Multiplicity error when generating database from model? - mapping

Question

have 3 classes:
public class User
{
public Guid Id { get; set; }
public string Username { get; set; }
public string PersonelNumber { get; set; }
public string Password { get; set; }
public bool IsActive { get; set; }
public DateTime LastLoginDate { get; set; }
public bool IsOnline { get; set; }
}
public class Comment
{
public Guid Id { get; set; }
/// <summary>
/// Title of the comment
/// </summary>
public string Title { get; set; }
/// <summary>
/// Full text for comment
/// </summary>
public string Text { get; set; }
//Maps to the User Id
public Guid CreatedById { get; set; }
public virtual User CreatedBy { get; set; }
}
public class FileVersion
{
public Guid Id { get; set; }
public string Path { get; set; }
public int Version { get; set; }
//Referecne to optional comment
public virtual Guid ChangeCommentId { get; set; }
public virtual Comment ChangeComment { get; set; }
//Referece to user who added a file
public virtual Guid AddedById { get; set; }
public virtual User AdddedBy { get; set; }
//Reference to User who may have the file checked out
public virtual Guid CheckedOutById { get; set; }
public virtual User CheckedOutBy { get; set; }
}
I am receiving the error when the database tries to create the Comment relationship between FilVersion and Comment. I did create this mapping for the FileVersion class:
HasOptional(f => f.ChangeComment).WithMany().HasForeignKey(f => f.ChangeCommentId).WillCascadeOnDelete(false);
I am not sure how to setup my mappings so that I do not get the Multiplicity error when the database is created. The FileVersion needs a referecne to who added the file and who may have it checkedout for edit.

Answer 1

The problem is that you cannot define Comment as optional when the foreign key doesn't accept null. Either modify your entity to:
public class FileVersion
{
...
public virtual Guid? ChangeCommentId { get; set; }
public virtual Comment ChangeComment { get; set; }
...
}
Or modify your mapping to:
modelBuilder.Entity<FileVersion>()
.HasRequired(f => f.ChangeComment)
.WithMany()
.HasForeignKey(f => f.ChangeCommentId)
.WillCascadeOnDelete(false);
Same will be probably needed for CheckedOutBy