我对这个类有困扰,尤其是这个方法:
public IQueryable<T> ExecuteOrderBys<T>(this IQueryable<T> source)
它显示以下错误:
扩展方法必须是静态的
但是当我将方法改为静态时,它抛出其他区域的错误,特别是无法在静态方法中访问this.xxx
。
关于<T>
和返回类型的返回类型,我有些困惑,请有经验的人解释一下它是如何工作的,我将不胜感激。
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Collections;
/// <summary>
/// A collection of order bys
/// </summary>
public class OrderByCollection
{
private ArrayList Orderings = new ArrayList();
public int? Skip { get; set; }
public int? Take { get; set; }
public OrderByCollection()
{
// Default skip and takes to nulls so we know if they are set or not
this.Skip = null;
this.Take = null;
}
/// <summary>
/// Add an order by to this collection
/// </summary>
public void AddOrderBy(string Field, bool Descending)
{
OrderByObj NewObj = new OrderByObj(Descending, Field);
this.Orderings.Add(NewObj);
}
/// <summary>
/// Executes the order bys
/// </summary>
public IQueryable<T> ExecuteOrderBys<T>(this IQueryable<T> source)
{
int ExecutionIndex = 0;
foreach (OrderByObj O in this.Orderings)
{
if (ExecutionIndex == 0)
{
if (O.Descending)
source = LinqHelper.OrderByDescending(source, O.Field);
else
source = LinqHelper.OrderBy(source, O.Field);
}
else
{
if (O.Descending)
source = LinqHelper.ThenByDescending((IOrderedQueryable<T>)source, O.Field);
else
source = LinqHelper.ThenBy((IOrderedQueryable<T>)source, O.Field);
}
ExecutionIndex++;
}
// Skip and take
if (this.Skip != null)
source = source.Skip(this.Skip.Value);
if (this.Take != null)
source = source.Take(this.Take.Value);
return (IOrderedQueryable<T>)source;
}
}
编辑
我正在尝试创建一个能够执行以下操作的类:
var q = db.tblJobHeaders;
OrderByCollection OBys = new OrderByCollection();
OBys.AddOrderBy("some field", true);
OBys.AddOrderBy("anotherfield", false);
OBys.ExecuteOrderBys(q);