Linq 中的拼接条件

public IQueryable<BBS_Theme> GetListPage(int PageSize, int PageIndex, NameValueCollection nvcParamWhere, NameValueCollection nvcorderby, ref int AllCount)
      {
          #region where
          var searchPredicate = PredicateExtensions.True<BBS_Theme>();
          if (nvcParamWhere != null)
          {
              foreach (string key in nvcParamWhere)
              {
                  string condition = string.Empty;
                  switch (key)
                  {
                      #region
                      case "ID":
                          condition = nvcParamWhere[key];
                          searchPredicate = searchPredicate.And(u => u.ID.Equals(condition));
                          break;
                      case "LableID":
                          condition = nvcParamWhere[key];
                          searchPredicate = searchPredicate.And(u => u.LableID.Equals(condition));
                          break;
 
           
                       
                      default:
                          break;
 
                      #endregion
                  }
              }
          }
          #endregion
           
          #region queryable
          var linq = (from a in db.BBS_Theme
                      select a)
                      .Where(searchPredicate);
          #endregion 
           
          #region orderby
          if (nvcorderby != null)
          {
              foreach (string key in nvcorderby)
              {
                  string condition = string.Empty;
 
                  switch (key)
                  {
                      case "ID":
                          condition = nvcorderby[key];
                          if(bool.Parse(condition))
                          {
                              linq = linq.OrderBy(o=>o.ID);
                          }
                          else
                          {
                              linq = linq.OrderByDescending(o => o.ID);
                          }
                          break;
                      //........省略n个case
                       
                      default:
                          break;
 
                  }
              }
          }
          #endregion
           
          AllCount = linq.Count();
          linq = linq.Skip(PageSize * (PageIndex - 1)).Take(PageSize);
          return linq;
      }