2 Learn Ruby on Rails: Book Two Version , 1 March Daniel Kehoe ii Contents 1 Free Offer 1 2 Introduction 3 Is It for You?. Ruby on Rails is an extremely productive web application framework All the content and graphics published in this e-book are the property of. Download Ruby Tutorial Ruby on Rails 3 Tutorial Learn Rails by portal7.info Book 1 subject: C Programming Tutorial Book 1 book_id: Book 2.
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Getting started with Ruby on Rails, Routing, ActiveRecord, Views, Angular with Rails; Rails logger; Prawn PDF; Rails API; Deploying a Rails app on Heroku. Newly updated for Rails 5, the Ruby on Rails Tutorial book and screencast series and is available for download as an ebook (PDF, EPUB, and MOBI formats). Get a free 8-part email course & priority notifications about the Ruby on Rails. Newly updated for Rails 5, the Ruby on Rails Tutorial book and screencast series and is available for download as an ebook (PDF, EPUB, and MOBI formats).
Newly updated for Rails 5, the Ruby on Rails Tutorial book and screencast series teach you how to develop and deploy real, industrial-strength web applications with Ruby on Rails, the open-source web framework that powers top websites such as Twitter, Hulu, GitHub, and the Yellow Pages. The companion screencast series includes 14 individual lessons, one for each chapter of the Ruby on Rails Tutorial book. This book by Michael Hartl came so highly recommended that I had to try it, and the Ruby on Rails Tutorial is what I used to switch back to Rails again. This is also the only Rails book that does test-driven development the entire time, an approach highly recommended by the experts but which has never been so clearly demonstrated before. The linear narrative is such a great format.
Understanding Version Numbers Rails follows a convention named semantic versioning: For example, switching from Rails 3. For ex- ample, Rails 3. Ruby and Rails Version Check Check that appropriate versions of Ruby and Rails are installed in your devel- opment environment. Rails 4. See the Installing Rails instructions for your computer. Versions such as 5. You can check for the current version of Rails here. Rails 5.
If you have Rails 5. If the Rails 5 version of this book is not yet available, you must install Rails 4. RVM I promised that this book would introduce you to the practices of professional Rails developers. RVM lets you switch between different versions of Ruby. RVM also helps you manage your collections of gems, by letting you create multiple gemsets. When a new version of Rails is released, you can create a new gemset with the new Rails version when you start a new project.
Your old project will still have the version of Rails it needs in its own gemset. RVM will show you a list of available Ruby versions: You will see a global gemset as well as any others you have created, such as a gemset for Rails4.
RVM is not the only utility you can use to manage multiple Ruby versions. Some developers like Chruby, rbenv, or others. Enter these commands: Linux users may need to check instructions for Integrating RVM. Open a terminal and type: Starter Applications Rails provides a framework; that is, a software library that provides utilities, conventions, and organizing principles to allow us to build complex web ap- plications.
Rails gives us the basics we need for many websites. We also might want to add gems that enhance Rails to aid development gems for testing, for example or improve the look and feel of our application the Bootstrap or Foundation front-end frameworks. Developers often mix and match components to make a customized Rails stack.
Most experienced developers have one or more starter applications that save time when beginning a new project.
The RailsApps project was launched to provide open source starter applications so developers could collaborate on their starter applications and avoid duplicated effort.
After you gain some skill with this tutorial, you might use the RailsApps starter apps to instantly generate a Rails application with features like authentication, authorization, and an attractive design.
For help, see Install Ruby on Rails - Ubuntu. Viewing in the Web Browser To see your application in action, open a web browser window and navigate to http: Box 6.
Viewing on a Hosted Platform It is easy to see your web application in action on your local computer. If you are using a hosted service such as Cloud9 or Nitrous. You can also open a browser tab or window and enter the URL for the application, as hosted by Cloud9.
When you launch the Rails server, Cloud9 displays a helpful message showing the URL where you can view your application. If you are using Nitrous. These diagnostic messages are an important tool for troubleshooting when you are developing. Multiple Terminal Windows You can keep more than one terminal window open. For convenience, you may want to keep a terminal window open for running the web server and watch- ing diagnostic messages.
To some people, the text editor and the terminal window look very similar. The terminal window is very different. Your computer can run multiple programs at once. You can open multiple terminal windows. In each terminal window, you can use the command line to launch a different program. Each program you start in a terminal window is a separate process and multiple processes can run simultaneously. You can end a process by pressing Control- c in most cases , Control-d in some cases , or closing the terminal window almost always.
