由于跟踪问题，添加后无法删除项目

Question

I am adding an entity using the Upsert method below and deleting it after using the Delete method.

However this throws on the this.Items.Remove(item) line with the below error.

public async Task<TEntity> Upsert(TEntity item)
{
   var entity = this.Context.Update(item);
   await this.SaveChangesAsync();
   return entity.Entity;
}

public async Task Delete(TEntity item)
{
   this.Items.Remove(item);
   await this.SaveChangesAsync();
}

Error:

The instance of entity type 'x' cannot be tracked because another instance with the key value '{Id: 204}' is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached.

I think the issue here is that, when I add an entity, it is added as tracked and when I try to delete, it can't be deleted while being tracked?

Any help vastly appreciated, I'm still new to Entity Framework.

Answer 1

If you Edit or Remove an record form DataBase , the ChaneTracker change the state of entity to Modified or Removed In Current Context , And if you read the data from the database ( In Current Context ), because the entities are tracked by ChangeTracker an error occurs because in the ChangeTracker can't exist two record with a key at the same time. so you must clear tracked entities from ChangeTracker .

Add this code after await this.SaveChangesAsync();to detach records from ChangeTracker

foreach (var entity in this.Context.ChangeTracker.Entries())
{
     entity.State = System.Data.Entity.EntityState.Detached;
}