Unfortunately the method JsonReader.SetToken(JsonToken, Object, Boolean)
is no longer virtual. In more recent versions of Json.NET (10.0.1 or later), one must override JsonReader.Read()
and do the necessary conversion there, then update the reader’s value with the desired value type.
For instance, if you would prefer your JsonTextReader
to return Int32
instead of Int64
whenever possible, the following reader and extension method will do the job:
public class PreferInt32JsonTextReader : JsonTextReader
{
public PreferInt32JsonTextReader(TextReader reader) : base(reader) { }
public override bool Read()
{
var ret = base.Read();
// Read() is called for both an untyped read, and when reading a value typed as Int64
// Thus if the value is larger than the maximum value of Int32 we can't just throw an
// exception, we have to do nothing.
//
// Regardless of whether an Int32 or Int64 is returned, the serializer will always call
// Convert.ChangeType() to convert to the final, desired primitive type (say, Uint16 or whatever).
if (TokenType == JsonToken.Integer
&& ValueType == typeof(long)
&& Value is long)
{
var value = (long)Value;
if (value <= int.MaxValue && value >= int.MinValue)
{
var newValue = checked((int)value); // checked just in case
SetToken(TokenType, newValue, false);
}
}
return ret;
}
}
public static class JsonExtensions
{
public static T PreferInt32DeserializeObject<T>(string jsonString, JsonSerializerSettings settings = null)
{
using (var sw = new StringReader(jsonString))
using (var jsonReader = new PreferInt32JsonTextReader(sw))
{
return JsonSerializer.CreateDefault(settings).Deserialize<T>(jsonReader);
}
}
}
Then use it as follows:
object[] variousTypes = new object[] { 3.14m, 10, "test" };
string jsonString = JsonConvert.SerializeObject(variousTypes);
var settings = new JsonSerializerSettings
{
FloatParseHandling = FloatParseHandling.Decimal,
};
object[] asObjectArray = JsonExtensions.Int32PreferredDeserializeObject<object[]>(jsonString, settings);
// No assert
Assert.IsTrue(variousTypes.Select(o => o == null ? null : o.GetType()).SequenceEqual(asObjectArray.Select(o => o == null ? null : o.GetType())));
Notes:
-
Both
JsonSerializer
andJsonReader
have a settingFloatParseHandling
that controls whether floating point numbers from JSON are to be initially parsed asdouble
ordecimal
. Thus there is no reason to implement this conversion manually inRead()
. -
By using
PreferInt32JsonTextReader
you can control how the serializer deserializes values of typeobject
. Previously integer JSON values would be unconditionally deserialized tolong
(orBigInteger
if required). Nowint
will be returned if possible. This will also modify how column types are inferred byDataTableConverter
. -
Nevertheless, using
PreferInt32JsonTextReader
will not affect what happens when loading JSON into aJToken
hierarchy with, say,JToken.Load()
, because the method that builds the hierarchy,JsonWriter.WriteToken()
, automatically converts all integer values tolong
.
Sample source with preliminary unit tests here.