实体框架链表

Question

我有一个实体(我首先使用代码)看起来像这样:

public class Node
{
    public int ID { get; set; }
    public string SomeInfo { get; set; }

    public virtual Node Previous { get; set; }
    public virtual Node Next { get; set; }
}

例如,保存Next Node没有问题.但是,如果Previous的ID为1,并且我尝试将Next Node(ID为1的那个)设置为2,则抛出此异常.

无法将对象添加到对象上下文中.object sEntityKey有一个ObjectStateEntry,指示对象已经参与了不同的关系.

我正在保存这样的节点:

int nextId;
int previousId;
if (int.TryParse(Request["previous"], out previousId))
   node.Previous = this.nodeRepository.GetSingle(previousId);

if (int.TryParse(Request["next"], out nextId))
   node.Next = this.nodeRepository.GetSingle(nextId);

this.nodeRepository.Update(node);

更新如下所示:

public virtual void Update(T entity)
{
    this.context.Entry(GetSingle(entity.ID)).State = EntityState.Detached;
    this.context.Entry(entity).State = EntityState.Added;
    this.context.Entry(entity).State = EntityState.Modified;

    this.Save();
}

和GetSingle这样:

public virtual T GetSingle(object id)
{
    var query = this.entities.Find(id);
    return query;
}

更新1

具有异常的行在Update方法中:

this.context.Entry(entity).State = EntityState.Modified;

Answer 1

您的上下文是否位于 using 块中并在某个时刻被丢弃？我遇到过类似的“无法将对象添加到对象上下文中。”错误。我会将“上一个”和“下一个”的 Id 添加到模型中，并使用它们来更新外键。

public class Node
{
    public int ID { get; set; }
    public string SomeInfo { get; set; }

    public virtual Node Previous { get; set; }
    public int PreviousId { get; set; }
    public virtual Node Next { get; set; }
    public int NextId { get; set; }
}

要更新外键...

int nodeId;  // I'm assuming you know the id of node you want updated.

int nextId;
int previousId;


using (var context = new Context()) 
{     
    // Perform data access using the context 
    var node = context.Nodes.find(nodeId);
    node.NextId = nextId;
    node.PreviousId = previousId;
    context.SaveChanges();
}