linq两个list合并查询

 IList<ts_dynamic> dynamicList = null;

            var allDynamic = (new ts_dynamicService()).GetAllDynamicByCompanyId(companyId);

            if (!string.IsNullOrEmpty(userId) && string.IsNullOrEmpty(groupId))

                dynamicList = allDynamic.Where(x => x.shareType == 4 && x.shareObjectId == userId)

                    .Select(y => new ts_dynamic { hirerId = y.hirerId, contentId = y.contentId }).ToList();//@我的动态

            else if (string.IsNullOrEmpty(userId) && string.IsNullOrEmpty(groupId))

                dynamicList = allDynamic.Select(y => new ts_dynamic { hirerId = y.hirerId, contentId = y.contentId }).ToList();

            else

                dynamicList = allDynamic.Where(x => x.shareType == 1 && x.shareObjectId == groupId)

                      .Select(y => new ts_dynamic { hirerId = y.hirerId, contentId = y.contentId }).ToList();//所在群组动态

            //根据查询到的动态再去查附件

//上面代码已经取到动态表中的hirerId和contentId 

//下面要根据上面的hirerId和contentId 去GetAllAttachByCompanyId取到的附件表中查询匹配的所有附件

            var attachs = GetAllAttachByCompanyId(companyId).Where(x => x.hirerId==dynamicList//此处并没有dynamicList.hireId,但是数据库中是有的);

请问linq怎么写啊？
------解决方案--------------------

List<CourseBookingEDM> listbooking1 = BOSUtility.ConvertToCourseBookingEDM(indvlist);

List<CourseBookingEDM> listbooking2 = BOSUtility.ConvertToCourseBookingEDM(complist);

listbooking1.AddRange(listbooking2);

------解决方案--------------------
 var attachs = from GetAllAttachByCompanyId(companyId) in dynamicList 
                    where x => x.hirerId==dynamicList
                    select new
                    {
                        附件 = GetAllAttachByCompanyId(companyId).附件
                                           };
foreach (var item in attachs)
        {
            Response.Write(item + "<br/>");
        }