Archives For MVC

In my previous post, Ruby Version Manager (RVM) Overview for Rails Newbs, I outline RVM’s architecture and fundamental features. That post is also very focused on RVMs role when running rails new.

BeforeAfterToday, I’d like to cover a few more common scenarios Rails developers will encounter after the initial install of RVM. More to the point though, we’ll be focused on how RVM can be used to optimize workflow in these scenarios.

In my own development journey, it wasn’t initially clear to me when I should be creating new gemsets. If you too have pondered this question, here’s my suggested answer…create a new gemset for every project you are working on. This approach is not only clean and orderly but more importantly reduces the chance that gem dependency errors sidetrack your work.

As a refresher, here’s the necessary commands to create and use a new gemset:

$ rvm gemset create new_gemset_name

$ rvm gemset use new_gemset_name

Hopefully you’re starting to get some clarity on the use-cases for global, default, and custom gemsets. Basically, global and default are largely used to influence what you get from rails new. Custom gemsets are then used to manage all gems related to a project from that point forward.


Like all devs, I’ve got lots of active projects in various stages on maturity on my machine.  Before I came across this little nugget of knowledge (just keep reading!), I was frequently running:

$ rvm use ruby_version_here

and then

$ rvm gemset use gemset_name_here

It worked pretty well, but when moving between projects in my command line I often got gem-related errors when trying to run rails s or rails c. The problem was that if I forgot to tell RVM to change gemsets when I moved across projects in my command line, the gems that project expected to be available weren’t there.

Before I get to the solution here, humor me with a quick aside…

In a previous life, I was an Excel junky. I really loved Excel and what it could do. Just like development, it offers an incredible combination of logic and creativity. Also like development, the mouse is not necessarily your friend. Learning to do things without leaving the keyboard can be a HUGE time saver. People who were more mouse-dependent would sometimes look over my shoulder as I worked and say, “dude, you need to teach a class on Excel!”. It was a nice compliment and while I was interested in sharing both my love of Excel as well as its features, I would often respond with,

“if you are ever working in Excel and thinking ‘there has to be a better way to do this’. There is. You just need to figure it out.”

The point is that even though I espoused awareness of this phenomena in the context of Excel, I lamely continued with my error-prone use of RVM for some weeks. It wasn’t until my good friend @megharastogi noticed what I was doing and said, “why don’t you use an .rvmrc file?”.

Eureka! An .rvmrc file sits at the root level of your application and basically tells RVM which Ruby version and gemset to use. RVM is smart and interprets these files as you navigate project folders in the command line.

Below is an actual .rvmrc file in one of my apps. It’s stored at your_project_name/.rvmrc or in the below case social-playlist/.rvmrc.

Screen Shot 2013-08-26 at 8.15.50 AM

Your .rvmrc file should be in the same location as your .gitignore, Gemfile, and README.

Boom! No more gem-related errors. Time saved. Happy dev.

If you haven’t yet, at some point you’ll clone an existing repo. After doing so, likely your first task is to ensure you can get the app running locally in your development environment. For a Rails app, having the required gems present locally is a critical step in the process.

While you’ve cloned the repo, the repo likely doesn’t contain the actual gems. It merely contains a statement of what gems are necessary, via the Gemfile.

Here’s my recommended order of operations:

1. Review the repo’s README file.

2.  Check the Gemfile of the target repo to see if a Ruby version and or gemset name is explicitly stated. (If it’s a Rails app, a Rails version will surely be stated).

3. Check the target repo for a .rvmrc file at project_directory/.rvmrc. If yes, this often also tell you which version of Ruby as well as the gemset name being used.

NOTE:  As per the Typical RVM Project Workflow, other potential locations where Ruby version and/or gemset dependencies may be stated include files named: .versions.conf, .ruby-version.

4. If a Ruby version is explicitly stated, ensure that Ruby version is installed locally on your machine with $ rvm list

a. If that version is already installed locally on your machine, make it active with $ rvm use ruby_version_here and go to step 5.
b. If that version is not installed locally on your machine, get it with $ rvm install ruby_version_name                                       c. If no version of Ruby is explicity stated, I recommend using the latest stable version.
d. Make the target version of Ruby active with  make it active with $ rvm use ruby_version_here

5. Run $ git clone target_repo_location_here

Note: Both of the above commands clone the same repo, they just use different security protocols. For the truly adventurous reader, here’s a deep dive on the hows and whys of each protocol.

