我使用EF 4.1 with Repository和DbContext .. POCO with T4 template。 对于每个存储库，我使用单独的DbContext。
我需要更新具有相关属性的对象，此时我收到此错误
An entity object cannot be referenced by multiple instances of IEntityChangeTracker.
我认为我的问题是beacuse eventObj，而candidate是从不同的存储库创建的。
所以我试图用这段代码解决问题，但没有成功。
我的问题？
是否可以从其上下文中删除候选人？
public void UpdateAddingCandidate(Event eventObj, Candidate candidate){
Event updatedEvent = new Event();
Candidate updatedCandidate = new Candidate();
updatedEvent = eventObj;
updatedCandidate = candidate;
updatedEvent.Candidate = updatedCandidate;
db.Entry(updatedEvent).State = EntityState.Modified;
}
修改
public void UpdateAddingCandidate(Event eventObj, Candidate candidate)
{
/*
db.Events.AsNoTracking();
db.Candidates.AsNoTracking();
*/
db.Entry(eventObj).State = EntityState.Detached;
db.Entry(candidate).State = EntityState.Detached;
Event updatedEvent = new Event();
Candidate updatedCandidate = new Candidate();
updatedEvent = eventObj;
updatedCandidate = candidate;
updatedEvent.Candidate = updatedCandidate;
db.Entry(updatedEvent).State = EntityState.Detached;
db.Entry(updatedEvent).State = EntityState.Modified;
}
答案 0 :(得分：14)
不仅仅使用存储库模式，还使用工作单元模式。这样，您使用的每个实体都有1分。
数据/合同/ IRepository.cs
namespace Data.Contracts
{
public interface IRepository<T> where T : class
{
IQueryable<T> GetAll();
T GetById(int id);
void Add(T entity);
void Update(T entity);
void Delete(T entity);
void Delete(int id);
}
数据/合同/ IUnitOfWork.cs
namespace Data.Contracts
{
/// <summary>
/// Interface for the "Unit of Work"
/// </summary>
public interface IUnitOfWork
{
// Save pending changes to the data store.
void Commit();
// Repositories
IRepository<Event> Events { get; }
IRepository<Candidate> Candidates { get; }
}
}
数据/ EFRepository.cs
using System;
using System.Data;
using System.Data.Entity;
using System.Data.Entity.Infrastructure;
using System.Linq;
using Data.Contracts;
namespace Data
{
/// <summary>
/// The EF-dependent, generic repository for data access
/// </summary>
/// <typeparam name="T">Type of entity for this Repository.</typeparam>
public class EFRepository<T> : IRepository<T> where T : class
{
public EFRepository(DbContext dbContext)
{
if (dbContext == null)
throw new ArgumentNullException("dbContext");
DbContext = dbContext;
DbSet = DbContext.Set<T>();
}
protected DbContext DbContext { get; set; }
protected DbSet<T> DbSet { get; set; }
public virtual IQueryable<T> GetAll()
{
return DbSet;
}
public virtual T GetById(int id)
{
//return DbSet.FirstOrDefault(PredicateBuilder.GetByIdPredicate<T>(id));
return DbSet.Find(id);
}
public virtual void Add(T entity)
{
DbEntityEntry dbEntityEntry = DbContext.Entry(entity);
if (dbEntityEntry.State != EntityState.Detached)
{
dbEntityEntry.State = EntityState.Added;
}
else
{
DbSet.Add(entity);
}
}
public virtual void Update(T entity)
{
DbEntityEntry dbEntityEntry = DbContext.Entry(entity);
if (dbEntityEntry.State == EntityState.Detached)
{
DbSet.Attach(entity);
}
dbEntityEntry.State = EntityState.Modified;
}
public virtual void Delete(T entity)
{
DbEntityEntry dbEntityEntry = DbContext.Entry(entity);
if (dbEntityEntry.State != EntityState.Deleted)
{
dbEntityEntry.State = EntityState.Deleted;
}
else
{
DbSet.Attach(entity);
DbSet.Remove(entity);
}
}
public virtual void Delete(int id)
{
var entity = GetById(id);
if (entity == null) return; // not found; assume already deleted.
