When you’re trying to make some controllers of your app tinier with agreement to have fatter models, you might think about scope or writing functions for that Model class. In this post, I wanna write some examples of that Active Record technique
Problem definition
The problem my rails app is about is:
-
- We have models:
User,PostandTag - User and Post have
1-nrelationship whilePostandTaghave then-nrelationship - We gonna find
Postwith many constraints relating toUserandTag - For
Post, we havestate:string
- We have models:
Before DRY
In the Post model, we have state as and is in ['draft', 'published'] . It’s is normal to query posts by state like
published_posts = Post.where(state: 'published') draft_posts = Post.where(state: 'draft')
How if you wanna check if a post published or not
post = Post.where(id: 1).first is_published = post.state == 'published'
And now I wanna get posts of some authors
posts = Post.joins(:authors).where(author_id: params[:author_ids])
or posts with some tag names
posts = Post.joins(:tags).where(tags: {name: params[:tag][:names]})
With some improvements
All are good now, right? hm, it could be even better if we can give some logic to our model
Like this
class Post < ActiveRecord::Base
STATES = ['published', 'draft']
belongs_to :author, :class_name => 'User', :foreign_key => 'author_id'
has_many :tags, through: :post_tags
scope :published, where(state: 'published')
scope :tag, lambda{|tags| joins(:tags).where(tags: {name: tags})}
STATES.each do |state_name|
define_method "#{state_name}?" do
self.state == state_name
end
end
end
Then, we can have
posts = Post.tag(params[:tags]).published post = Post .find(params[:id]) post.published?
Happy Coding!
Recently, I have add 
Colin Dao 