6. $ cd newly_created_directory_name

7. $ rvm gemset create new_gemset_name

Note: If the repo already contained a .rvmrc file with a gemset name, consider naming your local gemset the same as what’s being used by the other dev(s) pushing to the repo.

8. $ rvm gemset use new_gemset_name

9. $ bundle install

If no .rvmrc file is already present in the app, create one! It’s up to you if you include the .rvmrc in the .gitignore (I strongly suggest you do not! This as an important file for ensuring consistency across collaborators).

While not RVM specific, for good measure I’ll also offer up the other following steps to get the newly cloned app running locally.

10. $ rake db:create

11. $ rake db:migrate

12. $ rake db:seed (optional – only run if seeds.rb contains seed data).

Unless there’s database or server specific requirements, that should suffice to get the app running locally with rails s.

Looping back to the big picture before closing out on this topic. Now we have a distinct gemset just for this project (meeting the objectives of best practice #1) – and automated instructions for RVM to use this gemset whenever this project is active (meeting the objectives of best practice #2) in the command line. And we can be confident we are mirroring the Ruby and Ruby gem configuration of the other devs on the project.

In my other post, Reading Rails 4: MVC and Scaffolding for Rails Newbs, I go deep on some of the code generated when running rails generate scaffold.

My original title and concept for the post was not Rails-version specific. I thought it would mostly be about MVC and scaffolding – but be agnostic of Rails version. However, by reviewing the output of rails new and rails scaffold (while having RVM use Rails 4), I quickly and easily learned a lot about Rails 4 versus the Rails 3 versions I was more familiar with.

The point here is that RVM (combined with rails generators), is your assistant in having multiple boilerplate/clean versions of working Rails apps side-by-side on your machine. This makes it easy to access, evaluate, compare, and understand fundamental changes in Rails versions. Personally, I found reviewing the output of a Rails 4 scaffold more educational on mass-assignment in Rails 4 than any online documentation.

If helpful, here’s specifically what I’m suggesting. Say you’ve been hesitating getting onto the Rails 4 bandwagon because you are up and running and proficient in Rails 3. Maybe you feel too busy right now to slow down and learn the “gotchas” in Rails 4. Well, I think 5 minutes spent on the following will probably get you past that hurdle

  1. Create a new gemset called “rails4scaffold” with $ rvm gemset create rails4scaffold
  2. Make the new gemset active with $ rvm gemset use rails4scaffold
  3. Install Rails 4 in that gemset by running $ gem install rails 4
  4. Create a new app by running $ rails new rails4scaffoldapp
  5. Scaffold a basic MVC in that app with rails generate scaffold books title author
  6. Run rake db:migrate
  7. Now go inspect key files like app/controllers/books_controller.rb and run $ rake routes to see how Rails 4 handles basic CRUD.

If you haven’t yet, consider moving Rails 4 into your default gemset!

As always, I really appreciate you reading my post. I hope it’s been useful for you in getting more value out of RVM. Your comments and feedback are welcomed.

One other quick point is that there are other tools and approaches for doing what RVM does (quite well in my opinion). However my goal is not to promote RVM, but to promote knowledgeable, confident, and satisfying development experiences. As such, I want to share a post titled “Vendor Everything” Still Applies by Ryan McGreary. In it, he makes some interesting and compelling arguments for an alternative approach to gemsets and gem management.

I’m personally still using RVM, but that doesn’t mean I will forever.

Truth fears no questions.
-Napoleon Bonaparte

Reading between the lines of Mr McGreary’s post as well as some of the comments, I think the main point is that consistency in approach to gemset management within a collaborating group is critical to developer happiness and productivity.

Here’s some of my other posts you might like:


In my previous post Top 10 Gems for new Rails Devs, I covered both the Devise and Twitter Bootstrap gems. Each of these gems is great at what they respectively do (authentication, design/styling). In this post, I’ll bring @plataformatec and @seyhunak‘s gifts together and easily put Devise sign-in and sign-up forms into Twitter Bootstrap modals.


What is a modal? If you aren’t familiar with modals, they are basically “pop-ups” or “prompts” that take a priority position in the user experience. If you’re interested in more theory regarding when and how to use modals, check out this post.

Getting sign-in and sign-up modals working in your application is not only a great introduction to using modals, but I think this feature creates a quality “first impression” for site visitors as well.

