ASP.NET Core Web API Interview Question #39

How can you customize automatic validation responses?

DTOs, Model Binding, Validation & API Responses Junior Beginner

Quick Interview Answer

ApiBehaviorOptions can customize the response produced when model validation fails. This is useful when an organization requires a consistent error envelope, correlation identifier, or additional metadata.

Detailed Explanation

Customization should preserve meaningful HTTP semantics and enough field-level information for clients to correct invalid input.

Code Example

builder.Services.Configure<ApiBehaviorOptions>(options =>
{
    options.InvalidModelStateResponseFactory = context =>
    {
        var problem = new ValidationProblemDetails(
            context.ModelState);

        return new BadRequestObjectResult(problem);
    };
});