【发布时间】：2011-12-10 00:33:26
【问题描述】：
考虑这个简单的模型和视图模型场景：
public class SomeModel
{
public virtual Company company {get; set;}
public string name {get; set;}
public string address {get; set;}
//some other few tens of properties
}
public class SomeViewModel
{
public Company company {get; set;}
public string name {get; set;}
public string address {get; set;}
//some other few tens of properties
}
出现的问题是：
我有一个不需要公司的编辑页面，所以我不从数据库中获取它。现在，当提交表单时，我会这样做：
SomeModel destinationModel = someContext.SomeModel.Include("Company").Where( i => i.Id == id) // assume id is available from somewhere.
然后我做一个
Company oldCompany = destinationModel.company; // save it before mapper assigns it null
Mapper.Map(sourceViewModel,destinationModel);
//After this piece of line my company in destinationModel will be null because sourceViewModel's company is null. Great!!
//so I assign old company to it
destinationModel.company = oldCompany;
context.Entry(destinationModel).State = EntityState.Modified;
context.SaveChanges();
问题是即使我将 oldCompany 分配给我的公司，在 savechanges 之后它在数据库中仍然为空。
注意：
如果我更改这些行：
destinationModel.company = oldCompany;
context.Entry(destinationModel).State = EntityState.Modified;
context.SaveChanges();
对这些：
context.Entry(destinationModel).State = EntityState.Modified;
destinationModel.company = oldCompany;
context.Entry(destinationModel).State = EntityState.Modified;
context.SaveChanges();
请注意，我更改了 2 次状态，它工作正常。可能是什么问题？这是 ef 4.1 的错误吗？
这是解决该问题的示例控制台应用程序：
using System;
using System.Linq;
using System.Data.Entity;
using System.ComponentModel.DataAnnotations;
using AutoMapper;
namespace Slauma
{
public class SlaumaContext : DbContext
{
public DbSet<Company> Companies { get; set; }
public DbSet<MyModel> MyModels { get; set; }
public SlaumaContext()
{
this.Configuration.AutoDetectChangesEnabled = true;
this.Configuration.LazyLoadingEnabled = true;
}
}
public class MyModel
{
public int Id { get; set; }
public string Foo { get; set; }
[ForeignKey("CompanyId")]
public virtual Company Company { get; set; }
public int? CompanyId { get; set; }
}
public class Company
{
public int Id { get; set; }
public string Name { get; set; }
}
public class MyViewModel
{
public string Foo { get; set; }
public Company Company { get; set; }
public int? CompanyId { get; set; }
}
class Program
{
static void Main(string[] args)
{
Database.SetInitializer<SlaumaContext>(new DropCreateDatabaseIfModelChanges<SlaumaContext>());
SlaumaContext slaumaContext = new SlaumaContext();
Company company = new Company { Name = "Microsoft" };
MyModel myModel = new MyModel { Company = company, Foo = "Foo"};
slaumaContext.Companies.Add(company);
slaumaContext.MyModels.Add(myModel);
slaumaContext.SaveChanges();
Mapper.CreateMap<MyModel, MyViewModel>();
Mapper.CreateMap<MyViewModel, MyModel>();
//fetch the company
MyModel dest = slaumaContext.MyModels.Include("Company").Where( c => c.Id == 1).First(); //hardcoded for demo
Company oldCompany = dest.Company;
//creating a viewmodel
MyViewModel source = new MyViewModel();
source.Company = null;
source.CompanyId = null;
source.Foo = "foo hoo";
Mapper.Map(source, dest); // company null in dest
//uncomment this line then only it will work else it won't is this bug?
//slaumaContext.Entry(dest).State = System.Data.EntityState.Modified;
dest.Company = oldCompany;
slaumaContext.Entry(dest).State = System.Data.EntityState.Modified;
slaumaContext.SaveChanges();
Console.ReadKey();
}
}
}
【问题讨论】：
-
SomeModel和/或SomeViewModel中的Company是否有外键属性，例如CompanyId？当您知道 ViewModel 中的null是null时，为什么还要使用Include加载Company？在我看来，您可以删除Include。 -
外键属性是否可以为空并且也在
SomeViewModel中？在Mapper.Map之后会发生什么，它会覆盖destinationModel中的FK 值吗？ -
@Slauma：是的，你说得非常正确。外键可以为空。是的，在 Mapper.Map 之后 fk 值为空，但我明确地为其分配了一个值，但它没有效果。它只“喜欢”null。
-
您能在上面的代码中展示您对 FK 属性所做的确切操作吗？不知怎的，我觉得有问题。
-
@Slauma：我创建了一个简单的演示应用程序。请阅读我编辑的问题。您可以将源代码粘贴到控制台应用程序中并告诉我为什么会这样！
标签： c# entity-framework ef-code-first automapper ef4-code-only