From this perspective, a terminal window is a tool you use to launch processes and your computer is a machine that runs processes. Changes will automatically appear when you refresh the browser or request a new page. There is a tricky exception, however. Get Organized for Efficiency Before we learn about the Rails directory structure, take a minute to organize your screen real estate.
Open a window in the terminal application, place it on the left side of your screen, and stretch it to the maximum vertical height of your screen. Open multiple tabs in your terminal application.
Keep one tabbed window open for entering shell commands like cd or ls and another terminal window open for running the rails server command and viewing the log output. Place your text editor window next to the terminal window and stretch it to full vertical height. If you are using Atom or Sublime Text, you can open two editor panels side-by-side. If you have enough screen space, leave your web browser open and place it next to your text editor.
If your screen space is limited, you may have to overlap the web browser with the text editor, but position your web browser window so you can bring it to the front with a single click. Open tabs for http: The rails new command has created a project directory for us.
It is a parking structure for our code. Unlike an ordinary parking structure, where you park anywhere you like, this garage has assigned parking. You have to park your code in the right place. This is Rails, where convention brings order to the development process. Rails is a software machine with many mov- ing parts; the project directory provides a structure to manage the complexity. The logic and order of the project directory structure is familiar to every Rails developer, and consistent for every Rails application, which makes it easy to collaborate, maintain an application, and create open source projects.
Gemfile Gemfile. Rails directory structure. Get to Know the Folders and Files To get you started, here are three tables. The third table is a preview of things to come. This is where you will spend your time in Rails. Rails app folder. You can also use your text editor to view the folder.
Or do it with Unix commands: This makes it easy to collaborate with other Rails developers, providing consistency and predictability. The mailers folder is for code that sends email messages. Rails provides a basic model—view—controller framework but it is often necessary to extend it. Use the cd.. This chapter will introduce you to software source control, also called version control or revision control. But it makes professional software development possible and, at the core, it is essentially a form of time travel.
To understand time travel, we need to understand state. We know about states of matter. Water can be ice, liquid, or steam. Imagine a machine with a button that, each time it is pressed, changes water from one state to another.
We call this a state ma- chine. Almost every software program is a state machine. When a program receives an input, it transitions from one state to another. Light or dark. Ice, liquid, or steam. Or, in a web application: We look things up, we think, we type errors and we make corrections. We want to preserve the state of our work. More importantly, it archives a snapshot of the current state in a repository where it can be retrieved if needed. We can go back and recover the state of our work at any point where we committed a snapshot to the repository.
In software development, travel to the past is essential because we often make mistakes or false starts and have to return to a point where we know things were working correctly.
What about time travel to the future? Version control systems allow us to explore alternative futures by creating a branch for our work. Git The dominant version control system among Rails developers is Git, created by the developer of the Linux operating system. Unlike earlier version control systems, Git is ideal for wide-scale distributed open source software development.
Well-written com- mit messages describe your work to co-workers or open source collaborators. That means you can customize an open source project for your own needs. Fixing bugs large or small and adding features to open source projects are how you build your reputation in the Rails community. Collaboration is easy when you use a branch in Git.
If you and a coworker are working on the same codebase, you can each make a branch before adding to the code or making changes. Git supports several kinds of merges, so you can integrate your branch with the trunk when your task is complete. All the power of Git comes at a price. Have you noticed how time travel movies require mental gymnastics, especially when you try to make sense of alternative futures and intersecting timelines?
You can build the tutorial project without using Git. But I urge you to use Git and a GitHub account for this project, for two reasons. Before I show you Git commands, I want to mention that some people use graphical client applications to manage Git. It will take effort to master Git; the commands are not intuitive. But it is absolutely necessary to become familiar with Git basics.
Is Git Installed? If Git is not found, install Git. See the article Rails with Git and GitHub for installation instructions. Is Git Configured? Make sure Git knows who you are. Every time you update your Git repository with the git commit command, Git will identify you as the author of the changes.
Use the same email address for Git, your GitHub account, and Heroku to avoid headaches. Extending the time traveler analogy, initializing a Git repository is equivalent to setting up the time machine. We add the Unix symbol that indicates Git should be initialized in the current directory git init dot: Initialized empty Git repository in It creates a hidden folder named.
