Json.Net - private setters

This post is a simple on explaining how you can make Json.Net handle private setters. I will show you three solutions but only one fullfills my requirements:

• No attributes should be required
• No fields should be serialized/deserialized only properties

Sounds easy. Lets dig in.

Update

The source NuGet package has been replaced by a new package that contains more resolvers and are distributed in binary from instead of source.

• NuGet: https://www.nuget.org/packages/JsonNet.ContractResolvers/
• Repo: https://github.com/danielwertheim/jsonnet-contractresolvers
• Old source package: This has been replaced with the package above. Old post about source package..

Alternative 1 - Using attributes

This solution fails on the requirement "No attributes should be required" but I will show it anyway. Using the JsonPropertyAttribute you can get private setters to be "supported" when deserializing.

[TestMethod]
public void When_it_is_decorated_with_attribute()
{
    var json = @"{""Name"":""Daniel""}";

    var entity = JsonConvert.DeserializeObject<Person>(json);

    Assert.AreEqual("Daniel", entity.Name);
}

public class Person
{
    [JsonProperty]
    public string Name { get; private set; }

    public void SetName(string name)
    {
        Name = name;
    }
}

Test Passed

Alternative 2 - DefaultContractResolver.DefaultMembersSearchFlags

This solution fails on the requirement "No fields should be serialized/deserialized only properties" but I will show it anyway.

[TestMethod]
public void When_member_search_flags_include_non_public()
{
    var contractResolver = new DefaultContractResolver();
    contractResolver.DefaultMembersSearchFlags |= BindingFlags.NonPublic;
    var settings = new JsonSerializerSettings
    {
        ContractResolver = contractResolver
    };
    var json = @"{""Name"":""Daniel""}";

    var entity = JsonConvert.DeserializeObject<Person>(json, settings);

    Assert.AreEqual("Daniel", entity.Name);
}

public class Person
{
    public string Name { get; private set; }

    public void SetName(string name)
    {
        Name = name;
    }
}

Test Passed

Alternative 3 - a custom contract resolver

This solution fulfils my requirements that I have in SisoDb of no attributes and only change the behaviour for private setters.

[TestMethod]
public void When_using_the_custom_contract_resolver()
{
    var contractResolver = new SisoJsonDefaultContractResolver();
    var settings = new JsonSerializerSettings
    {
        ContractResolver = contractResolver
    };
    var json = @"{""Name"":""Daniel""}";

    var entity = JsonConvert.DeserializeObject<Person>(json, settings);

    Assert.AreEqual("Daniel", entity.Name);
}

public class Person
{
    public string Name { get; private set; }

    public void SetName(string name)
    {
        Name = name;
    }
}

public class SisoJsonDefaultContractResolver
    : DefaultContractResolver
{
    protected override JsonProperty CreateProperty(
        MemberInfo member,
        MemberSerialization memberSerialization)
    {
        var prop = base.CreateProperty(member, memberSerialization);

        if (!prop.Writable)
        {
            var property = member as PropertyInfo;
            if (property != null)
            {
                var hasPrivateSetter = property.GetSetMethod(true) != null;
                prop.Writable = hasPrivateSetter;
            }
        }

        return prop;
    }
}

Test Passed

What it does is to extend the DefaultContractResolver and if the created JsonProperty isn't already marked as writeable and the member is a property and not a field, we check if there is a private setter for use.

That's it. Of course I wouldn't consume it like that every time, instead I would put it in an application specific abstraction that uses JSON.Net as a component.

//Daniel