两表关联查询，根据某一列去重复

 var product = (from p in dbContext.Product
                               join gp in dbContext.GroupProduct on p.Id equals gp.ProductId
                               where p.IsActive == true && p.ProductStatus == true

                               select new GroupProductInfo() {Id = gp.Id});

var distinctProduct = product.GroupBy(c => c.ProductId)

                                                .Select(c => c.FirstOrDefault())

                                                .OrderByDescending(c => c.IsRecommend).ToList();