You can peek at the contents: GitIgnore The hidden. The rails new command creates a. Take a look at the contents of the. If you find yourself ignoring temporary files generated by your text editor or operating system, you probably want to add a global ignore instead: But the story of your project would be confusing and overly detailed. Do so now: There are three forms of the git add command: Like time travel, Git will stretch your understanding of what makes sense.
Most often, you can simply use the git add -A form of the command. Now commit your project to the repository: The pristine state of your new Rails application is now recorded in the repo. Fri Dec 18 I like to use the git log command with an option for a compact listing: The commit ID is abbreviated but it is all you need to travel back in time.
A fourth stage is important when you work with others: The repositories hosted on your GitHub account establish your reputation as a Rails developer for employers and developers you may work with. Did you create a GitHub account? Now would be a good time to add your repo to GitHub. Go to GitHub and create a new empty repository for your project.
If the repository is public, hosting on GitHub is free. Add GitHub as a remote repository for your project and push your local project to GitHub. Before you copy and paste the command, notice that you need to in- sert your own GitHub account name.
Now you can view your project repository on GitHub at: Take a look. GitHub is abso- lutely essential to all open source Rails development. It will be good practice for using Git. Markdown is a popular way to add formatting to improve readability. Very cool! The git log command will display your project history: Chapter 9 Gems The art of selecting gems is at the heart of Rails development.
Some gems add functionality or features to a website. Other gems play a supporting role, making development easier or implementing basic infrastructure.
Gems are open source. Gems are often created when a developer has used the same code as a component in more than one web application.
He or she will take time to release the code as a gem. There is no evaluation or review process in publishing gems. Gems are hosted on a public server, rubygems. A single command, gem push, uploads a gem to the rubygems. Over 50, gems have been released since rubygems. Some of these gems are used by one or two developers on their own projects. GEMS Many others have been neglected and abandoned due to lack of interest.
Only a few thousand gems are popular and widely used. There is no single authoritative source of recommendations for gems. The Ruby Toolbox website categorizes and ranks many gems by popularity, and it is a good place to begin hunting for useful gems. How many are closed? Popular gems are likely to have many reported issues, some of which are trivial problems or feature requests.
Gems that are actively maintained will have many closed issues and, ideally, only a few open issues. Regular and recent activity in the commit log indicates the gem is actively maintained.
Rails Gems Rails itself is a gem that, in turn, requires a collection of other gems.
This becomes clear if you look at the summary page for Rails on the rubygems. Each of these gems has its own dependencies as well. When you install Rails, a total of 44 gems are automatically installed in your development environment. Gems for a Rails Default Application In addition to the Rails gem and its dependencies, a handful of other gems are included in every rails new default starter application: Where Do Gems Live?
Gems are handled by the Ruby interpreter no differently than your own code. Experienced programmers who have used software libraries in other languages might wonder how it works.
Ruby has a require method that allows you to import software libraries into your programs. You can run the gem env command to reveal the RubyGems environment details which are normally hidden from you: If you use RVM, gems are saved to a hidden. A global subfolder contains the Bundler gem. It lists each gem that the developer wants to use. Bundler checks to see if the gem is already installed and only downloads gems that are needed. Bundler checks for the newest gem version and records the version number in the Gem- file.
Bundler also downloads any gem dependencies and records the dependencies in the Gemfile. More importantly, when other devel- opers install your application, Bundler will automatically install all the gems including dependencies and correct versions needed to run the application. When you deploy the application to production for others to use, automated deployment scripts such as those used by Heroku install all the required gems.
Bundler provides a bundle update command when we want to replace any gems with newer versions. If you run bundle update, any new gem ver- sions will be downloaded and installed and the Gemfile. Be aware that updating gems can break your application, so only update gems when you have time to test and resolve any issues. You can run bundle outdated to see which gems are available in newer versions.
The exception is the Rails gem itself. We always specify the version of Rails we are using for de- velopment. GEMS gem 'jquery-rails' Turbolinks makes following links in your web application faster Read more: Some version numbers may be different if a newer Rails version was released since this was written. Rails changes frequently and newer versions may not work as we expect.
This is needed for au- tomated deployment scripts such as those used by Heroku. Other gems are commented out the lines begin with the character. These are suggestions and we can ignore them or remove them. If you remove the extra clutter in the Gemfile it will look like this: I learned of these gems from a variety of different sources: We want to stick with the Foundation 5 framework, not the newer Foundation 6 framework, to avoid some potential errors.
