實體框架如何正確更新一個實體代碼？

Question

我在通用存儲庫下面的更新方法

public class Repository<T> : IRepository<T> where T : class 
{ 
    private readonly DbSet<T> _dbSet; 
    public virtual T Update(T item) { 
     return _dbSet.Attach(item); 
    } 
} 

的UnitOfWork有其呼籲的背景下SaveChanges提交方法。更多細節在這裏
https://codereview.stackexchange.com/questions/19037/entity-framework-generic-repository-pattern

當我更新的實體，然後調用

ProductRepository.Update(modifiedProduct); 
UnitOfWork.Commit; 

沒有飄下來到數據庫。

但是，僅僅調用提交工程（沒有調用更新方法）。

那麼，Attach Method是什麼導致更改不會流到數據庫。 我認爲附加調用是在更新方法中進行的正確調用。那麼，是什麼導致了意外的行爲。

從EF的源代碼在CodePlex上

/// <summary> 
///  Attaches the given entity to the context underlying the set. That is, the entity is placed 
///  into the context in the Unchanged state, just as if it had been read from the database. 
/// </summary> 
/// <param name="entity"> The entity to attach. </param> 
/// <returns> The entity. </returns> 
/// <remarks> 
///  Attach is used to repopulate a context with an entity that is known to already exist in the database. 
///  SaveChanges will therefore not attempt to insert an attached entity into the database because 
///  it is assumed to already be there. 
///  Note that entities that are already in the context in some other state will have their state set 
///  to Unchanged. Attach is a no-op if the entity is already in the context in the Unchanged state. 
/// </remarks> 
public object Attach(object entity) 
{ 
    Check.NotNull(entity, "entity"); 

    InternalSet.Attach(entity); 
    return entity; 
} 

Answer 1

///  Attach is used to repopulate a context with an entity that is known to already exist in the database. 
///  SaveChanges will therefore not attempt to insert an attached entity into the database because 
///  it is assumed to already be there. 
///  Note that entities that are already in the context in some other state will have their state set 
///  to Unchanged. 

連接實體後，國家將保持不變，因此沒有更新SQL是要觸發該實體。連接後您需要手動設置實體的狀態。

Answer 2

您需要將對象附加爲modified或added以生成對數據庫的查詢。

public virtual T AttachAsModified(T item) { 
     item = _dbSet.Attach(item); 
     db.Entry(item).State = System.Data.EntityState.Modified 
     return item; 
    }