与实体框架级联删除

Question

I have a comments table which contains amongst other things the columns Id - the ID of the comment, Commenter_Id the ID of the user who posted it, and ParentComment_Id a self referencing foreign key. There are only two levels to the commenting, parents and sub comments. If a comment record has a ParentComment_Id of null, then it is a parent comment.

I'm trying to write an expression to delete all the comments for a user, but this is causing problems because of that self reference I mentioned earlier.

Take this records sample as an example of the problem:

User with ID 2 posted a comment, with an ID of 3. Because this was the parent comment it has a ParentComment_Id value of null. Later on, User with ID 1 responds to that comment with a sub-comment, creating comment 7 (there were other comments/subcomments between these two hence the Id increment jump).

I'm not able to delete Comment ID 3 because the sub comment, Comment ID 7, has a foreign key to it.

Currently my Entity Framework statement for trying to delete comments is as follows:

context.Comments.Where(x => x.Commenter.Id == user.Id).Delete();

But this gives me an exception because of the described problem.

I could probably fix this using a few foreach loops, but I was hoping there is an easier way like context.Cascade().Where(... . For those wondering the Delete() method is part of the EntityFramework.Extended package.

Answer 1

If you have an entity like this:

public class Comment
{
  public int Id{get;set;}
  public int? ParentCommentId{get;set;}

  public virtual Comment ParentComment{get;set;}
  public virtual ICollection<Comment> Comments{get;set;}
}

You could try with this configuration:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Entity<Comment>()
                .HasOptional(c=>c.ParentComment)
                .WithMany(c=>c.Comments)
                .HasForeignKey(c => c.ParentCommentId) 
                .WillCascadeOnDelete(true);
}

You can configure cascade delete on a relationship by using the WillCascadeOnDelete method.If a foreign key on the dependent entity is nullable , Code First does not set cascade delete on the relationship , and when the principal is deleted the foreign key will be set to null.

Answer 2

You can try adding this to your dbcontext

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Entity<Comments>()
                .HasForeignKey(d => d.ParentCommentId) 
                .WillCascadeOnDelete(true);
}