Rails let you specify groups for development, test, or production. What version of Rails is installed in your current gemset? Check with: Change this line as needed: Install the required gems on your computer: Fetching gem metadata from https: Resolving dependencies Using rake Your bundle is complete! You can use your text editor to view the contents of Gemfile. Run gem list to see all the gems that are loaded into the development envi- ronment: If your devel- opment environment is not set up correctly, you may see error messages when Bundler attempts to install the Nokogiri gem.
Nokogiri is often needed by other gems it is a dependency of some gems and Nokogiri can become a problem to install. Unlike most gems that are written in pure Ruby, parts of Nokogiri are written in the C language and must be compiled using system tools that vary with different operating systems.
If you get a message: GIT 85 fatal: Not a git repository or any of the parent directories: You are probably not in your project directory. Use the Unix command pwd to see where you are. To investigate, enter: Configuration Security GitHub is a good place to store and share code. But when your repos are public, they are not a good place for secret account credentials. Operating systems Linux, Mac OS X, Windows provide mechanisms to set local environment variables, as does Heroku and other deployment platforms.
With a bit of Unix savvy, you can set environment variables using the Unix shell. The article Rails Environment Variables shows alternatives to using Unix en- vironment variables, if for any reason you cannot set environment variables on your machine. The shell is the program that gives us the command line interface we see in the Terminal or console application.
Unix gives you a choice of shell programs with names like sh, bash, ksh, and zsh ; each has a slightly different way to set environment variables. The most common shell program is bash. You should see either. The command might not be exactly the same but it is likely you will see some export com- mands.
Set Environment Variables Set the following environment variables in your. You can use Command-Shift-. The credentials are the same you use to sign in to the SendGrid website.
Add your SendGrid username and password to your. Have you already created a MailChimp mailing list? Troubleshooting Check that the SendGrid user name is set in your Unix environment variables: Close and reopen your terminal to make sure the environment includes any recent changes. Most computers use the bash shell and you can set environment variables in your. But not every system is alike.
Be sure to restart your server when you modify this file. Your secret key is used for verifying the integrity of signed cookies. If you change this key, all old signed cookies will become invalid! Make sure the secret is at least 30 characters and all random, no regular words or you'll be exposed to dictionary attacks.
Make sure the secrets in this file are kept private if you're sharing your code publicly. For development, use example. If you have your own domain name, you can use that instead. Be sure to use spaces, not tabs. Make sure there is a space after each colon and before the value for each entry. Replace the following: If your password contains any of these characters you should sur- round the string with single quotes: Go to your Rails application directory and create a new secret token: You can learn more in the article Send Email with Rails.
In the early days of the Internet, an experienced system administrator could set up an SMTP server to distribute email. Now, because of efforts to reduce spam, it is necessary to use an established email service to ensure deliverability. In production, for high volume transactional email and improved deliverability, it is best to use a service such as SendGrid.
Alternatives are: For convenience during development, some developers use their own Gmail account to send email. After the code you just added, add the statement: Send email in development mode? Later, after we add a contact form to the tutorial application, the application will be ready to send email messages. The pages are delivered fast and no Ruby code is required.
Add a Home Page Make sure you are in your project directory. Start the application server: The Rails application server looks for any pages in the public folder by default. Since then, index. Enter the URL http: If you are using Cloud9 or Nitrous. Introducing TDD With test-driven development, a developer tests behavior before implementing a feature, expecting to see an error condition. Then the developer implements the feature and sees a successful result to the test.
Beginners tend to think TDD is scary and complicated. Real TDD means writing tests in Ruby before implementing features, but the principle is the same. But what if you want to override the default behavior? Here is where it is helpful to have two terminal sessions going in different tabs. There is no need to restart your application server to see the new behavior. If you need to start the server: The code is buried deep in the Rails framework.
However, if you know the convention and the technique for overriding it, you have both convenience and power at your disposal. Web browsers make requests. The beauty and simplicity of the World Wide Web architecture, as conceived by Tim Berners-Lee in , is that the web is nothing more than a request from a web browser and a response from a web server.
We can reduce the mystery of how the web works to its simplest components when we investigate the request-response cycle. Figure The request-response cycle. Inside the Browser We can see the actual request, and the actual response, by using the diagnostic tools built into the web browser. Start the application server if it is not already running: Even if you prefer Mozilla Fire- fox or Apple Safari, try this in Chrome, so you can follow along with the text.
Alternatively, you can clear the browser cache. Select the Network tab in the Developer Tools View. There is only one: The request is composed of: Viewing a request in the Developer Tools View. Now try requesting the home page by entering the URL http: For that, go to the server logs or the console window.
