Which has_many association to use?

Has and Belongs to Many Example Repo

Railscast 047 Two Many-to-Many prompted me to ask this. He showed an has_many_and_belongs_to and an has_many :through example. From what the episode, Ryan Bates seems to generally like has_many :through better because it adds flexibility. What are some of the reasons behind this conclusion?

Differences

The Rails Guides on Associations has a section about this.

For has_and_belongs_to_many the relationship is built through a join table using only two models. A has_many :through relationship creates a third model that belongs_to the two models in the relationship. The circumstances you would want a has_many :through association would be:

if you need validations, callbacks, or extra attributes on the join model.

A case where you might want to have a has_many :through associations would be if you have a feature of ‘following’ within the app. Each user has followers and following users. One relationship could be established, but both do not necessarily have to be established. In the case of followers and following users, you would actually need two relationship tables in the database. ActiveRecord provides the ability to ‘reverse’ a relationship based on what the foreign key is.

There could be a relationships table with follower_id and followed_id. To find a user’s followed users, then you would set the foreign key to the follower_id. To find a user’s followers, then you would set the foreign key to the followed_id and rename this relationship to something like reverse_relationship within the model.

Railscast 046 Catch All Route

The GitHub Repo
The Heroku App

This episode focused on creating a catch all route that redirects to a product’s page based on the partial route typed in. Example: /tele to /television

The routes syntax has been updated since the creation of the episode.

match '*path' => 'your_controller#your_action', via: :get

StackOverflow

You would want to create this catch all route at the bottom of your routes file because it would match all the requests coming into you Rails app otherwise. Because the match all routes redirects to the product page you actually are looking for, this isn’t that bad of an outcome.

After the route catches the input of the user from the route, it then calls the redirect#index. In this controller we can control the behavior of that route.

class RedirectController < ApplicationController
  def index
    if Rails.env.development? || Rails.env.test?
      product = Product.where('name LIKE ?', "#{params[:path].first}%").first
    elsif Rails.env.production?
      product = Product.where('name ILIKE ?', "#{params[:path].first}%").first
    end
    redirect_to product_path(product)
  end
end

In this controller I reused what I learned about PostgreSQL’s LIKE and ILIKE functions from the episode about Simple search forms to separate difference lines of code based on the environment.

There is a single action, index, that is called from the catch all route. We find where the product has a name that is similar to the partial parameter given in the route. We access this partial parameter through the params has with params[:path]. We also call first() to get the first value of the hash. If the user inputed /foo/bar/baz, then it would use the foo value only. Again from episode 037 simple search form, we use the SQL Wildcard % to match anything that starts with the partial route given. If there are multiple records that have the same partial route, then we call first() again at the end of the line to only retrieve the first record.

get '*path' => 'redirect#index'

Railscast 042 With Options

class User < ActiveRecord::Base
  with_options if: :should_validate_password? do |user|
    user.validates_presence_of :password
    user.format_of :password, with: /^[^\s]+$/
  end

  attr_accessor :updating_password

  def should_validate_password?
    updating_password || new_record?
  end
end

class Account < ActiveRecord::Baase
  with_options dependent: :destroy do |acc|
    acc.has_many :customers
    acc.has_many :products
    acc.has_many :invoices
    acc.has_many :expenses
  end
end

This is a convenient method to be aware of. When there are numerous records that have the same options, then using with_options could clean up the code and it more DRY.

The with_options() method accepts the options as the first argument, then it accepts a block for the model class. This argument is the object used to call the validations on. In the case of user, user.validates_presence_of :password does the normal presence validation, but adds the benefit of using the with_options() method.

Further Reading

http://apidock.com/rails/Object/with_options

Railscast 208 ERB Blocks in Rails 3+

GitHub Repo

Heroku App

I was originally going to create the episode 40 blocks in view, but there was a comment mentioning that episode 208 was the updated version. I did watch episode 40 nonetheless, and I noticed how much Rails has improved. The way to create a block in view in Rails 2 was by concatenating and using a block.binding. This seems like a hack compared today’s Rails standard.

