How to avoid calling ModelState.IsValid on every PostBack?

Question

I pretty much always want to check if ModelSate.IsValid is called when I do a postback. And having to check at the start of every post back violates the DRY principle, is there a way to have it checked automatically?

Example:

[HttpPost("RegisterUser")]
[AllowAnonymous]
public async Task<IActionResult> RegisterUser([FromBody] UserRegisterViewModel vmodel)
{
    if(!ModelState.IsValid)          // This code is repeated at every postback
        return ModelInvalidAction(); // Is there a way to avoid having to write it down?

    // do other things

    return StatusCode(201);
}

Answer 1

The framework provides an abstract ActionFilterAttribute that you can subclass.

You can use an action filter to automatically validate model state and return any errors if the state is invalid:

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Filters;

public class ValidateModelAttribute : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext context)
    {
        if (!context.ModelState.IsValid)
        {
            context.Result = new BadRequestObjectResult(context.ModelState);
        }
    }
}

You can either then use it on individual actions or register it globally

Reference Asp.Net Core : Action Filters

Answer 2

You can try something like this:

public class ValidateModelAttribute : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        if (!filterContext.ModelState.IsValid)
        {
            filterContext.Result = new BadRequestResult();
        }
    }
}

You can request any registered service like this filterContext.HttpContext.RequestServices.GetService<ILogger>(). You can decorate by action filter your action or controller:

[HttpPost("RegisterUser")]
[AllowAnonymous]
[ValidateModel]
public async Task<IActionResult> RegisterUser([FromBody] UserRegisterViewModel vmodel)
{
    ...
}