Question

When I test my many to many classes an error occurs:

System.ApplicationException: Actual count does not equal expected count.

Entities:

    public interface IEntity
    {
        int Id { get; set; }
    }

    public abstract class Entity : IEntity
    {
        public virtual int Id { get; set; }

        public virtual bool IsPersistent
        {
            get { return isPersistentObject(); }
        }

        public override bool Equals(object obj)
        {
            if (isPersistentObject())
            {
                var persistentObject = obj as Entity;
                return (persistentObject != null) && (Id == persistentObject.Id);
            }

            return base.Equals(obj);
        }

        public override int GetHashCode()
        {
            return isPersistentObject() ? Id.GetHashCode() : base.GetHashCode();
        }

        private bool isPersistentObject()
        {
            return (Id != 0);
        }
    }

    public class Team : Entity
    {
        public virtual string Name { get; set; }
        public virtual ISet<Employee> Employees { get; set; }

        public Team()
        {
            Employees = new HashedSet<Employee>();
        }
    }

    public class Employee : Entity
    {
        public virtual string LastName { get; set; }
        public virtual string FirstName { get; set; }
        public virtual ISet<Team> Teams { get; set; }
        public virtual string EMail { get; set; }

        public Employee()
        {
            Teams = new HashedSet<Team>();
        }
    }

Mappings:

public class TeamMap : ClassMap<Team>
{
    public TeamMap()
    {
        // identity mapping
        Id(p => p.Id).Column("TeamID");

        // column mapping
        Map(p => p.Name);

        // relationship mapping
        HasManyToMany(m => m.Employees)
            .Table("EmployeeTeam")
            .LazyLoad()
            .Cascade.SaveUpdate()
            .AsSet()
            .ParentKeyColumn("TeamID")
            .ChildKeyColumn("EmployeeID");
    }
}

public class EmployeeMap : ClassMap<Employee>
{
    public EmployeeMap()
    {
        // identifier mapping
        Id(p => p.Id).Column("EmployeeID");

        // column mapping
        Map(p => p.EMail);
        Map(p => p.LastName);
        Map(p => p.FirstName);

        // relationship mapping
        HasManyToMany(m => m.Teams).Table("EmployeeTeam")
            .Inverse()
            .Cascade.SaveUpdate()
            .AsSet()
            .LazyLoad()
            .ParentKeyColumn("EmployeeID")
            .ChildKeyColumn("TeamID");
    }
}

Test:

[TestMethod]
public  void  CanCorrectlyMapEmployee()
{
    var team = new List<Team> {new Team() {Name = "Team1"}};

    new PersistenceSpecification<Employee>(_session)
        .CheckProperty(p => p.EMail, "Mail")
        .CheckProperty(p => p.FirstName, "Firstname")
        .CheckProperty(p => p.Id, 1)
        .CheckProperty(p => p.LastName, "Lastname")
        .CheckList(p => p.Teams,team )
        .VerifyTheMappings();
}

Whether I add an Employee or a Team my EmployeeTeam table is always empty.

I have tested it against SQLLite with FNH and manually against SQL Server 2008.

Does anybody of you have an idea to fix this?

edit:

I was amazed to find out that when I create an Employee and add 2 Teams to the Employee and load the created Employee he has 2 Teams. So it works fine. But when I look in my relationsip table EmployeeTeam then everything is empty. Can someone explain me why?

And does anybody know how I can use Fluent NHibernate to test my many to many relationship?

Thanks in advance!

Answer 1

Employee map has inverse attribute. As you probably know, this means that when you save employee, relationship table (EmployeeTeam) will not be updated. To add/remove new relationship information you have to add employee to the Team and save Team.

So, in your case - don t test many to many on the side of employee, test it on the side of team. (If you d like NHibernate to add records when you add team to employee, you ll have to invert "Inverse" attributes - give it to team, not employee, but then - same story with Team entity).

Why were you able to load Employee with teams? Because of session-level cache. You ve probably saved and loaded Employee in the same ISession - this means that NHibernate returned you exactly reference to the same object, without loading it from the db. Try saving & loading in two different sessions and you ll see no team in Employee.Teams set.

Side note: It is considered a good practice to create methods that will enforce consistency between many-to-many relationships, that is - when you add Team to Employee, Employee is added to the team, sth. like this:

class Employee 
{
  // ...
  public void AddTeam(Team team)
  {
     // check for null, etc. 

     Teams.Add(team);
     team.Employees.Add(this);
  }
}

and very simillar method in the Team class.

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