For comparison the code for episode 40

def admin_area(&block)
  concat content_tag(:div, capture(&block), :class => 'admin'), block.binding if admin?
end

Episode 208

def admin_area(&block)
  content_tag(:div, :class => "admin", &block) if admin?
end

The line for the episode 208 was shorter because it eliminated concat capture() and block.binding. concat was rendered unnecessary after ERB used the <%= %> tag to signify whether or not the output would be rendered to the view. capture() tried to capture the output of a block’s yield. The content_tag now is able to accept a block as an argument without the need for capture(). block.binding binds to the erb templating. I’m not sure why this became unnecessary, but I suspect the revision of erb fixed this.

Assets Precompile

While pushing to Heroku the CSS I wrote for the admin_area was not being rendered. I eventually found the answer on StackOverflow. I did not have the rails_12factor gem. After further reading of the README for rails_12factor, rails_12factor allows static assets to be retrieved despite using a proxy like Nginx. A proxy like Nginx routes the asset path of assets/rails.png to public/assets/rails.png. Rails 4 is sort of encouraging the use of a CDN to host static assets. The Readme also linked to the ’12factor’ methodology which seems to touch on devops.

Railscast 038 Multibutton Form

The GitHub Repo

The Heroku App

What I love about following the Railscasts and actually implementing the small features is that making these apps are quick, I’m exposed to something I wouldn’t have been otherwise, and they are straightforward. This episode was no different.

preview_button

<%= submit_tag 'Preview', name: 'preview_button' %>

The Preview button is similar to the the submit button, but it differs in it function. The name for the button defaults to commit when using the submit_tag helper. This is good when you need to create a normal submit button to create or update a record, but in the case of a preview button, you do not want to save the record just yet. Instead of having the name='commit we override this default by specifying the name should be equal to preview_button. With the name now equalling preview_button the parameters hash has "preview_button" => "Preview".

Controller

def create
...
  respond_to do |format|
    if params[:preview_button] || !@project.save
      format.html { render action: 'new' }
      format.json { render json: @project.errors, status: :unprocessable_entity }
    else
      format.html { redirect_to @project, notice: 'Project was successfully created.' }
      format.json { render action: 'show', status: :created, location: @project }
    end
  end
end

We can then use the params[:preview_button] within our conditional in the create action. If params[:preview_button] is not nil, then the controller will redirect to the new view while still having the preview_button parameter present in the URL. If there is no params[:preview_button] defined, then we know that the form was submitted through the normal submit button and not the preview button.

Textilize

<% if params[:preview_button] %>
  <div id="preview">
    <h2><%= @project.name %></h2>
    <%= textilize @project.description %>
  </div>
<% end %>

When we are redirected to the new view, the params[:preview_button] is still defined. We can use this in another conditional within our view to display a preview. Here we are previewing the project’s description using the textilize text helper. This was deprecated back in Rails 2, but I found a gem that dropped in to Rails 3+ that adds this back. There has to be a reason that the Rails Core Team deprecated this, so I do not plan to use this again. Instead I might reuse the code I used to render markdown to the view from my Markdown Todo List Rails API App

Railscast 037 Simple Search Form

The GitHub Repo

The Heroku App

Form

<%= form_tag projects_path, method: :get do %>
<p>
  <%= text_field_tag :search, params[:search] %>
  <%= submit_tag 'Search', name: nil %>
</p>
<% end %>

The form for the search form has many lessons to learn. The use of form_tag over form_for is preferred we are not updating attributes associated with a specific model. Here the form_tag submits to the projects path. Normally when you submit a form using the form_for or form_tag Rails helper Rails create the html tags with a post method filled in. When you submit a post request to the projects path, Rails thinks you are trying to create a new record because of the RESTful design. To counteract this you have to explicitly specify the method used on this form, in this case get.

Controller

def index
  @projects = Project.search(params[:search])
end

Instead of the usual Project.all, we use a search method that we defined in the project model. The search method accepts a argument that is matched with records in the database.

Model

class Project < ActiveRecord::Base
  def self.search(search)
    if search
      if Rails.env.development?
        where("name LIKE ?", "%#{search}%")
      elsif Rails.env.production?
        where("name ILIKE ?", "%#{search}%")
      end
    else
      all
    end
  end
end

This is where most of the work is being done. Here we are defining a class method called search which accepts one parameter. If this parameter is true, then it will search for a name similar to the search argument. There is a conditional based on the environment because the LIKE function in SQLite3 used in development is case insensitive, while the LIKE function in PostgreSQL used in Production is case sensitive. PostgreSQL LIKE To counteract this, I have included the ILIKE function for only the production environment.

