Question

我正在使用以下代码来获取数据以绑定gridview，但是对于性能问题，我只想获得选定的数据行范围，对于第二页，首页11-20说1-10，我该怎么办？修改以下代码

 public IQueryable<Employee> SelectEmployees(string SortColumn, string SortOrder, long UserID,---int start,---int end)
    {
            IUnitOfWork objUow;
            var arg = Expression.Parameter(typeof(Employee), "Employee");
            var sortProperty = Expression.Property(arg, SortColumn);
            var lambda = Expression.Lambda(sortProperty, arg);
            var param = Expression.Parameter(typeof(IQueryable<Employee>));
            var orderByCall = Expression.Call(typeof(Queryable), SortOrder, new Type[] { typeof(Employee), sortProperty.Type }, new Expression[] { param, lambda });
            var orderLambda = Expression.Lambda<Func<IQueryable<Employee>, IQueryable<Employee>>>(orderByCall, param).Compile();
            var Ids = objUow.Repository<Users>().Entities.Where((x => x.ID == UserID)).Select(y => y.Id);
            return orderLambda(objUow.Repository<Employee>().Entities.Where(x => x.IsDeleted != true && x.Status == 1 && Ids.Contains(x.CheckID)));
   }

我尝试过skip（）。take（）但是它重新出错了。 ......

 return orderLambda((objUow.Repository<Employee>().Entities.Where(x => x.IsDeleted != true && x.Status == 1 && Ids.Contains(x.CheckID))).Skip(0).Take(10));

类型＆＃39; System.NotSupportedException＆＃39;的例外情况发生在EntityFramework.SqlServer.dll中但未在用户代码中处理

其他信息：方法＆＃39; Skip＆＃39;仅支持LINQ to Entities中的排序输入。方法＆＃39; OrderBy＆＃39;必须在方法之前调用＆＃39;跳过＆＃39;。

我可以做下面的事吗

 IQueryable<Employee> Obj= orderLambda(objUow.Repository<Employee>().Entities.Where(x => x.IsDeleted != true && x.InvalidStatus == 1 && shopids.Contains(x.CheckID)));
           Obj.Skip(0).Take(10);

Answer 1

 return orderLambda((objUow.Repository<Employee>()
  .Entities.Where(x => x.IsDeleted != true && x.Status == 1 && Ids.Contains(x.CheckID)))
  .OrderBy(x=> x.CheckID) // you must order the results before skip and take
  .Skip(0)
  .Take(10));

错误告诉你

修改

要按字符串排序，您可能需要System.Linq.Dynamic nuget包和命名空间。然后你可以用OrderBy（SortOrder）替换我的OrderBy 然后就可以了

OrderBy(string.Format("{0} {1}", SortOrder, SortDirection)) // where Sort direction can be "descending" if it's reversed // replace 0 & 10 as appropriate

Answer 2

每次查询数据库时，您都需要知道要跳过的记录数。为此，您应该将页码乘以页面大小。这是一个例子：

int skipAmount = pageNumber * pageSize;
_repository.Where(a => a.IsDeleted != false)
   .OrderBy(a => a.Date)
      .Skip(skipAmount)
         .Take(pageSize);

如何使用.skip（i）.take（j）使用lambda表达式导航从数据库中获取给定范围的数据行

2 个答案: