Question

While adding post to the post repository an exception occurs with the following message: not null property references a null or transient value Category.

[Test]
public void PostInsertion()
{
    var category = new Category 
    {
        Title = "Programming",
        Description = "Programming"
    };
    var post = new Post
    {
        AuthorUrl = "some url",
        Category = category,
        Content = "some content",
        Feedbacks = new HashedSet<Feedback>(),
        Timestamp = DateTime.Now,
        Title = "some title"
    };

    var postRepository = new Repository<Post>(this.sessionFactory);
    postRepository.Add(post);
}

What does it mean?

EDIT: Post entity definition

[Serializable]
public class Post : Entity<Post>
{
    public Post()
    {
        this.Feedbacks = new HashedSet<Feedback>();
    }

    public virtual String Title { get; set; }
    public virtual String Content { get; set; }
    public virtual DateTime Timestamp { get; set; }
    public virtual Byte[] Thumbnail { get; set; }
    public virtual Byte[] AuthorImg { get; set; }
    public virtual String AuthorUrl { get; set; }
    public virtual Category Category { get; set; }
    public virtual ISet<Feedback> Feedbacks { get; set; }

    public virtual void AddFeedback(Feedback feedback)
    {
        this.Feedbacks.Add(feedback);
    }
}

Thanks!

Answer 1

That exception was thrown because NHibernate tried to add a reference to a Category that was not persisted on the database. In you example you are creating a new Category, so you have two options:

1. Save the Category before saving the Post;
2. Change the Post mapping and make it cascade save the associations;

For the second option, if you are using Xml mapping, then you’ll need something like:

<many-to-one name="Category" column="CategoryId" cascade="all"/>

If you are using Fluent NHibernate, then it’ll be:

References(x => x.Category, "CategoryId").Cascade.All();