Want to see this code in a working repo? I’ll be orienting this post around a working implementation of this feature at This is a site I built with my good friend @lostincode. The project is open-source, so if you want to see everything in-context you can do so at

Okay, let’s get started…

Partials are basically re-usable pieces of code falling into the the View portion of MVC. (For a Rails 4-specific explanation for MVC, check out my other post Reading Rails 4: MVC and Scaffolding for Rails Newbs.

Partials in Rails are easily identifiable based on the preceding underscores _ in file names (Example: _partial.html.erb). If you’ve ever run a rails g scaffold, you’ve created a partial named _form.html.erb. This single form is used in both the new and edit views for your scaffolded model. Whether you are creating a new record in the database or editing an existing record, you likely want access to all the same fields. Given the overlap, a single partial can serve in both conditions.

Okay, now let’s build modal partials for today’s feature…

We’re going to need to create some new files and there’s no hard requirements about where they go in your app. I think you definitely want them somewhere in your app/views/ hierarchy, but exactly where after that is up to you.

In many of my projects I use a “welcome controller” and associated views for things like the home page or “about us” page. As such, I think app/views/welcome/ makes a great spot for the below two files.



Here’s a copy-paste of what I place into each file:


<div class="modal hide fade in" id="login">

<div class="modal-header">

<button class="close" data-dismiss="modal">x</button>

<h2>Sign in</h2>


<div class="modal-body">

<%= form_for(resource, :as => resource_name, :url => session_path(resource_name)) do |f| %>

<div><%= f.label :email %><br />

<%= f.email_field :email, :autofocus => true %></div>

<div><%= f.label :password %><br />

<%= f.password_field :password %></div>

<% if devise_mapping.rememberable? -%>

<div><%= f.check_box :remember_me %> <%= f.label :remember_me %></div>

<% end -%>

<%= f.submit "Sign in", :class => 'btn btn-small btn-success' %>

<% end %>


<div class="modal-footer">

<%= render "devise/shared/links" %>



Newb Note! The studious reader will have identified a sub-partial embedded within the partial we just created. Inspect the following statement:

<%= render "devise/shared/links" %>

That’s calling a partial into our partial! Don’t worry if you don’t fully understand just yet, it will all get clearer before we’re done.

Let’s get back to building our own partials. The second and final file we’ll need to create is:


<div class="modal hide fade in" id="sign_up">

<div class="modal-header">

<button class="close" data-dismiss="modal">x</button>

<h2>Sign Up</h2>


<div class="modal-body">

<%= form_for(resource, :as => resource_name, :url => registration_path(resource_name)) do |f| %>

<%= devise_error_messages! %>

<div><%= f.label :email %><br />

<%= f.email_field :email, :autofocus => true %></div>

<div><%= f.label :password %><br />

<%= f.password_field :password %></div>

<div><%= f.label :password_confirmation %><br />

<%= f.password_field :password_confirmation %></div>


<div class="modal-footer">

<p><div><%= f.submit "Sign up", :class => 'btn btn-small btn-success' %></div></p>

<p><a href="#" class="btn btn-small" data-dismiss="modal">Close</a></p>


<% end %>


NEWB NOTE! When creating modals in Twitter Bootstrap, make sure to use their built in classes for header, body, and footer. These control margins/padding that help things look just right.

Okay, back to business. Let’s get those partials working for us.

Remember above when I highlighted the partial-within-a-partial? The sub-partial was invoked using:

<%= render "devise/shared/links" %>

The reason I belabor the point is to establish a universal trend – and here it is…To render any partial, simply call render along with the location of the partial.

In our case, we have sign-in and sign-up buttons in the navbar on every page of our web site. As is the Rails way, we place app-wide View content in app/views/layouts/application.html.erb. Similarly, we want our new pop-up modals available (visible or not) on every page of our site. Accordingly, we put the below code into app/views/layouts/application.html.erb also:

<%= render "welcome/login_modal" %>

<%= render "welcome/sign_up_modal" %>

Newb Note! You might be thinking, “hey, that looks like a typo…aren’t partials pre-fixed with an underscore like _partial.html.erb ?” That’s not a typo, that’s simply the Rails convention for refering to partial location. Also, we do not need to supply the app/views/ elements of the directory path when refering to the location of partials. Rails confidently expects them to be in the V of MVC!

