entity-framework - Entity Framework 链表

Question

我有一个看起来像这样的实体(我首先使用代码):

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; }
}

例如保存下一个节点没有问题。但是，如果上一个的 ID 为 1 并且我尝试将下一个节点(即 ID=1 的节点)设置为 2，则会引发此异常。

The object cannot be added to the object context. The object�s EntityKey has an ObjectStateEntry that indicates that the object is already participating in a different relationship.

我正在像这样保存节点:

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);

更新看起来像这样:

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 像这样:

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

更新 1

有异常(exception)的行在 Update 方法中:

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

Answer 1

您的上下文是否在 Using 块中并在某个时候被处理？我有类似的“对象无法添加到对象上下文。”错误。我会将上一个和下一个的 Id 添加到您的模型中，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();
}