Entity Framework 6 - Unity 的依赖注入 - 存储库模式 - 添加或更新多对多关系的异常

Question

在 Entity Framework 中添加具有多对多映射的新值时遇到问题。我知道 unit of work pattern，但在我们的解决方案中，我们希望保留一个简单的存储库模式，而不是包含所有内容的工作单元 class。这是可能的还是我应该立即实施 Unit of Work ？

如果我不使用下面的 iSupplierRepository，将添加一个供应商，但它总是会添加一个 new，即使已经存在一个具有该名称的供应商。

错误：

The relationship between the two objects cannot be defined because they are attached to different ObjectContext objects.

存储库示例：

public class SupplierRepository : IntEntityRepository<Supplier, DbContext>, ISupplierRepository
{
    public SupplierRepository(DbContext context) : base(context, context.Suppliers)
    {
    }
}

继承的存储库：

public class IntEntityRepository<TEntity, TContext> : EntityRepository<TEntity, TContext, int>
    where TEntity : class, IEntity<int>
    where TContext : BaseIdentityDbContext
{
    public IntEntityRepository(TContext context, IDbSet<TEntity> set) : base(context, set)
    {
    }

    public override async Task<TEntity> GetAsync(int id)
    {
        return (await GetAsync(entity => entity.Id == id)).SingleOrDefault();
    }
...

 public abstract class EntityRepository<TEntity, TContext, TId> : IEntityRepository<TEntity, TId>
    where TEntity : class, IEntity<TId>
    where TContext : BaseIdentityDbContext
{
    protected TContext Context { get; }
    protected IDbSet<TEntity> Set { get; }

     protected EntityRepository(TContext context, IDbSet<TEntity> set)
     {
         Context = context;
         Set = set;
     }

     public abstract Task<TEntity> GetAsync(TId id);
...

统一：

container.RegisterType<ISupplierRepository, SupplierRepository>();
container.RegisterType<IContactRepository, ContactRepository>();

控制器：

private readonly IContactRepository iContactRepository;
private readonly ISupplierRepository iSupplierRepository;

public ContactsController(IContactRepository iContactRepository, ISupplierRepository iSupplierRepository)
{
    this.iContactRepository = iContactRepository;
    this.iSupplierRepository = iSupplierRepository;
}

[HttpPut]
[Route("UpdateContact/{id}")]
public async Task<IHttpActionResult> UpdateContact(ContactViewModel contactVm, int id)
{
    try
    {
        var supplierList = new List<Supplier>();
        foreach (var contactVmSupplier in contactVm.Suppliers)
        {
            var supplier = await iSupplierRepository.GetAsync(contactVmSupplier.Id);
            supplierList.Add(supplier);
        }

        var contactOriginal = await iContactRepository.GetAsync(id);
        var updatedContact = Mapper.Map<ContactViewModel, Contact>(contactVm, contactOriginal);
        updatedContact.Suppliers = supplierList;

        await iContactRepository.UpdateAsync(updatedContact);
        return Ok();
    }
    catch (Exception e)
    {
        throw new Exception("Could not update a contact", e);
    }

}

视图模型：

public class ContactViewModel
{
    public int Id { get; set; }

    public string Name { get; set; }

    public ICollection<SupplierViewModel> Suppliers { get; set; }
}

public class SupplierViewModel
{
    public int Id { get; set; }

    public string Name { get; set; }
}

型号：

public class Contact : IEntity<int>
{
    public Contact()
    {
        Suppliers = new List<Supplier>();
    }

    [Key]
    public int Id { get; set; }

    public DateTime Created { get; set; }

    public DateTime Updated { get; set; }

    public string Name { get; set; }

    public ICollection<Supplier> Suppliers { get; set; }

}

public class Supplier: IEntity<int>
{
    public Supplier()
    {
        Contacts = new List<Contact>();
    }
    [Key]
    public int Id { get; set; }

    public DateTime Created { get; set; }

    public DateTime Updated { get; set; }

    public string Name { get; set; }

    public virtual ICollection<Contact> Contacts { get; set; }
}

Answer 1

更新：改用 Randy Levy 的回答。

我在这里的建议是根本不要使用 Repository 或 UoW。 EF 已经实施了它们。尝试重新实现它们时会遇到很多问题。

至于您遇到异常的具体问题：您必须为您的实体使用相同的 DbContext。同时，您不希望将 DbContext 用作 Singleton，而是按请求使用它。可能会找到一个可能的解决方案 here.

Application_BeginRequest(...)
{
  var childContainer = _container.CreateChildContainer();
  HttpContext.Items["container"] = childContainer;
  childContainer.RegisterType<ObjectContext, MyContext>
     (new ContainerControlledLifetimeManager());
}

Application_EndRequest(...)
{
  var container = HttpContext.Items["container"] as IUnityContainer
  if(container != null)
    container.Dispose();
}

Answer 2

这样解决了，依赖注入来自教程Dependency Injection in ASP.NET Web API 2。

https://docs.microsoft.com/en-us/aspnet/web-api/overview/advanced/dependency-injection

App_Start -> WebApiConfig

public static void Register(HttpConfiguration config)
{
    UnityConfig.ConfigureUnity(config);
...

统一配置：

public static void ConfigureUnity(HttpConfiguration config)
{
    var context = new DbContext();
    var container = new UnityContainer();
    container.RegisterType<ISupplierRepository, SupplierRepository>(new InjectionConstructor(context));
    container.RegisterType<IContactRepository, ContactRepository>(new InjectionConstructor(context));
    config.DependencyResolver = new UnityResolver(container);
}

Answer 3

如果安装 Unity bootstrapper for ASP.NET Web API package, a UnityHierarchicalDependencyResolver 可用，它将为每个 IHttpController 分辨率使用一个新的子容器，有效地使所有注册每个请求解析 HierarchicalLifetimeManager 以便所有存储库实例在控制器中将使用相同的 DbContext.

NuGet 包还将在 App_Start 中安装一些使用 WebActivatorEx 的引导代码。您可以使用此方法或更改以与您现在使用的内容保持一致。根据您发布的代码，它看起来像：

public static void ConfigureUnity(HttpConfiguration config)
{
    var container = new UnityContainer();
    container.RegisterType<DbContext>(new HierarchicalLifetimeManager());
    container.RegisterType<ISupplierRepository, SupplierRepository>();
    container.RegisterType<IContactRepository, ContactRepository>();
    config.DependencyResolver = new UnityHierarchicalDependencyResolver(container);
}

Entity Framework 6 - Unity 的依赖注入 - 存储库模式 - 添加或更新多对多关系的异常

Entity Framework 6 - Dependency Injection with Unity - Repository pattern - Add or Update exception for many to many relationship

c#

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entity-framework-6