C Sharp - Linq - DefaultIfEmpty

.DefaultIfEmpty

Sample

var query =
    (	from c in _context.Categories
      	join p in _context.Programs on c.Id equals p.CategoryId into Programs
       	from program in Programs.DefaultIfEmpty() where program.IsDeleted == false
       	join r in _context.Permits on c.Id equals r.CategoryId into Permits
       	from permit in Permits.DefaultIfEmpty() where permit.IsDeleted == false
        where c.Id == id 
        select new { program, permit }
    ).Distinct();

DefaultIfEmpty is only useful if you provide a default object. in this case that is used here, if there are no programs, then ‘program’ will be null, and program.IsDeleted will throw exception.