Entity Framework 4.1 Codefirst: "Given the limitations of multiplicity" error when deleting one-to-many children

Question

I have the following classes in Entity Framework 4.1 (classes were cropped to read code)

public class MetaInformation { public int Id { get; set; } public virtual MetaInformationObject RelatedTo { get; set; } } public abstract class MetaInformationObject { public int Id { get; set; } public virtual List<MetaInformation> MetaInformations { get; set; } } [Table("Hardwares")] public class Hardware : MetaInformationObject { [MaxLength(100)] public string Name { get; set; } } public class Inventory { public int Id { get; set; } public virtual List<Machine> Machines { get; set; } } public class Machine : Hardware { public Inventory Inventory { get; set; } } protected override void OnModelCreating(DbModelBuilder modelBuilder) { modelBuilder.Entity<Isis.Business.Base.MetaInformationObject>() .HasMany<Isis.Business.Base.MetaInformation>(mi => mi.MetaInformations).WithRequired(mi => mi.RelatedTo).WillCascadeOnDelete(true); modelBuilder.Entity<Isis.Business.Inventory.Inventory>() .HasMany<Isis.Business.Inventory.Machine>(i => i.Machines).WithRequired(m => m.Inventory).WillCascadeOnDelete(true); base.OnModelCreating(modelBuilder); } 

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At some point, I would like to update the information about the machine, so if it already exists in the database, I load it, attach it, and then clear the previous meta information to replace it with new ones.

 public void UpdateMachine(Inventory i, Machine m) { DataContext.Dao.Db.Inventories.Attach(i); if (!i.Machines.Exists(InnerHardware => InnerHardware.SerialNumber == m.SerialNumber)) { i.Machines.Add(m); } else { var workingMachine = i.Machines.First(Machine => Machine.SerialNumber == m.SerialNumber); Dao.Db.Machines.Attach(workingMachine); if (workingMachine.MetaInformations != null && workingMachine.MetaInformations.Count > 0) { workingMachine.MetaInformations.Clear(); //workingMachine.MetaInformations.ForEach(mi => { Dao.Db.MetaInformations.Attach(mi); Dao.Db.MetaInformations.Remove(mi); }); // tried this to, with variations } workingMachine.MetaInformations = m.MetaInformations; } DataContext.Dao.Db.SaveChanges(); } 

And then the following DbUpdateException is thrown:

Relations from 'MetaInformationObject_MetaInformations' AssociationSet is in the Deleted state. Given the multiplicity of constraints corresponding to 'MetaInformationObject_MetaInformations_Target' should also be in the Deleted State.

I tried to answer some questions here to solve the problem, especially trying to read this and the link provided in the answer (which is the reason there is a direct link from MetaInformation to MetaInformationObject ), but I can not understand what is wrong.

Answer 1

Cascade delete will not help you here. Cascade delete only works when deleting the parent object ( MetaInformationObject ). The problem here is that calling Clear on a collection of related objects does not delete them. It only removes the relation (= it will set the foreign key in MetaInformation to null), but it is not allowed by the display constraints (if necessary, you define the relation). Ways to avoid this:

• Iterate through all related MetaInformation and delete each one
• The refactoring that you model to determine the relationship identification . After that, Clear will not only break the connection, but also mark the associated object as deleted.

Answer 2

Repeating the above comment, the code below will solve your problem

DataContext.Dao.Db.MetaInformations.RemoveRange (workingMachine.MetaInformations);