Delete(entity);
}
}
}
数据/ UnitOfWork.cs
using System;
using Data.Contracts;
using Data.Helpers;
using Models;
namespace Data
{
/// <summary>
/// The "Unit of Work"
/// 1) decouples the repos from the controllers
/// 2) decouples the DbContext and EF from the controllers
/// 3) manages the UoW
/// </summary>
/// <remarks>
/// This class implements the "Unit of Work" pattern in which
/// the "UoW" serves as a facade for querying and saving to the database.
/// Querying is delegated to "repositories".
/// Each repository serves as a container dedicated to a particular
/// root entity type such as a <see cref="Url"/>.
/// A repository typically exposes "Get" methods for querying and
/// will offer add, update, and delete methods if those features are supported.
/// The repositories rely on their parent UoW to provide the interface to the
/// data layer (which is the EF DbContext in this example).
/// </remarks>
public class UnitOfWork : IUnitOfWork, IDisposable
{
public UnitOfWork(IRepositoryProvider repositoryProvider)
{
CreateDbContext();
repositoryProvider.DbContext = DbContext;
RepositoryProvider = repositoryProvider;
}
// Repositories
public IRepository<Event> Events { get { return GetStandardRepo<Event>(); } }
public IRepository<Candidate> Candidates { get { return GetStandardRepo<Candidate>(); } }
/// <summary>
/// Save pending changes to the database
/// </summary>
public void Commit()
{
//System.Diagnostics.Debug.WriteLine("Committed");
DbContext.SaveChanges();
}
protected void CreateDbContext()
{
DbContext = new UnicornsContext();
}
protected IRepositoryProvider RepositoryProvider { get; set; }
private IRepository<T> GetStandardRepo<T>() where T : class
{
return RepositoryProvider.GetRepositoryForEntityType<T>();
}
private T GetRepo<T>() where T : class
{
return RepositoryProvider.GetRepository<T>();
}
private UnicornsContext DbContext { get; set; }
#region IDisposable
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (disposing)
{
if (DbContext != null)
{
DbContext.Dispose();
}
}
}
#endregion
}
}
数据/助手/ IRepositoryProvider.cs
using System;
using System.Data.Entity;
using Data.Contracts;
namespace Data.Helpers
{
/// <summary>
/// Interface for a class that can provide repositories by type.
/// The class may create the repositories dynamically if it is unable
/// to find one in its cache of repositories.
/// </summary>
/// <remarks>
/// Repositories created by this provider tend to require a <see cref="DbContext"/>
/// to retrieve data.
/// </remarks>
public interface IRepositoryProvider
{
/// <summary>
/// Get and set the <see cref="DbContext"/> with which to initialize a repository
/// if one must be created.
/// </summary>
DbContext DbContext { get; set; }
/// <summary>
/// Get an <see cref="IRepository{T}"/> for entity type, T.
/// </summary>
/// <typeparam name="T">
/// Root entity type of the <see cref="IRepository{T}"/>.
/// </typeparam>
IRepository<T> GetRepositoryForEntityType<T>() where T : class;
/// <summary>
/// Get a repository of type T.
/// </summary>
/// <typeparam name="T">
/// Type of the repository, typically a custom repository interface.
/// </typeparam>
/// <param name="factory">
/// An optional repository creation function that takes a <see cref="DbContext"/>
/// and returns a repository of T. Used if the repository must be created.
/// </param>
/// <remarks>
/// Looks for the requested repository in its cache, returning if found.
/// If not found, tries to make one with the factory, fallingback to
/// a default factory if the factory parameter is null.
/// </remarks>
T GetRepository<T>(Func<DbContext, object> factory = null) where T : class;
/// <summary>
/// Set the repository to return from this provider.