Where exactly should this render code be placed in app/views/layouts/application.hmtl.erb? Again, there’s not much of a hard and fast rule. Personally, I put mine immediately under the  <body> open div.

We’re not leaving app/views/layout/application.html.erb yet. Now we need to update our sign-in and sign-up buttons to engage our newly created modals as opposed to their historical forms. We can do this by simply changing the relevant link_to‘s to look like the below.

<%= link_to "Login", "#login", "data-toggle" => "modal", :class => 'btn btn-small' %>

<%= link_to "Sign up", "#sign_up", "data-toggle" => "modal", :class => 'btn btn-small btn-success' %>

Newb Note! The first time I implemented this feature, I placed the above code next to the existing link_to‘s. I did this to make sure everything was working with the new before getting rid of the old way.

One of the critical pieces of any link_to is the second argument – in our case, #login and #sign_up. The values provided here must match the id in the parent <div> of the associated partials. To make sure I’m clear, the relevant code from the parent <div>s are shown here again.

<div class="modal hide fade in" id="login">

<div class="modal hide fade in" id="sign_up">

Everything is just about ready to rock. When I first got this working in my app, I was disappointed that while the modals were popping up, they were dark like the subordinated background. Luckily, this StackOverflow post suggested adding the below into app/views/layouts/application.html.erb

<script type="text/javascript"> $(function ()

{ $("#myModal").modal({show:false }); </script>

If you’re like me, you’re thinking “where exactly should I put that code?”. Kindly the SO post also suggests putting it “right before the </head >” close tag.

Okay, so we’ve forms that users want to see. We’ve established a call to render them on every page of our application – next we need to make sure a new resource (the Devise term for user) is instantiated when our modal is engaged.

Thankfully the esteemed Pablo who originally wrote this entry (the birthplace of some succinctly powerful methods and now hosted on the official Devise wiki), provides us the below helper methods to place in app/helpers/application_helpers.rb.

def resource_name



def resource

@resource ||=


def devise_mapping

@devise_mapping ||= Devise.mappings[:user]


You’re done! Fire up a rails s and check it out in the browser before you git push.

Hopefully you’ve enjoyed and found value in this post. If so, drop me a comment or a tweet @mxstrand! Also, here’s a few other posts you might like:

Thanks for reading.

Even with all the great, often free resources on the web for open source developers, I know from personal experience that sometimes it can all be a little overwhelming  and confusing for newbs. While the information is meant to help, there’s so much of it! It’s sometimes hard to intuit the connections between the different pieces of the puzzle. I wrote my last post, Ruby Version Manager (RVM) for Rails Newbs to help in the first few hours of being a Rails dev. I’ve written this post in the hopes that it helps Rails newbs in their first week as a Rails dev.

Screen Shot 2013-08-24 at 2.04.51 AMHaving begun my journey as a Rails web developer only a few months ago, I remember the dichotomy of emotion I felt while working through tutorials like RailsCasts (Bates), Ruby on Rails Tutorial (Hartl) or Rails in Action (Biggs, Katz).  On one hand I was proud that I could mostly complete the exercises with working code, but on the other hand I felt like a fraud as I only understood 20% of what I was typing.  More experienced devs told me that this was the process and that I was learning even if it didn’t always feel like it.  In retrospect, I now know that was true – but it was painful at times.

Don’t misunderstand me, my learning journey isn’t over. I’ve quickly come to see this rabbit-hole may have no end. Depending on the topic, I still often only understand 20% of what I’m reading or typing. The good news is that I’ve become more comfortable in this state. I no longer feel like a fraud. I feel like what I am – someone on a learning path.

“Life is a journey, not a destination.” -Ralph Waldo Emerson

Okay, with that prologue out of my system – the point is that if you are similarly finding yourself in the early stages of your Rails journey, I wanted to offer up my own newb-inspired, highly simplified, explanation of MVC and some of the basic code provided in a Rails scaffold.  Here we go!

Think of a Rails web app as a database of information that sits on the internet. If you allow them, anyone with internet access and a web browser can visit your database to perform 2 tasks:

  1. Look at the information in the database
  2. Put additional information in the database

That’s it. That’s the whole enchilada. But of course, let’s break that down further.

Newbs can think of Model – View – Controller (MVC) as a commonly-agreed best practice in how to organize web application logic. This means code performing certain functions go in the Model, code of an alternate purpose goes in the Controller…you get the idea. Each of the components is described below.

