JSON.NET Serialization - How does DefaultReferenceResolver compare equality?

Question

I am using JSON.NET 6.0.3. I have changed PreserveReferences option as follows:

HttpConfiguration.Formatters.JsonFormatter.SerializerSettings.Pre         


        

Answer 1

JSON.NET's logic for resolving references by default just compares references using this comparer.

If you want to compare objects in a different manner, you'll have to implement a custom IReferenceResolver.

Here's an example that takes an IEqualityComparer<T> to accommodate your use case:

public class ReferenceResolver<T> : IReferenceResolver
{
    private Dictionary<string, T> stringToReference;
    private Dictionary<T, string> referenceToString;

    private int referenceCount;

    public ReferenceResolver(IEqualityComparer<T> comparer)
    {
        this.stringToReference = new Dictionary<string, T>();
        this.referenceToString = new Dictionary<T, string>(comparer);
        this.referenceCount = 0;
    }

    public void AddReference(
        object context,
        string reference,
        object value)
    {
        this.referenceToString.Add((T)value, reference);
        this.stringToReference.Add(reference, (T)value);
    }

    public string GetReference(
        object context,
        object value)
    {
        string result = null;

        if (!this.referenceToString.TryGetValue((T)value, out result))
        {
            referenceCount++;
            result = referenceCount.ToString(CultureInfo.InvariantCulture);

            this.referenceToString.Add((T)value, result);
            this.stringToReference.Add(result, (T)value);
        }

        return result;
    }

    public bool IsReferenced(
        object context,
        object value)
    {
        return this.referenceToString.ContainsKey((T)value);
    }

    public object ResolveReference(
        object context,
        string reference)
    {
        T r = default(T);

        this.stringToReference.TryGetValue(reference, out r);
        return r;
    }
}

Answer 2

Json.Net will call the Equals method on the objects being compared. In certain scenarios you may not want this however for example when it is checking for circular references it does the same whereas it may be more ideal to check for reference equality. They do this however to give the developer full control by overridding the Equals method in their classes.

You can override the default implementation. For example to make this a reference equality you would do the following:

var settings = new JsonSerializerSettings
                           {
                               EqualityComparer = new DefaultEqualityComparer(),
                           };

public class DefaultEqualityComparer : IEqualityComparer
    {
        public bool Equals(object x, object y)
        {
            return ReferenceEquals(x, y);
        }

        public int GetHashCode(object obj)
        {
            return obj.GetHashCode();
        }
    }