/// </summary>
/// <remarks>
/// Set a repository if you don't want this provider to create one.
/// Useful in testing and when developing without a backend
/// implementation of the object returned by a repository of type T.
/// </remarks>
void SetRepository<T>(T repository);
}
}
数据/助手/ RepositoryProvider.cs
using System;
using System.Collections.Generic;
using System.Data.Entity;
using Data.Contracts;
namespace Data.Helpers
{
/// <summary>
/// Provides an <see cref="IRepository{T}"/> for a client request.
/// </summary>
/// <remarks>
/// Caches repositories of a given type so that repositories are only created once per provider.
/// There should be a a new provider per client request.
/// </remarks>
public class RepositoryProvider : IRepositoryProvider
{
public RepositoryProvider(RepositoryFactories repositoryFactories)
{
_repositoryFactories = repositoryFactories;
Repositories = new Dictionary<Type, object>();
}
/// <summary>
/// Get and set the <see cref="DbContext"/> with which to initialize a repository
/// if one must be created.
/// </summary>
public DbContext DbContext { get; set; }
/// <summary>
/// Get or create-and-cache the default <see cref="IRepository{T}"/> for an entity of type T.
/// </summary>
/// <typeparam name="T">
/// Root entity type of the <see cref="IRepository{T}"/>.
/// </typeparam>
/// <remarks>
/// If can't find repository in cache, use a factory to create one.
/// </remarks>
public IRepository<T> GetRepositoryForEntityType<T>() where T : class
{
return GetRepository<IRepository<T>>(
_repositoryFactories.GetRepositoryFactoryForEntityType<T>());
}
/// <summary>
/// Get or create-and-cache a repository of type T.
/// </summary>
/// <typeparam name="T">
/// Type of the repository, typically a custom repository interface.
/// </typeparam>
/// <param name="factory">
/// An optional repository creation function that takes a DbContext argument
/// and returns a repository of T. Used if the repository must be created and
/// caller wants to specify the specific factory to use rather than one
/// of the injected <see cref="RepositoryFactories"/>.
/// </param>
/// <remarks>
/// Looks for the requested repository in its cache, returning if found.
/// If not found, tries to make one using <see cref="MakeRepository{T}"/>.
/// </remarks>
public virtual T GetRepository<T>(Func<DbContext, object> factory = null) where T : class
{
// Look for T dictionary cache under typeof(T).
object repoObj;
Repositories.TryGetValue(typeof(T), out repoObj);
if (repoObj != null)
{
return (T)repoObj;
}
// Not found or null; make one, add to dictionary cache, and return it.
return MakeRepository<T>(factory, DbContext);
}
/// <summary>
/// Get the dictionary of repository objects, keyed by repository type.
/// </summary>
/// <remarks>
/// Caller must know how to cast the repository object to a useful type.
/// <p>This is an extension point. You can register fully made repositories here
/// and they will be used instead of the ones this provider would otherwise create.</p>
/// </remarks>
protected Dictionary<Type, object> Repositories { get; private set; }
/// <summary>Make a repository of type T.</summary>
/// <typeparam name="T">Type of repository to make.</typeparam>
/// <param name="dbContext">
/// The <see cref="DbContext"/> with which to initialize the repository.
/// </param>
/// <param name="factory">
/// Factory with <see cref="DbContext"/> argument. Used to make the repository.
/// If null, gets factory from <see cref="_repositoryFactories"/>.
/// </param>
/// <returns></returns>
protected virtual T MakeRepository<T>(Func<DbContext, object> factory, DbContext dbContext)
{
var f = factory ?? _repositoryFactories.GetRepositoryFactory<T>();
if (f == null)
{
throw new NotImplementedException("No factory for repository type, " + typeof(T).FullName);
}
var repo = (T)f(dbContext);
Repositories[typeof(T)] = repo;
return repo;
}
/// <summary>
/// Set the repository for type T that this provider should return.
