各种派生类型集合上的通用LINQ到SQL扩展方法
本文关键字:LINQ SQL 方法 扩展 派生 类型 集合 | 更新日期: 2023-09-27 18:29:18
我正在尝试为IQueryable<T>
创建一个通用扩展方法。T是抽象的Player
,并且IQueryable可以包含具体类型Goalkeeper
和Striker
。
public abstract class Player
{
public string Name { get; set; }
public string Fouls { get; set; }
}
public class Goalkeeper : Player
{
public int Saves { get; set; }
}
public class Striker : Player
{
public int Goals { get; set; }
}
正在工作的扩展方法(简单的)如下所示:
public static IQueryable<Goalkeeper> NotPerforming(this IQueryable<Goalkeeper> goalkeepers)
{
return goalkeepers.Where(g => g.Saves < goalkeepers.Average(x => x.Saves));
}
public static IQueryable<Striker> NotPerforming(this IQueryable<Striker> strikers)
{
return strikers.Where(g => g.Goals < strikers.Average(x => x.Goals));
}
我可以这样使用:
var badGoalies = players.OfType<Goalkeeper>().NotPerforming();
var badStrikers = players.OfType<Striker>().NotPerforming();
所以现在我想查询所有表现不佳的玩家。
var badPlayers = players.NotPerforming();
我似乎无法正常工作。
public static IQueryable<T> NotPerforming<T>(this IQueryable<T> players)
where T : Player
{
// what to do here?
}
我试过。。。
return players.OfType<Striker>().NotPerforming()
.Union(
players.OfType<Goalkeeper>().NotPerforming()
);
这不起作用。
做到这一点的最佳实践方式是什么?在不因为我想继续链接扩展方法而将LINQ留给SQL的情况下,并记住良好的性能?
您可以创建另一个扩展方法,并在其中放入一个逻辑:
public static IQueryable<Player> NotPerforming(this IQueryable<Player> players)
{
var notPerformingGoalKeepers = players.NotPerformingGoalkeepers();
var notPerformingStrikers = players.NotPerformingStrikers();
return notPerformingGoalKeepers.Cast<Player>()
.Concat(notPerformingStrikers);
}
public static IQueryable<Goalkeeper> NotPerformingGoalkeepers(this IQueryable<Player> players)
{
var goalkeepers = players.OfType<Goalkeeper>();
return goalkeepers.Where(g => g.Saves < goalkeepers.Average(x => x.Saves));
}
public static IQueryable<Striker> NotPerformingStrikers(this IQueryable<Player> players)
{
var strikers = players.OfType<Striker>();
return strikers.Where(g => g.Goals < strikers.Average(x => x.Goals));
}
使用:
var badPlayers = players.NotPerforming();
或者另一种方法:
public static IQueryable<Player> NotPerforming<T>(this IQueryable<Player> players) where T : Player
{
if (typeof(T) == typeof(Goalkeeper))
{
return players.OfType<Goalkeeper>().NotPerforming();
}
if (typeof(T) == typeof(Striker))
{
return players.OfType<Striker>().NotPerforming();
}
return null;
}
private static IQueryable<Goalkeeper> NotPerforming(this IQueryable<Goalkeeper> goalkeepers)
{
return goalkeepers.Where(g => g.Saves < goalkeepers.Average(x => x.Saves));
}
private static IQueryable<Striker> NotPerforming(this IQueryable<Striker> strikers)
{
return strikers.Where(g => g.Goals < strikers.Average(x => x.Goals));
}
使用:
var badStrikers = players.NotPerforming<Striker>();
var badGoalkeepers = players.NotPerforming<Goalkeeper>();
var badPlayers = players.NotPerforming<Striker>()
.Concat(players.NotPerforming<Goalkeeper>());