastName,Mode=TwoWay}"
Header="LastName"></sdk:DataGridTextColumn>
</sdk:DataGrid.Columns>
</sdk:DataGrid>
</StackPanel>
</Grid>
</UserControl>

5. 测试运行

读取数据是没有问题的，但是如果我们去编辑FirstName或者LastName，就会发生如下的错误

这个错误确实让人看得云里雾里的。不是吗？你绝不会想到是要像下面这样解决

6. 添加一个Updatexxxx方法，使得Employee这个EntitySet可以被编辑

解决方案居然是要为Employee这个类型，添加一个特殊的方法，用Update做为前缀。看下面的例子

namespace SilverlightApplication3.Web
{
using System.Linq;
using System.ServiceModel.DomainServices.Hosting;
using System.ServiceModel.DomainServices.Server;

// TODO: Create methods containing your application logic.
[EnableClientAccess()]
public class SampleDomainService : DomainService
{
public IQueryable<Employee> GetEmployees()
{
return new[]{
new Employee(){ID=1,FirstName="ares",LastName="chen"},
new Employee(){ID=2,FirstName="bill",LastName="gate"}}.AsQueryable();

}

        /// <summary>
/// 这个方法用来更新员工
/// </summary>
/// <param name="e"></param>
public void UpdateEmployee(Employee e)
{
}

}
}

namespace SilverlightApplication3.Web
{
using System.Linq;
using System.ServiceModel.DomainServices.Hosting;
using System.ServiceModel.DomainServices.Server;

// TODO: Create methods containing your application logic.
[EnableClientAccess()]
public class SampleDomainService : DomainService
{
public IQueryable<Employee> GetEmployees()
{
return new[]{
new Employee(){ID=1,FirstName="ares",LastName="chen"},
new Employee(){ID=2,FirstName="bill",LastName="gate"}}.AsQueryable();

}

        /// <summary>
/// 这个方法用来更新员工
/// </summary>
/// <param name="e"></param>
[Update]
public void ModifyEmployee(Employee e)
{
}
}
}

7.再次运行测试（客户端代码无需任何修改）

请注意，第一行的FirstName已经被修改了（由ares改成了mike）

8. 分析问题的根源

那么，到底发生了什么呢？为什么添加了那个方法就又可以编辑了呢

我们可以打开客户端自动生成的那个文件来看一下，里面有一段代码很特殊

internal sealed class SampleDomainContextEntityContainer : EntityContainer
{

public SampleDomainContextEntityContainer()
{
this.CreateEntitySet<Employee>(EntitySetOperations.Edit);
}
}

#region Assembly System.ServiceModel.DomainServices.Client.dll, v2.0.50727
// C:\Program Files (x86)\Microsoft SDKs\RIA Services\v1.0\Libraries\Silverlight\System.ServiceModel.DomainServices.Client.dll
#endregion

using System;

namespace System.ServiceModel.DomainServices.Client
{
// Summary:
//     Enumeration of the types of operations permissable on an System.ServiceModel.DomainServices.Client.EntitySet.
[Flags]
public enum EntitySetOperations
{
// Summary:
//     Only read operations are permitted, no update operations are allowed.
None = 0,
//
// Summary:
//     New entities may be added
Add = 1,
//
// Summary:
//     Entities may be updated
Edit = 2,
//
// Summary:
//     Entities may be removed
Remove = 4,
//
// Summary:
//     Entities may be added, updated and removed
All = 7,
}
}

9.题外话：

我们在使用LINQ to Entity作为Domain Service的数据模型的时候，可能就意识不到这个问题，是因为我们可以在创建Domain Service的时候设置是否允许编辑

然后自动生成的Domain Service里面就自动具有了Update,Delete,Insert之类的方法，这样就允许这些业务实体支持更新了。

内容来自用户分享和网络整理，不保证内容的准确性，如有侵权内容，可联系管理员处理

标签：

相关文章推荐

新的分享

章节导航