Notice how the diagnostic messages in the console window match the headers in the browser diagnostic view. Notice there are no console log messages for pages delivered from the public folder.
Document Object Model What happens after the browser receives a response from the server?
It provides a structural representation of the document. Here is a diagram that shows what happens in the server during the request- response cycle. You learned earlier that, from the perspective of a software architect, Rails is organized to conform to the model—view—controller software design pattern. The MVC design pattern is optimal for web applications and is a central organizing principle for Rails. The MVC design pattern originated in the design of desktop applications.
We can see the reason for the quibble in the next diagram. The diagram shows the MVC architecture as part of the Rails software stack.
At the base of the stack is the web browser. Despite the quibble about nomenclature, the architecture is well understood and used by all Rails developers. The controller will obtain any needed data from a model. After obtaining data, the controller will render a response combining data from the model with a view component that provides markup and layout.
The model, view, and controller classes you create will inherit behavior from parent classes that are part of the framework, so you will have less code to write yourself. In most Rails applications, a model obtains data from a database, though some models obtain data from a remote connection to another server. For example, a User model might retrieve a user name and email address from a local database.
The controller can obtain data from more than one model if necessary. A controller can have more than one action. For example, a User controller might have actions to display a list of users, or add or delete a user from a list.
We use the terms action and method interchangeably when we talk about a Rails controller; to be precise, controller actions are implemented as methods. An index view might show a list of users. In many controllers, on com- pletion, the destroy action will redirect to the index view, and create will redirect to either show or new. This conceptual overview will be easier to grasp when you actually see the code for a model, view, and controller. You can leave it in place.
Viewing request headers in the Developer Tools View. Model—View—Controller in Rails. Model—View—Controller stack in Rails. Our goal is to build a practical web application that you can really use. We can create the routes, model, view, and controller in any order. All must exist before our web application will respond to a request for a home page. The Name Game Much of the art of programming lies in choosing suitable names for our cre- ations.
In Rails, there is often a model with the same name as a controller though a controller can use data from multiple models. Replace the contents with this: It will be become familiar soon and you can look up the details in the reference documentation, RailsGuides: Routing from the Outside In. Model Most Rails models obtain data from a database. When you use a database, you can use the rails generate model command to create a model that inherits from the ActiveRecord class and knows how to connect to a database.
This simple class provides an easy introduction to Ruby code. Software architects call these abstrac- tions objects. In Ruby, everything we create and manipulate is an object. Ruby makes it easy for a method to return data when called; the value assigned by the last statement will be delivered when the method is called.
The variable is named on the left side of the equals sign; a value is assigned on the right side. We call the equals sign an assignment operator. Not surpris- ingly, a number also can be assigned to a variable, either a whole number an integer or a decimal fraction a float. More interestingly, any Ruby object can be assigned to a variable.
We can create our own objects, as we have by creating the Owner class. Or we can use the library of objects that are supplied with Ruby. The Rails API gives us additional classes that are useful for web applications.
Learning the syntax of Ruby code gets you started with Ruby programming; knowing the API classes leads to mastery of Ruby. It is described in the Ruby API reference documentation.
The Date class has a Date. You can see this syntax when we assign Date. The Date. Imagine a September birthday. You must use Date. If you enter a date in the format Date. When the Date. The Date class can perform complex calendar arithmetic. The variables birthdate and today are instances of the Date class.
The if Then we subtract today from birthday. This shows you the power of programming in Ruby. Notice that I needed 16 paragraphs and over words to explain 15 short lines of code. But without knowing more than this, we can build a simple web application. View The Owner model provides the data we want to see on the Home page. In a typical application, one controller can render multiple views, so we make a folder to match each controller. Or use the Unix mkdir command: Some experi- enced developers prefer to add gems that provide the Haml or Slim templating engines.
As you might guess, a View that uses the Haml templating syntax would be named new. This markup allows us to insert Ruby code which will be replaced by the result of evaluating the code.
You may have noticed that we refer to the Owner model with the variable owner. It will be clear when we create the Visitors controller why we use this syntax a variable name that begins with the character is called an in- stance variable. The Rails implementation becomes useful if the name is retrieved from a database or created programmatically.
There is no way to display a calculation using only static HTML, so Rails gives us a way to display the birthday countdown calculation. Controller The Visitors controller is the glue that binds the Owner model with the Visi- torsController new view. In this context, the character is only a documentation con- vention. The class name is written in camelCase with a hump in the middle, like a camel so we can combine two words without a space.
