覆盖抽象类的属性
ODS List是抽象类的集合，它为分页/排序的对象数据源实现过滤的select方法。我定义了三个absract类，它们代表过滤器，返回的数据和产生这些结果的方法：
[Serializable]
public abstract class ListFilter
{
// Define filter properties
}
[Serializable]
public abstract class ListData
{
// Define properties to be returned from the query
}
public abstract class ListMethods
{
public int ListCount(ListFilter filter)
{
var rows = listQuery();
rows = listFilter(rows, filter);
return rows.Count();
}
/// <summary>
/// List returns a page of data
/// </summary>
/// <param name="filter"></param>
/// <param name="sortType"></param>
/// <param name="startRowIndex"></param>
/// <param name="maximumRows"></param>
/// <returns></returns>
public IEnumerable<ListData> List(ListFilter filter, string sortType, int startRowIndex, int maximumRows)
{
var rows = listQuery();
rows = listFilter(rows, filter);
rows = listSort(rows, sortType);
return rows.Distinct().Skip(startRowIndex).Take(maximumRows).ToList();
}
public abstract IQueryable<ListData> listQuery();
public virtual IQueryable<ListData> listFilter(IQueryable<ListData> rows, ListFilter filter)
{
return rows;
}
public virtual IQueryable<ListData> listSort(IQueryable<ListData> rows, string sortType)
{
bool sortDescending = false;
if (!string.IsNullOrEmpty(sortType))
{
string[] values = sortType.Split(' ');
sortType = values[0];
if (values.Length > 1)
{
sortDescending = values[1] == "DESC";
}
}
if (!string.IsNullOrEmpty(sortType))
{
if (sortDescending)
{
rows = rows.OrderBy(sortType + " DESC");
}
else
{
rows = rows.OrderBy(sortType);
}
}
return rows;
}
}
[Serializable]
public class EmployeeData : ODSList.ListData
{
public int EmployeeId { get; set; }
public int? ReportsToId { get; set; }...
}
public override IQueryable<ListData> listQuery()
{
var dc = new NorthwindDataContext();
var allrows = from emp in dc.Employees
select new EmployeeData()
{
EmployeeId = emp.EmployeeID,
ReportsToId = emp.ReportsTo, ...
};
return (IQueryable<ListData>)allrows; <-- PROBLEM ENCOUNTERED HERE
}
1[BusinessLayer.EmployeeData]' to type 'System.Linq.IQueryable
没有找到相关结果
已邀请:
2 个回复
阀傻
public override IQueryable<ListData> listQuery() { var dc = new NorthwindDataContext(); var allrows = from emp in dc.Employees select new EmployeeData() { EmployeeId = emp.EmployeeID, ReportsToId = emp.ReportsTo, ... } as ListData; return allrows.OfType<ListData>(); }藕挝
我不确定，但你可能需要这样做return allrows.Cast<ListData>().AsQueryable(); // if EmployeeData inherits from ListData; it is not required. // but i'm not sure if ListData is the same as ODSList.ListData