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我的通用存储库中有以下更新方法

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

有一个在上下文UnitOfWork中调用的提交方法。SaveChanges更多细节在这里
https://codereview.stackexchange.com/questions/19037/entity-framework-generic-repository-pattern

当我更新实体然后调用

ProductRepository.Update(modifiedProduct);
UnitOfWork.Commit;

没有任何东西飘到数据库中。

但是，仅调用 Commit 即可（不调用更新方法）。

那么，附加方法的作用是什么导致更改不会向下流入数据库。我认为附加调用是在更新方法中进行的正确调用。那么，是什么导致了意外行为。

来自 CodePlex 上的 EF 源代码

/// <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;
}
4

2 回答 2

5 
///     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.

附加实体后，状态将保持不变，因此不会为该实体触发 UPDATE sql。您需要在附加后手动设置实体的状态。

于 2012-12-19T09:33:17.663 回答
4

您需要将对象附加为modified或added生成对数据库的查询。

  public virtual T AttachAsModified(T item) {
        item = _dbSet.Attach(item);
        db.Entry(item).State = System.Data.EntityState.Modified
        return item;
    }
于 2012-12-19T09:34:14.207 回答