6

我有一个问题要问你那里的 linq 专家！在 Component 实例的嵌套列表中，我需要知道其中是否存在特定类型的组件。可以用linq表达吗？考虑到可能有 application.Components[0].Components[0].Components[0]... 我的问题是针对 linq 中的递归查询！

我把实体留给你，让你对模型有一些了解。

public class Application
{
    public List<Component> Components { get; set; }
}

public class Component
{
    public ComponentType Type { get; set; }
    public List<Component> Components { get; set; }
}

public enum ComponentType
{
    WindowsService,
    WebApplication,
    WebService,
    ComponentGroup
}
4

2 回答 2

5

您想知道组件中的任何组件是否属于给定类型？

var webType = ComponentType.WebApplication;
IEnumerable<Component> webApps = from c in components
                                 from innerComp in c.Components
                                 where innerComp.Type == webType;
bool anyWebApp = webApps.Any();

innercomp.components 呢？

编辑：所以你想递归地查找给定类型的组件，而不仅仅是在顶层或第二层。然后您可以使用以下Traverse扩展方法：

public static IEnumerable<T> Traverse<T>(this IEnumerable<T> source, Func<T, IEnumerable<T>> fnRecurse)
{
    foreach (T item in source)
    {
        yield return item;

        IEnumerable<T> seqRecurse = fnRecurse(item);
        if (seqRecurse != null)
        {
            foreach (T itemRecurse in Traverse(seqRecurse, fnRecurse))
            {
                yield return itemRecurse;
            }
        }
    }
}

以这种方式使用：

var webType = ComponentType.WebApplication;
IEnumerable<Component> webApps = components.Traverse(c => c.Components)
                                 .Where(c => c.Type == webType);
bool anyWebApp = webApps.Any();

样本数据：

var components = new List<Component>() { 
    new Component(){ Type=ComponentType.WebService,Components=null },
    new Component(){ Type=ComponentType.WebService,Components=new List<Component>(){
        new Component(){ Type=ComponentType.WebService,Components=null },
        new Component(){ Type=ComponentType.ComponentGroup,Components=null },
        new Component(){ Type=ComponentType.WindowsService,Components=null },
    } },
    new Component(){ Type=ComponentType.WebService,Components=null },
    new Component(){ Type=ComponentType.WebService,Components=new List<Component>(){
        new Component(){ Type=ComponentType.WebService,Components=new List<Component>(){
            new Component(){Type=ComponentType.WebApplication,Components=null}
        } },
        new Component(){ Type=ComponentType.WindowsService,Components=null },
        new Component(){ Type=ComponentType.WebService,Components=null },
    } },
    new Component(){ Type=ComponentType.WebService,Components=null },
    new Component(){ Type=ComponentType.ComponentGroup,Components=null },
    new Component(){ Type=ComponentType.WebService,Components=null },
};
于 2012-09-07T13:00:36.843 回答
1 
if( Components.Any( c => c.Type == ComponentType.WindowsService ) )
{
   // do something
}

或者你可以做

var listContainsAtLeastOneService = 
    ( from c in Components
      where c.Type == ComponentType.WindowsService
      select c ).Any( );
于 2012-09-07T12:48:19.073 回答