Question

I have ran into quite an interesting mapping scenario. I have two entities (Task and ProjectEmployeeFile) that has two identical foreign keys (ProjectId and EmployeeId).

I am trying to find an elegant way to map a Tasks property to the ProjectEmployeeFile entity.

I think that the solution for one foreign key relationship would be by using a ternary association but I have no idea how to project this into multiple foreign keys.

I am using fluent nhibernate but if solving this issue with classic hbm files is the way to go I have no problem with mapping those classes manually.

Any help would be greatly appreciated.

I have drawn a basic diagram to try to illustrate the scenario:

I have mixed property names with database column names freely here but I think the general idea is clear.

update

In order to clarify the domain model, here is the current entities and mappings, stripped to the minimum:

    public class Task
    {
        public virtual int Id { get; private set; }
        public virtual Project Project { get; set; }
        public virtual Employee Employee { get; set; }
    }

    public class ProjectEmployeeFile
    {
        public virtual int Id { get; private set; }
        public virtual Project Project { get; set; }
        public virtual Employee Employee { get; set; }
    }

    public class Project
    {
        public virtual int Id { get; private set; }
        public virtual IList<Task> Tasks { get; set; }

    }

    public class Employee
    {
        public virtual int Id { get; private set; }
        public virtual IList<Task> Tasks { get; set; }
    }


public class TaskMap : ClassMap<Task>
{
    public TaskMap()
    {
        Table("Tasks");
        Id(x => x.Id);
        References(x => x.Project).Column("ProjectId");
        References(x => x.Employee).Column("EmployeeId");
    }
}

public class ProjectEmployeeFileMap : ClassMap<ProjectEmployeeFile>
{
    public ProjectEmployeeFileMap()
    {
        Table("ProjectEmployeeFiles");
        Id(x => x.Id);
        References(x => x.Project).Column("ProjectId");
        References(x => x.Employee).Column("EmployeeId");
    }
}

Answer 1

This mapping might work (I haven’t tested it):

<class name="ProjectEmployeeFile">
  ...
  <bag name="Tasks" inverse="true">
    <key column="ProjectId" property-ref="Project"/>
    <key column="EmployeeId" property-ref="Employee"/>
    <one-to-many class="Task"/>
  </bag>
</class>

I don’t know if it’s possible to do it with fluent, but you can mix them anyway.