What

Query string is a part of URL that specifies parameters and values. It’s most commonly used with GET request. But you can also append query string to other methods, like POST.

In Rails, these kind of parameters are called Query Parameters.

But for POST, data is sent within the request body. Since it’s not safe at all to append your bank information in the URL.

In Rails, these kind of parameters are called Request Parameters. Well, they are indeed more related to request, not URL.

Why

So what if for a POST request, when a query and a request parameter both have the same name but with different value, which will arrived at the controller action?

Good question.

I tried myself, found that query parameter will override request parameter of the same name.

How

Since Rails application is Rack-based, which means it will utilize Rack infrastructure, including parameters extraction.

For Rack, the latter one takes precedence, which is contrary to what I tried.

So the only possibility is that the logic is overridden by Rails.

Check here for details.

Where

This is a good story regarding how Rails is built upon Rack.

When

Who