/// </summary>
/// <remarks>
/// Plug in a custom repository if you don't want this provider to create one.
/// Useful in testing and when developing without a backend
/// implementation of the object returned by a repository of type T.
/// </remarks>
public void SetRepository<T>(T repository)
{
Repositories[typeof(T)] = repository;
}
/// <summary>
/// The <see cref="RepositoryFactories"/> with which to create a new repository.
/// </summary>
/// <remarks>
/// Should be initialized by constructor injection
/// </remarks>
private RepositoryFactories _repositoryFactories;
}
}
数据/助手/ RepositoryFactories.cs
using System;
using System.Collections.Generic;
using System.Data.Entity;
using Data.Contracts;
namespace Data.Helpers
{
/// <summary>
/// A maker of Repositories.
/// </summary>
/// <remarks>
/// An instance of this class contains repository factory functions for different types.
/// Each factory function takes an EF <see cref="DbContext"/> and returns
/// a repository bound to that DbContext.
/// <para>
/// Designed to be a "Singleton", configured at web application start with
/// all of the factory functions needed to create any type of repository.
/// Should be thread-safe to use because it is configured at app start,
/// before any request for a factory, and should be immutable thereafter.
/// </para>
/// </remarks>
public class RepositoryFactories
{
/// <summary>
/// Return the runtime repository factory functions,
/// each one is a factory for a repository of a particular type.
/// </summary>
/// <remarks>
/// MODIFY THIS METHOD TO ADD CUSTOM FACTORY FUNCTIONS
/// </remarks>
private IDictionary<Type, Func<DbContext, object>> GetFactories()
{
return new Dictionary<Type, Func<DbContext, object>>
{
//If you have an custom implementation of an IRepository<T>
//{typeof(IArticleRepository), dbContext => new ArticleRepository(dbContext)}
};
}
/// <summary>
/// Constructor that initializes with runtime repository factories
/// </summary>
public RepositoryFactories()
{
_repositoryFactories = GetFactories();
}
/// <summary>
/// Constructor that initializes with an arbitrary collection of factories
/// </summary>
/// <param name="factories">
/// The repository factory functions for this instance.
/// </param>
/// <remarks>
/// This ctor is primarily useful for testing this class
/// </remarks>
public RepositoryFactories(IDictionary<Type, Func<DbContext, object>> factories)
{
_repositoryFactories = factories;
}
/// <summary>
/// Get the repository factory function for the type.
/// </summary>
/// <typeparam name="T">Type serving as the repository factory lookup key.</typeparam>
/// <returns>The repository function if found, else null.</returns>
/// <remarks>
/// The type parameter, T, is typically the repository type
/// but could be any type (e.g., an entity type)
/// </remarks>
public Func<DbContext, object> GetRepositoryFactory<T>()
{
Func<DbContext, object> factory;
_repositoryFactories.TryGetValue(typeof(T), out factory);
return factory;
}
/// <summary>
/// Get the factory for <see cref="IRepository{T}"/> where T is an entity type.
/// </summary>
/// <typeparam name="T">The root type of the repository, typically an entity type.</typeparam>
/// <returns>
/// A factory that creates the <see cref="IRepository{T}"/>, given an EF <see cref="DbContext"/>.
/// </returns>
/// <remarks>
/// Looks first for a custom factory in <see cref="_repositoryFactories"/>.
/// If not, falls back to the <see cref="DefaultEntityRepositoryFactory{T}"/>.
/// You can substitute an alternative factory for the default one by adding
/// a repository factory for type "T" to <see cref="_repositoryFactories"/>.
/// </remarks>
public Func<DbContext, object> GetRepositoryFactoryForEntityType<T>() where T : class
{
return GetRepositoryFactory<T>() ?? DefaultEntityRepositoryFactory<T>();
}
/// <summary>
/// Default factory for a <see cref="IRepository{T}"/> where T is an entity.
