ASP.NET Core MVC Interview Question #178

How would you prevent duplicate form submissions in an MVC application?

Senior Practical MVC Scenarios & Production Architecture Senior Advanced

Quick Interview Answer

Use the Post/Redirect/Get pattern so a successful POST redirects to a GET page instead of rendering the final page directly. For operations where duplicate execution would be harmful, also use server-side idempotency or uniqueness controls.

Detailed Explanation

PRG improves browser behavior but does not guarantee that two POST requests cannot reach the server. Critical payment, order, or booking workflows need server-side duplicate protection.

Code Example

[HttpPost]
public async Task<IActionResult> Create(OrderInputModel model)
{
    var result = await _service.CreateOnceAsync(
        model.RequestId, model);

    return RedirectToAction(
        "Details", new { id = result.Id });
}