Question

Total Rails noob, working through the Rails Tutorial videos. I’m all the way to the last lesson, and there’s something I don’t understand:

@users = @user.followed_users.paginate(page: params[:page])

Specifically, the bit I’m not tracking on is paginate(page: params[:page]). I looked at the paginate docs and I understand the paginate method can take three params, :page being one of them. I think this parameter means “current page,” but the will_paginate docs say it defaults to 1.

I also know (think) that params[:page] refers to the built-in Rails params hash, meaning, current session params. Right?

So… I don’t get it. Why do I need it? How does the :page symbol get into the params hash? What does this really do?

For additional context, see listing 11.30 on the Ruby Tutorial book. Any help would be much appreciated.

Answer 1

I think what you might be misunderstanding is how Ruby arguments work in this case. paginate does not actually take 3 arguments, but instead takes a single hash argument with three options (key/value pairs).

In Ruby, when you pass key/value pairs as the last set of arguments, they are automatically converted to a hash. For example, the following are equivalent:

paginate({page: 1})

is the same as:

paginate(page: 1)

So really what you are doing is passing a single argument, which is a hash that has multiple key/value pairs.

Now to specifically answer your questions:

Why do I need it?

You need to pass this value in so that will_paginate knows which page you are currently on. It defaults to page one because on the initial page load, you will not have ?page=x in your URL. After you change to a different page, it takes the page value from the URL and passes that to the paginate method.

How does the :page symbol get into the params hash?

Any argument that is part of the query params in the URL will get automatically passed to the params hash by Rails (more likely Rack which Rails is built upon)

What does this really do?

I’m hoping the above answered this, but if not, maybe it provided you with enough info to come up with a more specific question.