动态 linq 嵌套组

Question

如何做动态嵌套组？

假设我有这个例子：

result.GroupBy(f => f.level1)
              .Select(l1 => new {
                  name = l1.Key,
                  children = l1.GroupBy(l2 => l2.level2)
                    .Select(l2 => new {
                        name = l2.Key,
                        children = l2.GroupBy(l3 => l3.level3)
                            .Select(l3 => new {
                                name = l3.Key,
                                children = new someObject()
                  });

我如何将其更改为按参数动态分组。从更深层次开始，继续前进。

Answer 1

如果你想真正动态嵌套它，我不会将关卡名称作为属性存储在你的关卡对象中，而是将它们放在一个数组中，以便你可以以某种方式循环它们。

话虽如此，你可以构建一个通用的 NestedGroupBy<> Linq 扩展方法来处理你想要做的事情，你只需要为你想要的每个级别传递一个 lambda：

// The NestedGroupBy<> extension method
public static class LinqExtensions
{
    public static IEnumerable<TTarget> NestedGroupBy<TSource, TTarget, TKey>(this IEnumerable<TSource> source, Func<TKey, IEnumerable<TTarget>, TTarget> factory, params Func<TSource, TKey>[] keySelectors)
    {
        return source.NestedGroupBy(factory, keySelectors, 0);
    }
    private static IEnumerable<TTarget> NestedGroupBy<TSource, TTarget, TKey>(this IEnumerable<TSource> source, Func<TKey, IEnumerable<TTarget>, TTarget> factory, Func<TSource, TKey>[] keySelectors, int selectorIndex)
    {
        // reached the end, just return an empty list
        if(selectorIndex >= keySelectors.Length)
        {
            return new List<TTarget>();
        }
        // do the GroupBy using the function at index selectorIndex in our list to find the key (level name)
        // then call the factory to construct the target SomeObject, passing it the key and the recursive call to NestedGroupBy<>
        return source.GroupBy(keySelectors[selectorIndex])
            .Select(f => factory(
                f.Key,
                f.NestedGroupBy(factory, keySelectors, selectorIndex + 1)
            )
        );
    }
}
// source object - assuming your result variable is List<LevelObject>
public class LevelObject
{
    public string level1 {get;set;}
    public string level2 {get;set;}
    public string level3 {get;set;}
    public LevelObject(string level1, string level2, string level3)
    {
        this.level1 = level1;
        this.level2 = level2;
        this.level3 = level3;
    }
}
// target object - what we will end up with in our final list
// the constructor is optional - it just makes the NestedGroupBy<> call cleaner.
public class SomeObject
{
    public string name {get; set;}
    public IEnumerable<SomeObject> children {get; set;}
    public SomeObject(string name, IEnumerable<SomeObject> children)
    {
        this.name = name;
        this.children = children;
    }
}
// Sample code to use it. The JToken/JsonConvert call at the end just pretty prints the result on screen.
public static void Main()
{
    List<LevelObject> result = new List<LevelObject>()
    {
        new LevelObject("L1a1", "L2a1", "L3a1"),
        new LevelObject("L1a1", "L2a2", "L3a1"),
        new LevelObject("L1a1", "L2a1", "L3a2"),
        new LevelObject("L1b1", "L2b1", "L3b1"),
        new LevelObject("L1c1", "L2c1", "L3c1")
    };
    /* old way - produces same result
            var groupings = result.GroupBy(f => f.level1)
                  .Select(l1 => new SomeObject {
                      name = l1.Key,
                      children = l1.GroupBy(l2 => l2.level2)
                        .Select(l2 => new SomeObject{
                            name = l2.Key,
                            children = l2.GroupBy(l3 => l3.level3)
                                .Select(l3 => new SomeObject{
                                    name = l3.Key,
                                    children = new List<SomeObject>()
                                })})}).ToList();
    */
    var groupings = result.NestedGroupBy<LevelObject, SomeObject, string>(
        (key, children) => new SomeObject(key, children),
        l => l.level1, l => l.level2, l => l.level3
    ).ToList();
    Console.WriteLine(groupings.GetType());
    Console.WriteLine(JToken.Parse(JsonConvert.SerializeObject(groupings)));
}