Answer by Sergey Berezovskiy for how to convert list to IEnumerable?

Problem is not in convertation of List<T> to IEnumerable<T>. Becuase List<T> implements IEnumerable<T>.

Your problem is that generic parameters are different. You are trying to convert List<T1> to IEnumerable<T2>. Where:

• T1 is QlasrService.EntityFramework.tblSoftwareImageTestPlan
• T2 is QlasrService.Model.SchemaModels.LAP.SoftwareImageTestPlan

Simplest solution will be mapping (either manual or automatic). Automatic mapping is very easy. Add Automapper nuget package. Place this line somewhere on application start:

Mapper.Initialize(cfg => cfg.CreateMap<tblSoftwareImageTestPlan, SoftwareImageTestPlan>());

And now your method will look like:

public IEnumerable<SoftwareImageTestPlan> GetAssignedTestPlansForSPSI(
   int SoftwareProductID, int SoftwareImageID)
{
    var testPlans = from tp in _entities.tblSoftwareImageTestPlans
                    where tp.SoftwareProductID == SoftwareProductID && tp.SoftwareImageID == SoftwareImageID
                    select tp;

    return Mapper.Map<IEnumerable<SoftwareImageTestPlan>>(testPlans);
}

NOTE: In your code either records cannot have null value, or you will have NullReferenceException at ToList() call. So if..else block is useless anyway.