The "%#{search}%" confused me, so I asked on StackOverflow about what the % was. Apparently it is SQL Wildcards used to match characters in a string. It is similar to how Regex pattern matches, but SQL Wildcards are much simpler. It appears there are only four syntaxes that can be used. %, _, [], [^]. The % substitute zero or more characters. _ substitutes a single character. [] matches sets or ranges of characters. Example: [abc]% matches anything that starts with abc. Similar to regex you use ^ to declared not. [abc]% matches anything that does NOT start with abc. Similar to Regex, so this was not too mind blowing. The tricky part was learning the syntax used.

Emacs Ruby on Rails Mode: Rinari

I have been developing with Ruby on Rails and Emacs for a good three months now, but I haven’t been using the emacs editor to its full potential. Nothing illustrates that more than not using a Ruby on Rails minor mode like Rinari. I just enabled rinari-minor-mode today and watched the introduction Rinari Screencast, and I’m blown away at how much time I could be saving using come of the commands shown.

You could switch over to the controllers, models and views using the c-c ; f c, m, or v command keys. What I was really looking for was to make the erb <%= %> tags, and the rinari minor mode can do that as well with c-c ' e.

Cheatsheet

 C-c ; f c  rinari-find-controller
 C-c ; f e  rinari-find-environment
 C-c ; f f  rinari-find-file-in-project
 C-c ; f h  rinari-find-helper
 C-c ; f i  rinari-find-migration
 C-c ; f j  rinari-find-javascript
 C-c ; f l  rinari-find-plugin
 C-c ; f m  rinari-find-model
 C-c ; f n  rinari-find-configuration
 C-c ; f o  rinari-find-log
 C-c ; f p  rinari-find-public
 C-c ; f s  rinari-find-script
 C-c ; f t  rinari-find-test
 C-c ; f v  rinari-find-view
 C-c ; f w  rinari-find-worker
 C-c ; f x  rinari-find-fixture
 C-c ; f y  rinari-find-stylesheet
C-c ; s    rinari-script              
C-c ; e    rinari-insert-erb-skeleton 
C-c ; r    rinari-rake                
C-c ; w    rinari-web-server          
C-c ; x    rinari-extract-partial     
C-c ; ;    rinari-find-by-context     
C-c ; d    rinari-cap
C-c ; q    rinari-sql
C-c ; t    rinari-test
C-c ; c    rinari-console
C-c ; g    rinari-rgrep
C-c ; p    rinari-goto-partial
C-c ; '    rinari-find-by-context

more bindings can be seen with c-h b. I just learnt about this command through the Rinari video. It is useful because you can see all the commands associated to different minor modes.

Railscast 035 Custom REST Actions

The GitHub Repo

The Heroku App

This is one of those episodes I needed to see. I haven’t had to use the collection or member blocks in the routes file before, but I’m glad to know what they mean now. member and collection allows the developer to create custom RESTful routes that extends the rails conventions. A member route appends after the /:model/:id, so the controller action has the params[:id]. A collection route appends after the /:model route.

Examples of these two were the routes created in this episode.

resources :tasks do
  get 'completed', on: :collection
  put 'complete', on: :member
end

This creates the normal RESTful Rails routes, but it also create two custom routes. /tasks/completed/ and /tasks/:id/complete. The Rails Guides for Routing was useful for further reading.

TasksController

def completed
  @tasks = Task.where(completed: true)
end

def complete
  @task.update_attribute :completed, true
  flash[:notice] = 'Task Completed'
  redirect_to completed_tasks_path
end

The two custom actions were completed and complete The completed action returns a tasks instance variable where completed is true. The complete action updates an attribute to true, then redirects to the completed tasks view with a flash notice.

To complete a task, the episode shows creating a link with the put method being sent the complete_task_path while sending the task’s id.

Heroku Issue

For some reason when I tried to click on this ‘complete task’ link, heroku is giving me a ‘page doesn’t exist’ error. Locally the link works however. I have opened a StackOverflow question about the issue. I don’t think you need a view for that action because it redirects to the completed_tasks_path. Even the rake routes show a PUT for /tasks/:id/complete. I did discover that the Rails core team has been switching over to the Patch verb over the put http verb. This adheres to RFC specification for partial updates. Even though I tried to change out put for patch, I was unable to get this link working.