SnakeCase QueryParams .Net Core

The problem is that QueryParams Objects are not snake case

        public async Task<IActionResult> Search (
        [FromQuery] ProjectFilterDto filterParams,
        [FromQuery(Name = "page_size")] int pageSize = 10,
        [FromQuery(Name = "page_index")] int pageIndex = 0)

All other things, FromBody and Response are in snake case syntax

StartUp;

options.SerializerSettings.ContractResolver = new DefaultContractResolver()
{
  NamingStrategy = new SnakeCaseNamingStrategy(true, true)
};

is there any way to make query params like ProjectFilterDto to be snake case without using FromQuery(Name="x")?

Start out by creating an extension method that converts a given string to a snake cased version of it. We will need this method in the next step.

public static string ToSnakeCase(this string s)
{
    if (string.IsNullOrWhiteSpace(s))
    {
        return s;
    }

    s = s.Trim();

    var length = s.Length;
    var addedByLower = false;
    var stringBuilder = new StringBuilder();

    for (var i = 0; i < length; i++)
    {
        var currentChar = s[i];

        if (char.IsWhiteSpace(currentChar))
        {
            continue;
        }

        if (currentChar.Equals('_'))
        {
            stringBuilder.Append('_');
            continue;
        }

        bool isLastChar = i + 1 == length,
                isFirstChar = i == 0,
                nextIsUpper = false,
                nextIsLower = false;

        if (!isLastChar)
        {
            nextIsUpper = char.IsUpper(s[i + 1]);                    
            nextIsLower = !nextIsUpper && !s[i + 1].Equals('_');
        }

        if (!char.IsUpper(currentChar))
        {
            stringBuilder.Append(char.ToLowerInvariant(currentChar));

            if (nextIsUpper)
            {
                stringBuilder.Append('_');
                addedByLower = true;
            }

            continue;
        }

        if (nextIsLower && !addedByLower && !isFirstChar)
        {
            stringBuilder.Append('_');
        }

        addedByLower = false;

        stringBuilder.Append(char.ToLowerInvariant(currentChar));
    }

    return stringBuilder.ToString();
}

Now we can create a custom value provider that looks for snake cased query parameters using the ToSnakeCase() extension method we defined above.

public class SnakeCaseQueryValueProvider : QueryStringValueProvider, IValueProvider
{
    public SnakeCaseQueryValueProvider(
        BindingSource bindingSource, 
        IQueryCollection values, 
        CultureInfo culture) 
        : base(bindingSource, values, culture)
    {
    }

    public override bool ContainsPrefix(string prefix)
    {
        return base.ContainsPrefix(prefix.ToSnakeCase());
    }

    public override ValueProviderResult GetValue(string key)
    {
        return base.GetValue(key.ToSnakeCase());
    }
}

We also have to implement a factory for our value provider:

public class SnakeCaseQueryValueProviderFactory : IValueProviderFactory
{
    public Task CreateValueProviderAsync(ValueProviderFactoryContext context)
    {
        if (context == null)
        {
            throw new ArgumentNullException(nameof(context));
        }

        var valueProvider = new SnakeCaseQueryValueProvider(
            BindingSource.Query,
            context.ActionContext.HttpContext.Request.Query,
            CultureInfo.CurrentCulture);

        context.ValueProviders.Add(valueProvider);

        return Task.CompletedTask;
    }
}

The only thing left to do is to register the value provider in the ConfigureServices method in the Startup class.

public void ConfigureServices(IServiceCollection services)
{
    services
        .AddMvc(options =>
        {
            options.ValueProviderFactories.Add(new SnakeCaseQueryValueProviderFactory());
        }) 
        .AddJsonOptions(options => options.SerializerSettings.ContractResolver = new DefaultContractResolver
        {
            NamingStrategy = new SnakeCaseNamingStrategy()
        });
}

Hope this helps!

I've written a blog post about it all here: http://www.sorting.se/enable-snake-cased-query-parameters-in-your-restfull-asp-net-core-web-api/