/// </summary>
/// <typeparam name="T">Type of the repository's root entity</typeparam>
protected virtual Func<DbContext, object> DefaultEntityRepositoryFactory<T>() where T : class
{
return dbContext => new EFRepository<T>(dbContext);
}
/// <summary>
/// Get the dictionary of repository factory functions.
/// </summary>
/// <remarks>
/// A dictionary key is a System.Type, typically a repository type.
/// A value is a repository factory function
/// that takes a <see cref="DbContext"/> argument and returns
/// a repository object. Caller must know how to cast it.
/// </remarks>
private readonly IDictionary<Type, Func<DbContext, object>> _repositoryFactories;
}
}
现在，如果您使用UnitOfWork，则不能简单地调用它，因为所有依赖项，如果您在知道可以简单地解决这些依赖项之前使用了IoC容器。在我的情况下，我使用了Ninject，因此设置它的代码将是：
var kernel = new StandardKernel(); // Ninject IoC
kernel.Bind<RepositoryFactories>().To<RepositoryFactories>().InSingletonScope();
kernel.Bind<IRepositoryProvider>().To<RepositoryProvider>();
kernel.Bind<IUnitOfWork>().To<UnitOfWork>();
然后，对于您的页面，您可以添加基页类：
<强> Web.BasePage.cs
namespace Web
{
public abstract class BasePage : System.Web.UI.Page
{
// NOT NECESSARY TO DISPOSE THE UOW IN OUR CONTROLLERS
// Recall that we let IoC inject the Uow into our controllers
// We can depend upon on IoC to dispose the UoW for us
protected IUnitOfWork Uow { get; set; }
}
}
或者在MVC的情况下，你可以添加一个基本控制器：
网络/控制器/ BaseController.cs
using System.Web.Mvc;
namespace Site.Controllers
{
public abstract class BaseController : Controller
{
// NOT NECESSARY TO DISPOSE THE UOW IN OUR CONTROLLERS
// Recall that we let IoC inject the Uow into our controllers
// We can depend upon on IoC to dispose the UoW for us
protected IUnitOfWork Uow { get; set; }
}
}
然后在您的代码中，当您想要访问实体时，它非常容易。您只需调用每个页面中可用的UnitOfWork并访问其中的不同存储库即可。因为它们都共享相同的DbContext，所以问题就不复存在了。
我已经制作了一个非常简单的工作单元模式示例，并支持Ninject控制反转。
在我的示例中，有一个 ASP.NET Webforms AND 和ASP.NET MVC4 示例
该示例是一个单页面站点，每次加载站点时，它都会向示例数据库添加一个事件，并将数据库的类别添加到数据库中，两者都是随机名称。 （我需要DB的东西所以我只做了两个简单的pocos）。之后，页面将显示两个列表中的所有内容。只需查看Mvc4/Controllers/HomeController.cs或WebForms/Default.aspx.cs。
答案 1 :(得分：1)
当您尝试更新的实体附加到与您用于更新它的上下文不同的objectcontext时，确实会抛出此错误。只有一个objectcontext可以跟踪实体
您可以通过调用：
从其上下文中分离对象其中context是实体当前所附加的上下文。
using (var context = new UnicornsContext())
{
var unicorn = new Unicorn { Name = "Franky", PrincessId = 1};
context.Entry(unicorn).State = EntityState.Detached;
context.SaveChanges();
}
在您的实施中：
public void UpdateAddingCandidate(Event eventObj, Candidate candidate)
{
db.Entry(candidate).State = EntityState.Detached;
db.SaveChanges();
eventObj.Candidate = candidate;
db.Entry(eventObj).State = EntityState.Modified;
db.SaveChanges();
}
答案 2 :(得分：0)
为什么要创建Event和Candidate的新实例？你可以改变你已经拥有它们的状态。如果您在您的存储库中共享相同的ObjectContext实例，则可以尝试使用ObjectStateManager.GetObjectStateEntry(string key) ObjectStateManager从上下文中解析这些实体。