How to handle nullable query parameters in ASP.NET Web API controllers

Other Questions API
1

I’m working on a Web API endpoint that needs to accept multiple optional query parameters. The URL structure should look like this:

/api/products?category=electronics&brand=samsung&price=500&color=black&year=2023

Any of these query parameters might be missing from the request. The client could send anywhere from zero to all five parameters.

I have this controller setup:

public class ProductsController : ApiController
{
    // GET /api/products?category=electronics&brand=samsung&price=500&color=black&year=2023
    public string GetSearchProducts(string category, string brand, string price, string color, DateTime? year) 
    {
        // processing logic here
    }
}

This worked fine in an earlier version but now I’m getting a 404 error when I don’t provide all the parameters. The error message says no matching action was found on the controller.

What’s the proper way to define the method signature so it accepts optional query string parameters without requiring URL routing configuration?

2

make all ur params nullable except the required ones. change string category to string category = null and do the same for the others. that DateTime should probably be int? year = null unless ur actually passing full dates. works every time for me.

3

That 404 happens because Web API treats non-nullable parameters as required route constraints. I hit this same issue last year building a product search endpoint. What fixed it was switching to a model-based approach instead of individual parameters. Create a simple class with nullable properties and use that as your single parameter. The model binder automatically populates whatever query parameters are present and leaves the rest null. Way cleaner than a method signature with five default parameters, and scales better when you add more filters later. Plus you get better intellisense and can add validation attributes if needed.

4

Web API needs all non-nullable parameters by default, so you’re hitting that wall. Make your parameters nullable with default values:

public string GetSearchProducts(string category = null, string brand = null, string price = null, string color = null, DateTime? year = null)
{
    // Your processing logic here
}

This lets you pass any combo of parameters or skip them completely. I’ve used this tons in my projects - works for everything without messing with routing. Just set strings to null as defaults and they become optional.