Constructing a Rails ActiveRecord where clause

Question

What's the best way to construct a where clause using Rails ActiveRecord? For instance, let's say I have a controller action that returns a list of blog posts:

def index
  @posts = Post.all
end

Now, let's say I want to be able to pass in a url parameter so that this controller action only returns posts by a specific author:

def index
  author_id = params[:author_id]

  if author_id.nil?
    @posts = Post.all
  else
    @posts = Post.where("author = ?", author_id)
  end
end

This doesn't feel very DRY to me. If I were to add ordering or pagination or worse yet, more optional URL query string params to filter by, this controller action would get very complicated.

Answer 1

How about:

def index
  author_id = params[:author_id]

  @posts = Post.scoped

  @post = @post.where(:author_id => author_id) if author_id.present?

  @post = @post.where(:some_other_condition => some_other_value) if some_other_value.present?
end

Post.scoped is essentially a lazy loaded equivalent to Post.all (since Post.all returns an array immediately, while Post.scoped just returns a relation object). This query won't be executed until you actually try to iterate over it in the view (by calling .each).

Answer 2

Mmmh, the best approach you want to use can be to spread this in 2 actions

def index
   @post = Post.all
end

def get
  @post = Post.where("author=?", params[:author_id])
end

IMHO it has more sense if you think about a RESTful API, index means to list all and get (or show) to fetch the requested one and show it!