c# - Entity Framework 中的递归实体分离

我编写了一种方法来递归分离实体框架中的对象。实际上它是可行的，但问题是执行此方法后，一对多属性（对象的Collections）将被删除。在我的代码下方：

public void DetachRec(object objectToDetach)
{
  DetachRec(objectToDetach, new HashSet<object>());
}

// context is my ObjectContext
private void DetachRec(object objectToDetach, HashSet<object> visitedObjects)
{
  visitedObjects.Add(objectToDetach);

  if (objectToDetach == null)
  {
    return;
  }
  Type type = objectToDetach.GetType();
  PropertyInfo[] propertyInfos = type.GetProperties();
  foreach (PropertyInfo propertyInfo in propertyInfos)
  {
    // on to many
    if (propertyInfo.PropertyType.IsGenericType && propertyInfo.PropertyType.GetGenericTypeDefinition() == typeof(ICollection<>))
    {

      if (context.Entry(objectToDetach).Collection(propertyInfo.Name).IsLoaded)
      {

        var propValue = (IEnumerable) propertyInfo.GetValue(objectToDetach, null);

        if (propValue != null)
        {
          var subcontext = new List<object>();

          foreach (var subObject in propValue)
          {
            subcontext.Add(subObject);
          }
          foreach (var subObject in subcontext)
          {
            if (!visitedObjects.Contains(subObject))
            {
              context.DetachRecursive(subObject, visitedObjects);
            }
          }
        }
      }
    }
    // (many to one)
    else if (propertyInfo.PropertyType.Assembly == type.Assembly)
    {
        //the part to detach many-to-one objects
    }
  }

  context.Detach(objectToDetach);
}

最佳答案

在分离收集元素之前，您可以存储收集值并将收集属性设置为null。这样，当元素和/或父实体分离时，您将防止EF删除集合元素。在该过程结束时，您只需将这些值恢复回来。

首先将以下using添加到源代码文件：

using System.Data.Entity.Infrastructure;

更改公共方法的实现，如下所示：

public void DetachRec(object objectToDetach)
{
    var visitedObjects = new HashSet<object>();
    var collectionsToRestore = new List<Tuple<DbCollectionEntry, object>>();
    DetachRec(objectToDetach, visitedObjects, collectionsToRestore);
    foreach (var item in collectionsToRestore)
        item.Item1.CurrentValue = item.Item2;
}

私有递归方法签名可以：

private void DetachRec(object objectToDetach, HashSet<object> visitedObjects, List<DbCollectionEntry, object>> collectionsToRestore)

一对多if块主体可以：

var collectionEntry = context.Entry(objectToDetach).Collection(propertyInfo.Name);
if (collectionEntry.IsLoaded)
{
    var collection = collectionEntry.CurrentValue;
    if (collection != null)
    {
        collectionsToRestore.Add(Tuple.Create(collectionEntry, collection));
        collectionEntry.CurrentValue = null;
        foreach (var item in (IEnumerable)collection)
        {
            if (!visitedObjects.Contains(item))
            {
                DetachRec(item, visitedObjects, collectionsToRestore);
            }
        }
    }
}

到此为止。

关于c# - Entity Framework 中的递归实体分离，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/43146332/