Question

我有这段代码：

public string Label { get; set; }

public bool IsSpoon(out Spoon sp) 
{
    sp = null;
    foreach (Tool t in Tools.GetAllItems())
        if ((sp = t.AllSpoons.FirstOrDefault(x => x.Label == this.Label)) != null)
            break;

    return sp != null;
}

如何通过LINQ优化？

我想到了类似的东西，但这是不允许的：

public string Label { get; set; }

public bool IsSpoon(out Spoon sp) 
{
    return Tools.GetAllItems().FirstOrDefault(x => (sp = x.AllSpoons.FirstOrDefault(y => y.Label == this.Label)) != null) != null;
}

Answer 1

编辑：我没有注意到sp参数，这是更新：

sp = Tools
    .GetAllItems()
    .SelectMany(x => x.AllSpoons)
    .FirstOrDefault(y => y.Label == this.Label);
return sp != null;

Answer 2

您可以使用SelectMany展平列表。然后你不必做任何棘手的事情，比如在LINQ语句的中间分配一个值。

public bool IsSpoon(out Spoon sp) 
{
    sp = Tools.GetAllItems().SelectMany(t => t.AllSpoons)
                            .FirstOrDefault(x => x.Label == this.Label);
    return sp != null;
}

这是基本等效的查询语法：

sp = (from tool in Tools.GetAllItems()
      from spoon in tool.AllSpoons
      where spoon.Label == this.Label
      select spoon).FirstOrDefault();

Answer 3

public bool IsSpoon(out Spoon sp) 
{ 
    return Tools.GetAllItems()
        .SelectMany(t => t.AllSpoons)
        .Any(x => x.Label == this.Label);
}

LINQ选择取决于内部集合值

3 个答案: