yamldotnet - 如何在 Yamldotnet 中跳过空集合

Question

我正在尝试弄清楚如何使用 YamlDotNet 跳过序列化空集合。我对自定义 ChainedObjectGraphVisitor 和 IYamlTypeConverter 进行了试验。我是使用 YamlDotNet 的新手，这里有一些知识空白。

下面是我对访问者模式的实现，它导致了 YamlDotNet.Core.YamlException "Expected SCALAR, SEQUENCE-START, MAPPING-START, or ALIAS, got MappingEnd" 错误。我确实看到了一些关于 MappingStart/MappingEnd 的在线内容，但我不确定它如何适合我正在尝试做的事情(消除大量空集合中的困惑)。任何指向正确方向的指示都将受到赞赏。

实例化序列化器:

var serializer = new YamlDotNet.Serialization.SerializerBuilder()
                .WithNamingConvention(new YamlDotNet.Serialization.NamingConventions.CamelCaseNamingConvention())
                .WithEmissionPhaseObjectGraphVisitor(args => new YamlIEnumerableSkipEmptyObjectGraphVisitor(args.InnerVisitor))
                .Build();

ChainedObjectGraphVisitor 实现:

    public sealed class YamlIEnumerableSkipEmptyObjectGraphVisitor : ChainedObjectGraphVisitor
{
    public YamlIEnumerableSkipEmptyObjectGraphVisitor(IObjectGraphVisitor<IEmitter> nextVisitor)
        : base(nextVisitor)
    {
    }

    public override bool Enter(IObjectDescriptor value, IEmitter context)
    {
        bool retVal;

        if (typeof(System.Collections.IEnumerable).IsAssignableFrom(value.Value.GetType()))
        {   // We have a collection
            var enumerableObject = (System.Collections.IEnumerable)value.Value;
            if (enumerableObject.GetEnumerator().MoveNext()) // Returns true if the collection is not empty.
            {   // Serialize it as normal.
                retVal = base.Enter(value, context);
            }
            else
            {   // Skip this item.
                retVal = false;
            }
        }
        else
        {   // Not a collection, normal serialization.
            retVal = base.Enter(value, context);
        }

        return retVal;
    }
}

Answer 1

我相信答案也是用与在 Enter() 方法中所做的类似的逻辑覆盖基类中的 EnterMapping() 方法:

public override bool EnterMapping(IPropertyDescriptor key, IObjectDescriptor value, IEmitter context)
{
    bool retVal = false;

    if (value.Value == null)
        return retVal;

    if (typeof(System.Collections.IEnumerable).IsAssignableFrom(value.Value.GetType()))
    {   // We have a collection
        var enumerableObject = (System.Collections.IEnumerable)value.Value;
        if (enumerableObject.GetEnumerator().MoveNext()) // Returns true if the collection is not empty.
        {   // Don't skip this item - serialize it as normal.
            retVal = base.EnterMapping(key, value, context);
        }
        // Else we have an empty collection and the initialized return value of false is correct.
    }
    else
    {   // Not a collection, normal serialization.
        retVal = base.EnterMapping(key, value, context);
    }

    return retVal;
}