我可以按顺序读取 YamlDotNet 映射吗？

Question

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

values:
    first: something1
    second: something2
    third: something3

然后我就可以按原始顺序获得一系列键：[第一，第二，第三]？

Answer 1

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

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);
}

这种方法的缺点是您需要“手动”解析文档。另一种方法是使用序列化，并使用保留顺序的类型。我不知道有任何现成的IDictionary<TKey, TValue> 实现具有此特性，但如果您不关心高性能，实现起来相当简单：

// 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，你就可以利用Serialization API 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