Newb Note! MVC is not a Rails-specific practice. Learning it in the context of Rails will provide a foundation to accelerate your learning of other frameworks like iOS.

Model:  The model defines the architecture and logic of the “database on the internet” described above. Assuming a classical relational database, the newb can think of a database as one or more “tables”, each table looking like a spreadsheet – a matrix formed by columns and rows. For example, let’s consider a table containing a list of books. In this list, for each book we store it’s title and author. As such, title is one column and author is another column.  Because it’s a database, we also assign each book in the list a unique numerical identifier (this is commonly known a “primary key”).  So we’ve got three columns: numerical ID, title, and author.  Each row in the list is called a “record”. In summary, the Model defines the database characteristics – but it is not the actual data. Because the database is clearly defined in the Model, its data is accessible to the Controller (the “C” in MVC). But before we talk about Controllers, let’s discuss the View.

View: So we’ve got a database on the internet, but databases aren’t built for their looks. Databases are just raw information. Take our books list example. Maybe the user only wants to see a list of books by John Grisham. If they went to our single database table, they’d have to figure out a way to ignore all the books not by John Grisham. In a long list, this could be a pain. Even while this might meet their needs one time, I doubt our database would be their favorite place to look at book information. Users deserve better. As such, we use “Views” to create a friendly and intuitive way for people to both look at and put information in the database.

Controller: In my opinion, M-V-C should be changed to M-C-V.  Why? Well, because the “C” or the “Controller” conceptually sits between the Model and the View. Remember what was said in the Model description above,

Because the database is clearly defined in the Model, it’s data is accessible to the Controller.

The controller translates the different types of the user’s 2 main instructions communicated through the View (reminder on those instructions below) into something the database understands.

  1. Show me some information from the database
  2. Put additional information in the database

Conversely, when appropriate and the database provides the controller raw data in response to the user’s request, the controller readies the data for presentation in the View.

Okay, this all sounds simple enough.  Let’s get into some code.

Screen Shot 2013-08-25 at 11.49.01 AMPart of the power of Rails comes from its “generators“. Because Rails is built on the below premise,

“most web apps are simply a database sitting on the internet waiting for anyone with a web browser to come look at the information in the database or put additional information in the database”

Rails gives web developers “generators” to create a lot of free code supporting the above scenario.  The newb will likely not be surprised to hear that there are generators for each component of the MVC.  For example:

$ rails generate model will create a skeleton for a database table and it’s attributes (aka columns)

$ rails generate controller will create a skeleton of a controller as well as corresponding views

Newbs can check out the full suite of generators here, but in this post I’ll focus on the mother of all generators, the rails generate scaffold. As you might guess, rails generate scaffold generates a full working MVC with just a couple of keystrokes!

Returning to our book list example, we could get that up and running quite quickly with the following statements in our command line:

$ rails new booksapp #create a new Rails app called booksapp

$ cd booksapp #navigate into your newly created app

$ rails generate scaffold book title author #create a book model with a title attribute and an author attribute. Both attributes will default to string type.

This second instruction of six simple words has Rails generate 19 separate files in your app.  In the next section, we’ll take a look at 4 highly relevant (and instructional) files in the 19.

Newb Note! The below example is based on Rails 4.0.0.  If you want to replicate these steps and unsure how to manage which version of Rails your project will be built with, have of read of my other post Ruby Version Manager (RVM) for Rails Newbs.

Below is a line-by-line explanation of the code appearing in 4 key files created by the rails scaffold command.

db/migrate/20130726235142_create_books.rb:  As the directory and file naming implies (note “db” for database), this file represents instructions for how the  book “model” should be built. The newb will recall from our description above, the model defines the structure of our database.  With this in mind, let’s take a look at this file’s contents.

class CreateBooks < ActiveRecord::Migration
Create a new class called Books, and this class will inherit from ActiveRecord::Migration. As such, some of the following methods are defined by ActiveRecord::Migration.

def change
Create a method called “change”.

create_table :books do |t|
When the change method runs, run a secondary method to create a database table called “books” and then perform the following block of actions. Each distinct action will follow the letter “t”.

t.string :title
In the books table, create a column called “title”.This column will store strings (letters, words).

t.string :author
Create a column called “author”. This column will store strings (letters, words).

Create 2 columns. Each will store date and time formatted information. One column will contain the date and time of day that a new table record is first created. The second column will contain the date and time of day that a table record was last updated.

