Web API translate JSON object into simple parameters - .net-core

Question

If I am sending JSON data (via POST) to a .Net Core Web API like this
{ a: "a", b: "b" }
What do I need to do to have a controller method like this?
[HttpPost]
public async Task SometMethod(string a, string b)
{
return Ok();
}
Normally, all tutorials and docs say that you need to define a class and use [FromBody] attribute. But how can I make do without extra classes that I don't really need?

Answer 1

Firstly,your json should be:
{
"a":"a",
"b":"b"
}
You could receive data as JObject instead of a class like below:
[Route("api/[controller]")]
[ApiController]
public class ValuesController : ControllerBase
{
[HttpPost]
public void Post(JObject data)
{
//get the property value like below
var data1 = data["a"].ToString();
var data2 = data["b"].ToString();
}
}
Result (For easily distinguish value and property name,I change a to aaa and b to bbb):

Answer 2

If you want to post the data to the method like this, you will have to serialize your data before you can send it to the server. Assuming you are using JQuery, you can do like the following.
var postData = $.param({ a: "a", b: "b" });
//Then you can send this postData obejct to the server. This should perfectly bound to the parameters.
You can also use the same in an angular app.

Answer 3

After some research I came up with ModelBinder to do just this. It is not performant since it re-parses the whole request body for every parameter. I will improve it in the future.
https://github.com/egorpavlikhin/JsonParametersModelBinder
public class JsonBinder : IModelBinder
{
public async Task BindModelAsync(ModelBindingContext bindingContext)
{
if (bindingContext == null) throw new ArgumentNullException(nameof(bindingContext));
var actionDescriptor = bindingContext.ActionContext.ActionDescriptor as ControllerActionDescriptor;
if (actionDescriptor.MethodInfo.GetCustomAttributes(typeof(JsonParametersAttribute), false).Length > 0)
{
var context = bindingContext.HttpContext;
if (context.Request.ContentType != "application/json")
{
bindingContext.Result = ModelBindingResult.Failed();
return;
}
#if (NETSTANDARD2_1 || NETCOREAPP3_0)
context?.Request.EnableBuffering();
#else
context?.Request.EnableRewind();
#endif
using var reader = new StreamReader(context.Request.Body, Encoding.UTF8,
false,
1024,
true); // so body can be re-read next time
var body = await reader.ReadToEndAsync();
var json = JsonSerializer.Deserialize<Dictionary<string, JsonElement>>(body);
if (json.TryGetValue(bindingContext.FieldName, out var value))
{
if (bindingContext.ModelType == typeof(string))
{
bindingContext.Result = ModelBindingResult.Success(value.GetString());
}
else if (bindingContext.ModelType == typeof(object))
{
var serializerOptions = new JsonSerializerOptions
{
Converters = {new DynamicJsonConverter()}
};
var val = JsonSerializer.Deserialize<dynamic>(value.ToString(), serializerOptions);
bindingContext.Result = ModelBindingResult.Success(val);
}
}
context.Request.Body.Position = 0; // rewind
}
}
}