对于linq to sql 和linq to entity来说，当你把获取数据的方法封装了之后，总觉得还缺点什么，想了之后，应该是排序，但看了微软的orchard项目之后，觉得它的排序封装的并不好，而且还有多列排序的问题，所以，我自己又改进了一下，首先提出一个与分层无关的IOrderable接口的概念，它是为了让WEB，BLL，DATA层之间解耦的，其次增加了ThenAsc和ThenDesc让它们支持多列排序，orchard项目里，之前是使用参数来实现的，最多支持3列排序，而且不支持升降混排的情况，呵呵。
看一个IOrderable接口
/// <summary>
/// 排序规范
/// </summary>
/// <typeparam name="T"></typeparam>
public interface IOrderable<T>
{
/// <summary>
/// 递增
/// </summary>
/// <typeparam name="TKey"></typeparam>
/// <param name="keySelector"></param>
/// <returns></returns>
IOrderable<T> Asc<TKey>(global::System.Linq.Expressions.Expression<Func<T, TKey>> keySelector);
/// <summary>
/// 然后递增
/// </summary>
/// <typeparam name="TKey1"></typeparam>
/// <typeparam name="TKey2"></typeparam>
/// <param name="keySelector1"></param>
/// <returns></returns>
IOrderable<T> ThenAsc<TKey>(Expression<Func<T, TKey>> keySelector);
/// <summary>
/// 递减
/// </summary>
/// <typeparam name="TKey"></typeparam>
/// <param name="keySelector"></param>
/// <returns></returns>
IOrderable<T> Desc<TKey>(global::System.Linq.Expressions.Expression<Func<T, TKey>> keySelector);
/// <summary>
/// 然后递减
/// </summary>
/// <typeparam name="TKey"></typeparam>
/// <param name="keySelector"></param>
/// <returns></returns>
IOrderable<T> ThenDesc<TKey>(Expression<Func<T, TKey>> keySelector);
/// <summary>
/// 排序后的结果集
/// </summary>
global::System.Linq.IQueryable<T> Queryable { get; }
}
OK，下面是为接口的一个实现，这个实现我是放在Data层的，因为它是与ORM架构有关的，可能你的linq与ado.net的排序实现是不同的，所以，不能放在entity层，我的习惯是，所有linq特有的都放在linq架构的Data层（如，IQueryable，这就是linq特有的，而list,IEnumerable等扩展应该放在entity层）
namespace EntityFrameworks.Data.Core
{
/// <summary>
/// Linq架构里对集合排序实现
/// </summary>
/// <typeparam name="T"></typeparam>
public class Orderable<T> : IOrderable<T>
{
private IQueryable<T> _queryable; /// <summary>
/// 排序后的结果集
/// </summary>
/// <param name="enumerable"></param>
public Orderable(IQueryable<T> enumerable)
{
_queryable = enumerable;
} /// <summary>
/// 排序之后的结果集
/// </summary>
public IQueryable<T> Queryable
{
get { return _queryable; }
}
/// <summary>
/// 递增
/// </summary>
/// <typeparam name="TKey"></typeparam>
/// <param name="keySelector"></param>
/// <returns></returns>
public IOrderable<T> Asc<TKey>(Expression<Func<T, TKey>> keySelector)
{
_queryable = (_queryable as IOrderedQueryable<T>)
.OrderBy(keySelector);
return this;
}
/// <summary>
/// 然后递增
/// </summary>
/// <typeparam name="TKey"></typeparam>
/// <param name="keySelector"></param>
/// <returns></returns>
public IOrderable<T> ThenAsc<TKey>(Expression<Func<T, TKey>> keySelector)
{
_queryable = (_queryable as IOrderedQueryable<T>)
.ThenBy(keySelector);
return this;
}
/// <summary>
/// 递减
/// </summary>
/// <typeparam name="TKey"></typeparam>
/// <param name="keySelector"></param>
/// <returns></returns>
public IOrderable<T> Desc<TKey>(Expression<Func<T, TKey>> keySelector)
{
_queryable = _queryable
.OrderByDescending(keySelector);
return this;
}
/// <summary>
/// 然后递减
/// </summary>
/// <typeparam name="TKey"></typeparam>
/// <param name="keySelector"></param>
/// <returns></returns>
public IOrderable<T> ThenDesc<TKey>(Expression<Func<T, TKey>> keySelector)
{
_queryable = (_queryable as IOrderedQueryable<T>)
.ThenByDescending(keySelector);
return this;
}
}
}
而这个排序的方法，可以单独被BLL层使用，自己去组装它，也可以在Data层提供的GetModel()方法里直接使用，因为我的架构里已经有排序功能拟合到GetModel方法里了，看代码：
public IQueryable<TEntity> GetModel(Action<IOrderable<TEntity>> orderBy)
{
var linq = new Orderable<TEntity>(GetModel());
orderBy(linq);
return linq.Queryable;
}
如果在其它层调用，可以自己去实例化Action<IOrderable<TEntity>>这个对象，如代码：
backgroundEntities1 db = new backgroundEntities1();
DbContextRepository<WebManageUsers> user = new DbContextRepository<WebManageUsers>(db);
Action<IOrderable<WebManageUsers>> orderBy = query => query.Asc(j => j.DepartmentID)
.ThenDesc(j => j.ManageUserID);
user.GetModel(orderBy).ToList().ForEach(k =>
{
Console.WriteLine("部门：" + k.DepartmentID + ",用户 ：" + k.ManageUserID);
});
上面的代码是先对DepartmentID进行升序，再对ManageUserID进行降序，看一下结果如图：