No further instructions relating to the “create_table” method.

No further instructions relating to the “change” method.

No further instructions relating to the “create a new Class” method.

Remember, this is a migration file. Migrations contain instructions to Rails for how we want our database to change. As outlined above in alarmingly laborious detail, this particular migration instructs Rails to create a table called “Books” and put some stated columns in it.

Next, assuming this all looks good, we tell Rails to execute the migration with a rake db:migrate from the console.

Newb Note!  All table creation migrations will always generate an indexed “ID” column which will contain an incrementing integer of unique value. This is the “primary key” described in the Model earlier.  While this column doesn’t appear in the migration file (or the resulting schema.rb file) Rails will always create it – unless explicitly instructed not to.

With our migration run, let’s look at another file.

app/models/book.rb: As the directory structure and file naming implies, this file represents the book “model”. As we know, the model defines our database architecture and logic. With this in mind, let’s take a look at this file’s contents.

class Book < ActiveRecord::Base
The book class inherits from ActiveRecord::Base.

End of class

This file might seem sparse, but inheriting from ActiveRecord::Base is like being Superman’s child. You get all his special powers and a chance to define your own.

Newb Note! If you’ve run a scaffold under Rails 3, you might have expected to see attr_accessible :title, :author here in support of attribute mass-assignment. While Rails 4 still requires explicit statement of mass-assignable attributes, it does so in the Controller – which we’ll cover a few paragraphs below.

app/views/books/index.html.erb:  As the directory structure and file naming implies, this file represents the book “view” for the index page. The newb will recall from our description above, views serve as a friendly and intuitive way for people to both look at and put information in the database.

<h1>Listing books</h1>
Using “header 1” HMTL styling, put the words “Listing books” on the page.

Let’s create a well formatted table of information in HMTL.

Our table should have a clearly formatted header of column names.

Get ready for a list of those column names.  <tr> is HTML for “table row”. The header with column names is technically just the first row of the table.

Column one should be labeled “Title”.

Column two should be labeled “Author”.

There is a 3rd column, but don’t give it a label.

There is a 4th column, but don’t give it a label.

There is a 5th column, but don’t give it a label.

No more columns.

No more instructions regarding the table header.

Let’s begin to format the table body.

<% @books.each do |book| %>
You’ll note this line looks a little different. The % after the open tag < means some “embedded Ruby” is going to follow. Try to remember this line because it will be important when we move to the Controller. To spill the beans a bit however, @books represents a list of all the books in our database. The list is being passed into the View with this line. .each do instructs Ruby to iterate through each book in the list (in computer science-speak the full list is stored as an “array” of “hashes“) and “do” something with each instance.

For each hash in the array, create a row in our table and put the following in each column:

<td><%= book.title %></td>
In the first column of each row, print the book’s title into the view. Here the newb should note the use of <%= again. As before this means, Ruby will be embedded in the HTML. The difference here from the previous example is the =, which means the Ruby results should be printed in the view (as opposed to just executed without being printed).

<td><%= %></td>
In the second column of each row, print the book’s author into the view.

<td><%= link_to 'Show', book %></td>
In the 3rd column of each row, put the word “Show” on the page as a click-able link for each book. When the link is clicked, look up the book_path helper route for instructions of what to do. In a scaffold scenario, we know this route will redirect the user to localhost:3000/books/[id] where [id] is the primary key of the book in the row where this link has been clicked.

<td><%= link_to 'Edit', edit_book_path(book) %></td>
In the 4th column of each row, put the word “Edit” on the page as a click-able link for each book listed. When the link is clicked, look up the edit_book_path helper route for instructions of what to do. In a scaffold scenario, we know this route will redirect the user to localhost:3000/books/[id]/edit where [id] is the primary key of the book in the row where this link has been clicked.

<td><%= link_to 'Destroy', book, method: :delete, data: { confirm: 'Are you sure?' } %></td>
In the 5th column of each row, put the word “Destroy” on the page as a click-able link. When the link is clicked, present the user with a pop-up prompt asking if they are sure about their desire to delete the specified book from the database. If they answer yes, well – you know what happens.

No more table column/row instructions.

<% end %>
End the.each do embedded Ruby block. Here the newb should take note that the full Ruby block spans multiple lines interspersed with the HTML.

No further table body information.

No further table information.

Put a little vertical spacing on the page.

