Class Record
{
   int Id
   int StartDate
}

Class DBRecord
{
   int Id
   DateTime StartDate
   DateTime EndDate
}

this.Records().Join(context.DBRecords,
          x=> new { x.Id, x.StartDate},
         (x, y) => { x.Id == y.Id, x.StartDate > y.StartDate && x.startDate < x.endDate  },
         (x,y) => y);