我可以依次读取YamlDotNet映射吗？

Question

是否可以按照它们在源文档中出现的相同顺序访问映射的键？即如果我有这个简单的文档：

values: 
    first: something1 
    second: something2 
    third: something3 

然后我就能够拿到钥匙的序列中的原始顺序：第一，第二，第三]

Answer 1

实现此目的的一种方法是使用RepresentationModel API。它允许获得YAML文档的底层结构紧密匹配的表示：

var stream = new YamlStream(); 
stream.Load(new StringReader(yaml)); 

var document = stream.Documents.First(); 

var rootMapping = (YamlMappingNode)document.RootNode; 
var valuesMapping = (YamlMappingNode)rootMapping.Children[new YamlScalarNode("values")]; 

foreach(var tuple in valuesMapping.Children) 
{ 
    Console.WriteLine("{0} => {1}", tuple.Key, tuple.Value); 
} 

这种方法的缺点是，你需要“手动”解析文档。另一种方法是使用序列化，并使用保留排序的类型。我不知道任何现成的使用实施IDictionary<TKey, TValue>具有此特征的，但如果你不关心性能高，它是相当简单的实现：

// NB: This is a minimal implementation that is intended for demonstration purposes. 
//  Most of the methods are not implemented, and the ones that are are not efficient. 
public class OrderPreservingDictionary<TKey, TValue> 
    : List<KeyValuePair<TKey, TValue>>, IDictionary<TKey, TValue> 
{ 
    public void Add(TKey key, TValue value) 
    { 
     Add(new KeyValuePair<TKey, TValue>(key, value)); 
    } 

    public bool ContainsKey(TKey key) 
    { 
     throw new NotImplementedException(); 
    } 

    public ICollection<TKey> Keys 
    { 
     get { throw new NotImplementedException(); } 
    } 

    public bool Remove(TKey key) 
    { 
     throw new NotImplementedException(); 
    } 

    public bool TryGetValue(TKey key, out TValue value) 
    { 
     throw new NotImplementedException(); 
    } 

    public ICollection<TValue> Values 
    { 
     get { throw new NotImplementedException(); } 
    } 

    public TValue this[TKey key] 
    { 
     get 
     { 
      return this.First(e => e.Key.Equals(key)).Value; 
     } 
     set 
     { 
      Add(key, value); 
     } 
    } 
} 

一旦你有了这样的容器，你可以采取Serialization API的优势来解析文档：

var deserializer = new Deserializer(); 
var result = deserializer.Deserialize<Dictionary<string, OrderPreservingDictionary<string, string>>>(new StringReader(yaml)); 

foreach(var tuple in result["values"]) 
{ 
    Console.WriteLine("{0} => {1}", tuple.Key, tuple.Value); 
} 

You can see a fully working example in this fiddle