具有实体框架和更新记录的MVC存储库模式

Question

我试图在MVC应用程序中将存储库模式与EntityFramework一起使用来更新记录，但是db.SaveChanges（）方法没有保存到数据库中。 我没有遇到任何错误，可以逐步浏览代码，查看传递正确的变量以及记录变量的情况。

根据我一直在阅读的内容，我认为我的问题是我有两个数据库上下文实例（MyDBEntities）。 问题可能是将创建MyDBEntities实例的ReadRepository注入到WriteRepository中，WriteRepository也创建MyDBEntities实例。 我不太确定如何将实体注入到存储库中（假设这就是我需要做的）。

如果我尝试添加类似db.MyTable.Attach(record); 在db.SaveChanges()之前，我将在下面收到此错误，这使我认为我需要注入MyDBEntities() 。

An entity object cannot be referenced by multiple instances of IEntityChangeTracker.

控制器

public class MyController : Controller
{
    private IWriteRepository _writeRepository;

    public MyController(IWriteRepository writeRepository)
    {
        _writeRepository = writeRepository;
    }

    [HttpPost]
    public ActionResult MyPostMethod(MyViewModel model)
    {
        try
        {
            //Send to the repository to edit a record
            writeRepository.EditRecord(model);

            return new HttpStatusCodeResult(HttpStatusCode.OK);
        }
        catch
        {
            throw new HttpException(500, "Internal Server Error");
        }            
    }
}

写存储库

//The ReadRepository is injected into the WriteRepository to grab records from the database
public class WriteRepository : IWriteRepository
{
    private MyDBEntities db = new MyDBEntities();
    private IReadRepository _readRepository;

    public WriteRepository(IReadRepository readeadRepository)
    {
        _readRepository = readRepository;
    }        

    public void EditRecord(MyViewModel model)
    {
        //Get the specific record to be updated
        var record = readRepository.GetRecord(model.ID);

        //Update the data
        record.FirstName = model.Name;

        //This isn't saving
        db.SaveChanges();
    }
}

阅读存储库

public class ReadRepository : IReadRepository
{
    private MyDBEntities db = new MyDBEntities();

    //Provides the record to the write repository to edit
    public MyTable GetRecord(int ID)
    {
        var record = (from t in db.MyTable
                      where t.ID == ID
                      select t).SingleOrDefault();

        return record;
    }
}

Answer 1

从MyController代码中，您好像已经在使用Inversion of Control框架，因此，请按以下方式更新ReadRepository和WriteRepository类：

读存储库

public class ReadRepository : IReadRepository
{
    private MyDBEntities db;

    public ReadRepository(MyDBEntities myDbEntities) 
    {
        db = myDbEntities;
    }

    //Provides the record to the write repository to edit
    public MyTable GetRecord(int ID)
    {
        var record = (from t in db.MyTable
                      where t.ID == ID
                      select t).SingleOrDefault();

        return record;
    }
}

WriteRepository

public class WriteRepository : IWriteRepository
{
    private MyDBEntities db;
    private IReadRepository _readRepository;

    public WriteRepository(MyDBEntities myDbEntities, IReadRepository readeadRepository)
    {
        db = myDbEntities;
        _readRepository = readRepository;
    }        

    public void EditRecord(MyViewModel model)
    {
        //Get the specific record to be updated
        var record = readRepository.GetRecord(model.ID);

        //Update the data
        record.FirstName = model.Name;

        //This isn't saving
        db.SaveChanges();
    }
}

无论您ReadRepository和WriteRepository取决于MyDBEntities做工作的一个实例，因此就应该在这些类的构造函数依赖，并让你控制框架手柄的反转创造它，而不是创造MyDBEntities自己的新实例。

确保在Inversion of Control框架的注册中，您将MyDBEntities实例注册为作用域或每个请求，而不是临时的。 您想确保在每个请求上，您的ReadRepository和WriteRepository都注入了MyDBEntities类的相同实例，而不是现在的两个单独实例。

如下更新您的Unity配置：

UnityConfig.cs

在每个请求范围内向 Unity注册您的MyDBEntities类。

public class UnityConfig
{
    // ... other methods ...

    public static void RegisterTypes(IUnityContainer container)
    {
        // ... other registrations ...
        container.RegisterType<IReadRepository, ReadRepository>();
        container.RegisterType<IWriteRepository, WriteRepository>();
        container.RegisterType<MyDBEntities>(new PerRequestLifetimeManager());
        // ... other registrations ...
    }
}

UnityMvcActivator.cs

通过取消注释TODO下的行，在Unity中启用每个请求范围。

public static class UnityWebActivator
{
    public static void Start()
    {
        // ... start code ...
        // TODO: Uncomment if you want to use PerRequestLifetimeManager
        Microsoft.Web.Infrastructure.DynamicModuleHelper.DynamicModuleUtility.RegisterModule(typeof(UnityPerRequestHttpModule));
    }

    // ... other methods ...
}