Handling multiple filters (params) cleanly in controller

Question

I have a class called Post, and I need to be able to accommodate the following scenarios:

• If a user selects a category, only show posts from that category
• If a user selects a type, only show posts with that type
• If a user selects a category and type, only show posts from that category with that type
• If a user selects nothing, show all posts

I'm wondering if it's inevitable that my controller is just going to look gross with a ton of conditionals... here's my flawed approach at tackling this – does anyone know how I can accomplish this?

class PostsController < ApplicationController

  def index
    @user = current_user

    # If a user has not specified a type or category, 
    # show them everything
    @posts = Post.all

    # If a user has selected a category, but no type, only 
    # show posts from that category.
    if params[:category] && !params[:type]
      category = Category.find(params[:category])
      @posts = @category.posts
    end

    # If a user has selected a category and a type, only show
    # posts from that category with that type
    if params[:category] && params[:type]
      category = Category.find(params[:category])
      type = params[:type]
      @posts = category.posts.where(post_type: type)
    end

    # If a user has selected a type but not a category, show all 
    # of the posts with that type 
    if params[:type] && !params[:category]
      type = params[:type]
      @posts = Post.where(post_type: post_type)
    end
  end

end

Answer 1

You'll be better off following the convention of "fat models, skinny controllers", meaning you should put this kind of logic in the model itself. The Post class should be able to report which posts correspond to your conditions, so you can define a method to do that:

class Post < ActiveRecord::Base
  ...
  def self.by_category_and_type(category = nil, type = nil)
    return where(category: category, type: type) if category && type
    return where(category: category) if category
    return where(type: type) if type
    all
  end
  ...
end

Then in your controller you can just call

@posts = Post.by_category_and_type(params[:category], params[:type])

I haven't tested this, but I think it should do the trick. Let me know if it doesn't!

Answer 2

You can refactor your code a bit like this:

controller:

  def index
    @user = current_user
    @posts = find_posts 
  end

  private

  def category
    Category.find(params[:category])
  end

  def find_posts
    if type = params[:type]
      if params[:category]
        category.posts.of_type(type)
      else
        Post.of_type(type)
      end
    elsif params[:category]
      category.posts
    else
      Post.all
    end
  end

Add the scope to your Post model, name it as you like:

scope :of_type, ->(type) { where(post_type: type) }

I recommend you using https://github.com/voxdolo/decent_exposure The code above is not the best, but you can improve it with this gem. You can even create a new class which will be responsible for finding posts and use this class in your controler.