CompositeId() throws exception - Could not compile the mapping document: (XmlDocument)

After defining a map for composite key

 CompositeId()
                .KeyProperty(x => x.title)
                .KeyProperty(x => x.label);

The following exception is raised when trying to create a composite key

CreateSessionFactory() - Inner exception: An invalid or incomplete configuration was used while creating a SessionFactory. Check PotentialReasons collection, and InnerException for more detail.
..
CreateSessionFactory() - Inner exception: Could not compile the mapping document: (XmlDocument)
CreateSessionFactory() - Inner exception: composite-id class must override Equals(): CSharpTechies.Data.Entities.post

This means "post" entity definition should override at least 2 members GetHashCode() and Equals(object obj) Now here is how code snippet looks

public override int GetHashCode()
{
 int hashCode = 0;
 hashCode = hashCode ^ title.GetHashCode() ^ label.GetHashCode();
 return hashCode;
}

public override bool Equals(object obj)
{
 var toCompare = obj as post;
 if (toCompare == null)
 {
  return false;
 }
 return (this.GetHashCode() != toCompare.GetHashCode());
} 

Remember if the entity "post" is referenced elsewhere (ie.. foreign key) then you might get some more exceptions

CreateSessionFactory() - caught EXCEPTION: An invalid or incomplete configuration was used while creating a SessionFactory. Check PotentialReasons collection, and InnerException for more detail.
..
CreateSessionFactory() - Inner exception: Foreign key (FK36342426872A80CB:AuthorPosts [Post_id])) must have same number of columns as the referenced primary key (Post[title, label])

So update reference mapping as

  References(x => x.Post)
                .Columns(new string[] { "title", "label" })
                .Not.Update()
                .Not.Insert();

or one-to-many mapping as

 HasMany(x => x.Posts)
                .KeyColumns.Add("title")
                .KeyColumns.Add("label")
                .Not.LazyLoad()
                .Inverse();

“We have to stop optimizing for programmers and start optimizing for users.” – Jeff Atwood