Automatically bind pascal case c# model from snake case JSON in WebApi

Question

I am trying to bind my PascalCased c# model from snake_cased JSON in WebApi v2 (full framework, not dot net core).

Here's my api:

public class MyApi : ApiController
{
    [HttpPost]
    public IHttpActionResult DoSomething([FromBody]InputObjectDTO inputObject)
    {
        database.InsertData(inputObject.FullName, inputObject.TotalPrice)
        return Ok();
    }
}

And here's my input object:

public class InputObjectDTO
{
    public string FullName { get; set; }
    public int TotalPrice { get; set; }
    ...
}

The problem that I have is that the JSON looks like this:

{
    "full_name": "John Smith",
    "total_price": "20.00"
}

I am aware that I can use the JsonProperty attribute:

public class InputObjectDTO
{
    [JsonProperty(PropertyName = "full_name")]
    public string FullName { get; set; }

    [JsonProperty(PropertyName = "total_price")]
    public int TotalPrice { get; set; }
}

However my InputObjectDTO is huge, and there are many others like it too. It has hundreds of properties that are all snake cased, and it would be nice to not have to specify the JsonProperty attribute for each property. Can I make it to work "automatically"? Perhaps with a custom model binder or a custom json converter?

Answer 1

No need to reinvent the wheel. Json.Net already has a SnakeCaseNamingStrategy class to do exactly what you want. You just need to set it as the NamingStrategy on the DefaultContractResolver via settings.

Add this line to the Register method in your WebApiConfig class:

config.Formatters.JsonFormatter.SerializerSettings.ContractResolver =
    new DefaultContractResolver { NamingStrategy = new SnakeCaseNamingStrategy() };

Here is a demo (console app) to prove the concept: https://dotnetfiddle.net/v5siz7

---

If you want to apply the snake casing to some classes but not others, you can do this by applying a [JsonObject] attribute specifying the naming strategy like so:

[JsonObject(NamingStrategyType = typeof(SnakeCaseNamingStrategy))]
public class InputObjectDTO
{
    public string FullName { get; set; }
    public decimal TotalPrice { get; set; }
}

The naming strategy set via attribute takes precedence over the naming strategy set via the resolver, so you can set your default strategy in the resolver and then use attributes to override it where needed. (There are three naming strategies included with Json.Net: SnakeCaseNamingStrategy, CamelCaseNamingStrategy and DefaultNamingStrategy.)

---

Now, if you want to deserialize using one naming strategy and serialize using a different strategy for the same class(es), then neither of the above solutions will work for you, because the naming strategies will be applied in both directions in Web API. So in in that case, you will need something custom like what is shown in @icepickle's answer to control when each is applied.