清除FK时删除EF中的实体

Question

Use the following model as an example:

public class Item
{
    public int ItemId { get; set; }
    public int? ScanId { get; set; }
    public Scan Scan { get; set; }
}

public class Scan
{
    public int ScanId { get; set; }
}

Let's say I've associated an instance of Scan to an instance of Item . If I disassociate the Scan record, I want to know if there is a way to configure EF such that it would automatically delete the orphaned Scan record. I believe the concept of cascading deletes does not apply to this situation because it would only pertain to deleting a Scan record if it's Item record was deleted.

Thanks in advance.

Answer 1

How about overriding SaveChanges() ? You could check for the modified Item entities, check whether originally the ScanId was not null and now it is null, get the Scan entity for the original ScanId, and then remove it. Something like this:

 public override int SaveChanges()
 {
   List<int> orphanedScanIds = new List<int>();
   foreach (var item in this.ChangeTracker.Entries().Where(e => e.Entity is Item && e.State == EntityState.Modified))
   {
      var original = (int?)item.OriginalValues[nameof(Item.ScanId)];
      var current = (int?)item.CurrentValues[nameof(Item.ScanId)];
      if (original.HasValue && !current.HasValue)
      {
          orphanedScans.Add(original.Value);
      }
   }
   var orphanedScans = this.Scans.Where(s => orphanedScans.Contains(s.ScanId)).ToList();
   foreach (var orphanedScan in orphanedScans)
   {
      this.Scans.Remove(orphanedScan);
   }
   return base.SaveChanges();
 }