c# - 使用 C#，是否可以在不定义大量类型的情况下查询 YAML？

Question

我需要使用 Kubernetes 生成的 YAML，我希望能够在 C# 中使用类似 XPath 或 jq 的 DSL 表示法读取特定属性。

Kubernetes 生成的 YAML 的结构和性质在大多数地方都是明确定义的，但在某些情况下是任意的并且来自用户输入，因此不可能预先定义可以捕获整个结构的静态类型YAML。

在 C# 中反序列化和读取 YAML 的最流行的解决方案似乎是 YamlDotNet ，但它主要用于反序列化为完全类型化的对象。

我宁愿不必定义一堆静态类型或进行大量繁琐的转换只是为了获取一个或两个字段或聚合它们。我理想的方法应该是这样的:

var reader = new FileReader("my-file.yaml");
List<string> listOfPodNames = Yaml.Deserialize(reader)
                                  .Query(".pods[*].name")
                                  .AsList;
// expected result: list of all pod names as strings

这是否可以通过 YamlDotNet 或 C# 中其他类似且得到良好支持的工具实现？

更新:我尝试了多种方法，但最终，效果最好的方法是重新序列化为 JSON，然后使用支持更好的 Json.NET 进行查询。

Answer 1

在不指定目标类型的情况下使用 YamlDotNet 反序列化机制时，我们总是得到一个字典(映射)、一个键值对列表(列表)或单个键值对/字符串(标量)。KeyValuePairs 将包含另一个字典、另一个列表或实际值。

我们现在可以实现一个查询功能:

var data = new YamlQuery(yamlObject)
                        .On("pods")  // parent
                      // this functionality could be implemented as well wihtout much effort
                      //.Where("ignore").Equals(true)
                        .Get("name") // propery
                        .ToList<string>();

编辑:多个嵌套值

var data = new YamlQuery(yamlObject)
                .On("ressources")
                .On("pods")
                .Get("name")
                .ToList<string>();

工作示例:https://dotnetfiddle.net/uNQPyl

using System.IO;
using System;
using System.Linq;
using YamlDotNet.Serialization;
using System.Collections.Generic;
using YamlDotNet.RepresentationModel;

namespace ConsoleApp1
{
    public class Program
    {
        public static void Main()
        {
            object yamlObject;
            using (var r = new StringReader(Program.Document))
                yamlObject = new Deserializer().Deserialize(r);

            var data = new YamlQuery(yamlObject)
                                .On("pods")
                                .Get("name")
                                .ToList<string>();
            Console.WriteLine("all names of pods");
            Console.WriteLine(string.Join(",", data));


            data = new YamlQuery(yamlObject)
                    .On("ressources")
                    .On("pods")
                    .Get("name")
                    .ToList<string>();
            Console.WriteLine("all names of pods in ressources");
            Console.WriteLine(string.Join(",", data));

        }

        public class YamlQuery
        {
            private object yamlDic;
            private string key;
            private object current;

            public YamlQuery(object yamlDic)
            {
                this.yamlDic = yamlDic;
            }

            public YamlQuery On(string key)
            {
                this.key = key;
                this.current = query<object>(this.current ?? this.yamlDic, this.key, null);
                return this;
            }
            public YamlQuery Get(string prop)
            {
                if (this.current == null)
                    throw new InvalidOperationException();

                this.current = query<object>(this.current, null, prop, this.key);
                return this;
            }

            public List<T> ToList<T>()
            {
                if (this.current == null)
                    throw new InvalidOperationException();

                return (this.current as List<object>).Cast<T>().ToList();
            }

            private IEnumerable<T> query<T>(object _dic, string key, string prop, string fromKey = null)
            {
                var result = new List<T>();
                if (_dic == null)
                    return result;
                if (typeof(IDictionary<object, object>).IsAssignableFrom(_dic.GetType()))
                {
                    var dic = (IDictionary<object, object>)_dic;
                    var d = dic.Cast<KeyValuePair<object, object>>();

                    foreach (var dd in d)
                    {
                        if (dd.Key as string == key)
                        {
                            if (prop == null)
                            { 
                                result.Add((T)dd.Value);
                            } else
                            { 
                                result.AddRange(query<T>(dd.Value, key, prop, dd.Key as string));
                            }
                        }
                        else if (fromKey == key && dd.Key as string == prop)
                        { 
                            result.Add((T)dd.Value);
                        }
                        else
                        { 
                            result.AddRange(query<T>(dd.Value, key, prop, dd.Key as string));
                        }
                    }
                }
                else if (typeof(IEnumerable<object>).IsAssignableFrom(_dic.GetType()))
                {
                    var t = (IEnumerable<object>)_dic;
                    foreach (var tt in t)
                    {
                        result.AddRange(query<T>(tt, key, prop, key));
                    }

                }
                return result;
            }
        }




        private const string Document = @"---
            receipt:    Oz-Ware Purchase Invoice
            date:        2007-08-06
            customer:
                given:   Dorothy
                family:  Gale

            pods:
                - name:   pod1
                  descrip:   Water Bucket (Filled)
                  price:     1.47
                  quantity:  4


                - name:   pod2
                  descrip:   High Heeled ""Ruby"" Slippers
                  price:     100.27
                  quantity:  1
                - name:   pod3
                  descrip:   High Heeled ""Ruby"" Slippers
                  ignore:    true
                  quantity:  1

            bill-to:  &id001
                street: |-
                        123 Tornado Alley
                        Suite 16
                city:   East Westville
                state:  KS
                pods:
                    - name: pod4
                      descrip:   High Heeled ""Ruby"" Slippers
                      price:     100.27
                      quantity:  
            ressources:
                      - pids:
                            - id: 1
                            - name: pid
                      - pods: 
                            - name: pod5
                              descrip:   High Heeled ""Ruby"" Slippers
                              price:     100.27
                              quantity:  
                            - name: pod6
                              descrip:   High Heeled ""Ruby"" Slippers
                              price:     100.27
                              quantity:  
            specialDelivery: >
                Follow the Yellow Brick
                Road to the Emerald City.
                Pay no attention to the
                man behind the curtain.

...";
    }

}