RemoveRange抛出InvalidOperationException异常实体框架的核心

Question

我得到的错误：

The instance of entity type 'Pupil' cannot be tracked because another instance of this type with the same key is already being tracked. When adding new entities, for most key types a unique temporary key value will be created if no key is set (i.e. if the key property is assigned the default value for its type). If you are explicitly setting key values for new entities, ensure they do not collide with existing entities or temporary values generated for other new entities. When attaching existing entities, ensure that only one entity instance with a given key value is attached to the context.

我能明白这一点错误，如果我想这种情况下，然后在上下文高速缓存加载之前已经恢复，但我haven`t！ ！

var pupilsToDelete = pupilIds.Select(id => new Pupil { Id = id }); 
    context.RemoveRange(pupilsToDelete.ToList()); 
    await context.SaveChangesAsync(); 

运行期间pupilIds都是不同的ID！

为什么我得到那个错误？

Answer 1

删除记录需要从上下文进行跟踪。因此，而不是创造新Pupil收集从上下文

var pupilsToDelete = context.Pupils.Where(a => pupilIds.Contains(a.Id)).Select(b => b); 
context.Pupils.RemoveRange(pupilsToDelete); 
await context.SaveChangesAsync(); 

Answer 2

只是引用它们要能够删除记录，你需要确保你的ObjectContext的是跟踪他们。删除项目的最佳方法是由@Mostafiz回答，但您也可以将您的实体附加到上下文。

var pupilsToDelete = pupilIds.Select(id => new Pupil { Id = id }); 
foreach(var p in pupilsToDelete) 
    context.Attach(p); 
context.RemoveRange(pupilsToDelete.ToList()); 
await context.SaveChangesAsync(); 

哪个不好办法。