如何保存属性引用

Question

我正在设置一个automapper配置文件来将Revit元素（从它们的api）映射到一些自定义元素。他们的API得到了循环引用（1个元素=> n个参数，1个参数=> 1个元素）我调用了PreserveReference（）方法。但它似乎没有用，因为我有一个StackOverflowException。那么，我想知道PreserveReference是如何工作的？我可以指定一个属性来检查相等性而不是使用引用吗？

public class Element
{
    public int Id { get; set; }

    public List<Parameter> Parameters { get; set; }

    public override bool Equals(object obj)
    {
        return obj is Element element && Id == element.Id;
    }

    public override int GetHashCode()
    {
        // ReSharper disable once NonReadonlyMemberInGetHashCode
        return Id;
    }
}

public class Parameter
{
    public int Id { get; set; }

    public Definition Definition { get; set; }

    public Element Element { get; set; }
}


profile.CreateMap<Element, Models.Element>()
            .ForMember(element => element.Id, expression => expression.MapFrom(element => element.Id.IntegerValue))
            .IncludeAllDerived()
            .PreserveReferences();

profile.CreateMap<Parameter, Models.Parameter>()
            .ForMember(parameter => parameter.Id, expression => expression.MapFrom(parameter => parameter.Id.IntegerValue))
            .IncludeAllDerived()
            .PreserveReferences();

Answer 1

我找到了一种方法来获得我想要的东西。我不得不访问这样的私有财产：

public static T GetSource<T>(this ContextCacheKey contextCacheKey)
    {
        var source = (T)typeof(ContextCacheKey).GetField("_source", BindingFlags.NonPublic | BindingFlags.GetField | BindingFlags.Instance)?.GetValue(contextCacheKey);

        return source;
    }

    public class ElementConverter : IValueConverter<Element, Models.Element>
    {
        public Models.Element Convert(Element sourceMember, ResolutionContext context)
        {
            var a = (Models.Element)context.InstanceCache.FirstOrDefault(kvp => kvp.Key.GetSource<Element>().Id.Equals(sourceMember.Id)).Value ?? context.Mapper.Map<Models.Element>(sourceMember);

            return a;
        }
    }

一个简单的解决方案是在ContextCacheKey struc中公开Source和DestinationType：

public struct ContextCacheKey : IEquatable<ContextCacheKey>
{
    public static bool operator ==(ContextCacheKey left, ContextCacheKey right) => left.Equals(right);
    public static bool operator !=(ContextCacheKey left, ContextCacheKey right) => !left.Equals(right);

    public readonly object _source;
    public readonly Type _destinationType;

    public ContextCacheKey(object source, Type destinationType)
    {
        _source = source;
        _destinationType = destinationType;
    }

    public override int GetHashCode() => HashCodeCombiner.Combine(_source, _destinationType);

    public bool Equals(ContextCacheKey other) =>
        _source == other._source && _destinationType == other._destinationType;

    public override bool Equals(object other) => 
        other is ContextCacheKey && Equals((ContextCacheKey)other);
}