JsonSerializerSettings to change case of property name but not name of property's property

Question

I am using below settings for camel casing of my class property.

JsonSerializerSettings settings = new JsonSerializerSettings()
        {
            ContractResolver = new Newtonsoft.Json.Serialization.CamelCasePropertyNamesContractResolver()
        };

Some of the property in the object are of some other class type. I do not want to change case of those properties.

Eg:

Public Class CaseToChange
{
    public string StringProperty{get;set;} //Change to camelCase
    public SomeOtherType OtherTypeProperty{get;set;} //Change name of this to camelCase but not property name of "SomeOtherType"

}

How to achieve this with JsonSerializerSettings?

Answer 1

If you can modify your types to add Json.NET serialization attributes, the easiest thing to do would be to add [JsonObject(NamingStrategyType = typeof(CamelCaseNamingStrategy))] to your CaseToChange type:

[JsonObject(NamingStrategyType = typeof(CamelCaseNamingStrategy))]
public class CaseToChange
{
    public string StringProperty { get; set; } //Change to camelCase
    public SomeOtherType OtherTypeProperty { get; set; } //Change name of this to camelCase but not property name of "SomeOtherType"
}

(Or, if you are using a version of Json.NET earlier than 9.0.1, add [JsonProperty("camelCaseName")] to each property as in this answer.)

If you cannot modify the type and must camel-case the properties of CaseToChange only through serializer settings, you can create a custom contract resolver that returns camel-cased names for CaseToChange and unmodified names for other types. The following does the trick:

public class OverrideContractResolver : ContractResolverDecorator
{
    readonly Dictionary<Type, IContractResolver> overrides;

    public OverrideContractResolver(IEnumerable<KeyValuePair<Type, IContractResolver>> overrides, IContractResolver baseResolver)
        : base(baseResolver)
    {
        if (overrides == null)
            throw new ArgumentNullException();
        this.overrides = overrides.ToDictionary(p => p.Key, p => p.Value);
    }

    public override JsonContract ResolveContract(Type type)
    {
        IContractResolver resolver;
        if (overrides.TryGetValue(type, out resolver))
            return resolver.ResolveContract(type);
        return base.ResolveContract(type);
    }
}

public class ContractResolverDecorator : IContractResolver
{
    readonly IContractResolver baseResolver;

    public ContractResolverDecorator(IContractResolver baseResolver)
    {
        if (baseResolver == null)
            throw new ArgumentNullException();
        this.baseResolver = baseResolver;
    }

    #region IContractResolver Members

    public virtual JsonContract ResolveContract(Type type)
    {
        return baseResolver.ResolveContract(type);
    }

    #endregion
}

Then serialize with settings as follows:

var settings = new JsonSerializerSettings
{
    ContractResolver =
        new OverrideContractResolver(
            new Dictionary<Type, IContractResolver> { { typeof(CaseToChange), new Newtonsoft.Json.Serialization.CamelCasePropertyNamesContractResolver() } },
            new Newtonsoft.Json.Serialization.DefaultContractResolver()),
};

And the resulting JSON will look like:

{
  "stringProperty": "string property",
  "otherTypeProperty": {
    "FooProperty": "foo",
    "BarProperty": 101
  }
}

Sample fiddle.

For optimal performance you may want to cache instances of the contract resolver.