Handling decimal values in Newtonsoft.Json

Question

Edit: It\'s been almost 5 years and I don\'t think this is the way to go. The client should post the data in the correct numerical format. With current fram

Answer 1

As an extension to Kwaazaar's answer, I have added the reverse way to the converter as well (In his example it throws a NotImplementedException.

namespace Something.Converter
{
    using System;

    using Newtonsoft.Json;
    using Newtonsoft.Json.Linq;

    /// <inheritdoc cref="JsonConverter"/>
    /// <summary>
    /// Converts an object to and from JSON.
    /// </summary>
    /// <seealso cref="JsonConverter"/>
    public class DecimalConverter : JsonConverter
    {
        /// <summary>
        /// Gets a new instance of the <see cref="DecimalConverter"/>.
        /// </summary>
        public static readonly DecimalConverter Instance = new DecimalConverter();

        /// <inheritdoc cref="JsonConverter"/>
        /// <summary>
        /// Determines whether this instance can convert the specified object type.
        /// </summary>
        /// <param name="objectType">Type of the object.</param>
        /// <returns>
        ///     <c>true</c> if this instance can convert the specified object type; otherwise, <c>false</c>.
        /// </returns>
        /// <seealso cref="JsonConverter"/>
        public override bool CanConvert(Type objectType)
        {
            return objectType == typeof(decimal) || objectType == typeof(decimal?);
        }

        /// <inheritdoc cref="JsonConverter"/>
        /// <summary>
        /// Reads the JSON representation of the object.
        /// </summary>
        /// <param name="reader">The <see cref="JsonReader"/> to read from.</param>
        /// <param name="objectType">Type of the object.</param>
        /// <param name="existingValue">The existing value of object being read.</param>
        /// <param name="serializer">The calling serializer.</param>
        /// <returns>The object value.</returns>
        /// <seealso cref="JsonConverter"/>
        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        {
            if (!(reader.Value is string value))
            {
                if (objectType == typeof(decimal?))
                {
                    return null;
                }

                return default(decimal);
            }

            // ReSharper disable once StyleCop.SA1126
            if (decimal.TryParse(value, out var result))
            {
                // ReSharper disable once StyleCop.SA1126
                return result;
            }

            if (objectType == typeof(decimal?))
            {
                return null;
            }

            return default(decimal);
        }

        /// <inheritdoc cref="JsonConverter"/>
        /// <summary>
        /// Writes the JSON representation of the object.
        /// </summary>
        /// <param name="writer">The <see cref="JsonWriter"/> to write to.</param>
        /// <param name="value">The value.</param>
        /// <param name="serializer">The calling serializer.</param>
        /// <seealso cref="JsonConverter"/>
        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
        {
            var d = default(decimal?);

            if (value != null)
            {
                d = value as decimal?;
                if (d.HasValue)
                {
                    d = new decimal(decimal.ToDouble(d.Value));
                }
            }

            JToken.FromObject(d ?? 0).WriteTo(writer);
        }
    }
}

To plug this into your binder, just add an instance of the converter to the Converters list in the JsonSerializerSettings object:

JsonSerializerSettings settings = new JsonSerializerSettings
{
    // Some other settings.
    Converters = new List<JsonConverter> { new DecimalConverter() }
};

or

JsonSerializerSettings settings = new JsonSerializerSettings
{
    // Some other settings.
    Converters = new List<JsonConverter> { DecimalConverter.Instance }
};

Answer 2

You can handle both formats (the JSON number representation and the masked string format) using a custom JsonConverter class like this.

class DecimalConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return (objectType == typeof(decimal) || objectType == typeof(decimal?));
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        JToken token = JToken.Load(reader);
        if (token.Type == JTokenType.Float || token.Type == JTokenType.Integer)
        {
            return token.ToObject<decimal>();
        }
        if (token.Type == JTokenType.String)
        {
            // customize this to suit your needs
            return Decimal.Parse(token.ToString(), 
                   System.Globalization.CultureInfo.GetCultureInfo("es-ES"));
        }
        if (token.Type == JTokenType.Null && objectType == typeof(decimal?))
        {
            return null;
        }
        throw new JsonSerializationException("Unexpected token type: " + 
                                              token.Type.ToString());
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

To plug this into your binder, just add an instance of the converter to the Converters list in the JsonSerializerSettings object:

JsonSerializerSettings settings = new JsonSerializerSettings
{
    NullValueHandling = NullValueHandling.Ignore,
    MissingMemberHandling = MissingMemberHandling.Ignore,
    Formatting = Formatting.None,
    DateFormatHandling = DateFormatHandling.IsoDateFormat,
    Converters = new List<JsonConverter> { new DecimalConverter() }
};

Answer 3

Thanx a lot! I was looking for a solution to make decimals always serialize in a similar manner and this post sent me in the right direction. This is my code:

    internal class DecimalConverter : JsonConverter
    {
        public override bool CanConvert(Type objectType)
        {
            return (objectType == typeof(decimal) || objectType == typeof(decimal?));
        }

        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        {
            throw new NotImplementedException();
        }

        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
        {
            Decimal? d = default(Decimal?);
            if (value != null)
            {
                d = value as Decimal?;
                if (d.HasValue) // If value was a decimal?, then this is possible
                {
                    d = new Decimal?(new Decimal(Decimal.ToDouble(d.Value))); // The ToDouble-conversion removes all unnessecary precision
                }
            }
            JToken.FromObject(d).WriteTo(writer);
        }
    }