<%= link_to 'New Book', new_book_path %>
Put the words “New Book” once at the bottom of the page as a click-able link. When clicked, go to localhost:3000/books/new and engage the new method on the books controller.

app/controllers/books_controller.rb:  As the directory structure and file naming implies, this file represents the book “controller”. The newb will recall from our description above, the “controller” acts as the translator and go-between for the model and the view.  With this is mind, let’s look at the file’s contents.

class BooksController < ApplicationController
The books controller inherits from the application controller. Just like inheritance in the Model, our books controller get’s lots of valuable abilities because of who it’s parent is.

before_action :set_book, only: [:show, :edit, :update, :destroy]
This is a Rails “callback“. This particular callback is telling the controller to run a method called “set book” before running the show, edit, update, and destroy methods. The actual logic of the set_book method is defined a little lower down in the file. Hang tight on that.

def index
Let’s define a method called “index”. Now it’s no accident that this method is named exactly like the app/views/books/index.html.erb file we reviewed above. This method is executed every time a user visits the URL localhost:3000/books. Now it’s not actually the word “index” that links the URL and the controller method. The Rails scaffold does that mainly for logical readability. In fact it’s the app/config/routes.rb file that contains the logic of association web pages and controller actions.

@books = Book.all
This short line is doing quite a lot. Hopefully the @books looks familiar. We saw this in the app/views/books/index.html.erb file. There we said that @books represents a list of all the books in our database. @books represents that precisely because of this line. The right hand side of this equation is telling Rails to look in the books model and pass a copy of all the book records into an “instance variable” called @books. This feels like an appropriate place to quickly mention that instance variables in Rails are always preceded with the @ symbol. The power of an instance variable (as opposed to a “local variables” which are generally all lowercase and lack a preceding @) is that instance variables are available to Views. Local variables are only used inside the controller itself. This is a basic, but important, example of variable scoping.

No more instructions for the index method.

The “private” declaration here is another example of scoping. Just above we talked about variable scoping, here we are managing method scoping. Here’s a thorough write-up on method visibility for interested readers.

def set_book
Here we define the set_book method that was referenced in our callback at the top of the file.

@book = Book.find(params[:id])
Just like Book.all returns all the books in the database in the index method, this line extracts a single book record out of the database based on it’s “ID”. Remember that “primary key” value we discussed in the Model section? Here it is being used to go a find a specific book in the database. While params is a powerful piece of Rails that deserves its own blog post, here I’ll just offer the generality that params is the mechanism by which a user can pass information into Rails.

This is the end of the set_book method.

def book_params
Let’s define a method called book_params

params.require(:book).permit(:title, :author)
Along with the working code, the scaffold includes the following comment right into the controller text,

Never trust parameters from the scary internet, only allow the white list through

Basically, this method is the Rails 4 way of handling attribute mass-assignment. Mass-assignment is a security feature in Rails that requires the application developer to explicitly state which columns in the database can be updated en-masse. Without this, a user filling out a form intended to be saved in the database could only submit one piece of information at a time. Image having to fill out your first name and then hit “submit”. After the page refreshes, then you can fill out your last name and then hit “submit”. So on, and so on. You get the idea. Equally important is that we are telling our Model not to accept any user-driven inputs as it relates to the ID field or the timestamp fields discussed previously. These fields are only allowed to be populated by the system itself.

No more instructions for the book_params method.

No more instructions for the books controller!

As a closing note on the controller code above, I intentionally omitted some important methods relating to showing, creating, editing, updating, and deleting records in the database (as well as the associated Views). This was done for brevity, but I hope the detail that has been provided here empowers Rails newbs to more easily interpret those other methods on their own.

So we’ve got a bunch of code here, but let’s see it in action.

$ rails server #start up your local Rails server

Open your favorite browser and go to localhost:3000/books

If you’ve made it this far, you really deserve congratulations and my sincere thanks. As mentioned in the introduction, I remember often only understanding about 20% of the code I was reading. While the tutorials were doing their best to provide the necessary explanation and context to surround the actual code, I felt strongly that a line-by-line explanation of nearly every word would be useful. Now a few months further into my own Rails journey, here it is. I hope it has been of use to you.

I can tell you that writing it mirrored a different kind of emotional dichotomy – this time vacillating between confidence that this blog would serve a purpose and a fear that this work was the equivalent of a dissertation on brushing your teeth. I welcome your feedback on where it fell on that spectrum for you.