Question

I know there are several questions regarding this topic. However; I cannot find one that is directly related to my problem.

I have 3tables in a DB and the PK’s from those 3 tables form a composite PK in a XRef table.

I need to be able to select Distinct items based on 2 of the keys just for display on a report.

    public IEnumerable<AssemblyPrograms> GetProgramAssemblies()
    {
        var assembliesList = (from c in eModel.Assemblies.ToList()
                             join d in eModel.Programs_X_Assemblies_X_Builds
                             on c.AssemblyID equals d.AssemblyID
                             join p in eModel.Programs
                             on d.ProgramID equals p.ProgramID
                             join a in eModel.AssemblyTypes
                             on c.AssemblyTypeID equals a.AssemblyTypeID

                             select new AssemblyPrograms
                             {
                                 AssemblyID = c.AssemblyID
                                 ,ProgramID = d.ProgramID
                                 ,AssemblyName = c.AssemblyName
                                 ,AssemblyPrefixName = c.AssemblyPrefixName
                                 ,ProgramName = p.ProgramName
                                 ,AssemblyTypeName = a.AssemblyTypeName
                                 ,AssemblyTypeID = a.AssemblyTypeID
                             });

        return assembliesList;
    }

This is my query and what I need to pull out of the tables

In my XRef table I have AssemblyID, ProgramID and BuildID as my composite PK.

There can be a many-many relationship from AssemblyID to ProgramID. The BuildID is the key that separates them.

I need to pull Distinct AssemblyID to ProgramID relationships for my report, the BuildID can be ignored.

I have tried .Distinct() in my query and a few other things to no avail.

I would appreciate any help anyone could give me.

Thanks

Answer 1

How about a Distinct overload that accepts a custom equality comparer? Something like this:

class AssemblyComparer : EqualityComparer<AssemblyPrograms> {
    public override bool Equals(AssemblyPrograms x, AssemblyPrograms y) {
        return x.ProgramID == y.ProgramID && x.AssemblyID == y.AssemblyID;
    }

    public override int GetHashCode(AssemblyPrograms obj) {
        return obj.ProgramID.GetHashCode() ^ obj.AssemblyID.GetHashCode();
    }
}