We create an instance variable named owner and assign an instance of the Owner model. Keep in mind the purpose of the controller. Each controller action method responds to a request by obtaining a model if data is needed and rendering a view. The new method is deceptively simple. Hidden behavior inherited from the ApplicationController does all the work of rendering the view. We can make the hidden code explicit if we wish to. It would look something like this: Rails often offers default behavior that looks like magic because the underlying implementation is hidden in the depths of the Rails code library.
Revealing the hidden code, we see that invoking the new method calls a render method supplied by the ApplicationController parent class. The code underlying the render method is complex. Rails takes care of the rest. As you gain experience, you can dive into the Rails source code to unravel the magic. Scaffolding This tutorial aims to give you a solid foundation in basic concepts. The model— view—controller pattern is one of the most important.
For example, Rails Guides: Students often use scaffolding to create simple Rails applications. Enter the command: Dynamic home page shows days until a birthday.
And the underlying code conforms to the conventions and structure of Rails. Git At this point, you might have the Rails server running in your console window.
You might think you have to enter Control-c to shut down the server and get the command prompt. You can open more than one console window. Your terminal application lets you open multiple tabs so you can easily switch between windows without using a lot of screen real estate.
It is convenient to have a console window open for the server and another for various Unix commands. Before we do any more work on our tutorial application, we need to learn about troubleshooting and debugging. Use the git status command to check: Interactive Ruby Shell There will be times when you want to try a snippet of Ruby code just to see if it works.
IRB is a Ruby interpreter that runs from the command line. It executes any Ruby code and provides an immediate response, allowing you to experiment in real-time. If you enter a valid Ruby expres- sion, the interpreter will display the result of evaluating the expression.
Try simple arithmetic: You are using your computer for simple math. Maybe you can delete the calculator app from your phone. IRB will evaluate any Ruby expression and helps you quickly determine if syntax and logic is correct.
Actually, IRB can handle multiple lines of code. Try it: Pry is a powerful alternative to the standard IRB shell for Ruby. As you gain experience, you might take a look at Pry to see what the enthusiasm is all about. Your application will be running as if the application was waiting to respond to a web request. Then you can expose behavior of any pieces of the web application.
Loading development environment Rails 4. The prompt shows it is ready to evaluate an expression. Then we can use the Owner. Each instance is a unique object with its own data attributes but the same behavior as other objects in- stantiated from its class.
The bits that were organized to create the variable name will evaporate into the ether. Enter Control-d or type exit to quit the Rails console. The Rails console is a useful utility. It is like a handy calculator for your code. Use it when you need to experiment or try out short code snippets. Rails Logger As you know, a Rails application sends output to the browser that makes a web request. On every request, it also sends diagnostic output to the server log file.
Scrolling the console win- dow is a good way to see diagnostics for every request. You can add your own messages to the log output by using the Rails logger. You could see how the application behaves, step by step.
The Rails logger is the best tool for the job. In a controller, you can use the method logger on its own. In a model, you have to write Rails. You can use any of the methods logger. Log messages written with the logger. If you want your log messages to stand out, you can add formating code for color: Debugging Rails Appli- cations. Revisiting the Request-Response Cycle Earlier, when we investigated the request-response cycle, we looked in the server log to see the response to the web browser request.
We can see evidence of the model-view-controller architecture. Our debug statements show we enter the new method and reveal the value of the Owner name. As we learned, the model-view-controller architecture is an abstract design pat- tern. Now we can see it as activity in the server log. Error page. In the console log, the stack trace will show everything that happens before Rails encounters the error: There are times when it pays to carefully read through the stack trace line by line, but most often, only the top line of the stack trace is important.
The point of this exercise is to encourage you to read the top line of the stack trace and use it to diagnose the problem.
However, there is a better way to force your program to halt, called raising an exception. Rails includes various exception handlers to display errors in production so users will see a helpful web page explaining the error. Check the status to make sure: By all means, if you love the precision and order of programming languages, dive into the study of Ruby from the beginning. Reading Knowledge of Ruby What you need, more than anything, when you start working with Rails, is reading knowledge of Ruby.
It will not be a model, view, controller, or any other standard component of Rails. The jaws that bite, the claws that catch! Beware the Jubjub bird, and shun The frumious Bandersnatch! But it is unclear how the author intends anyone to use the code. In this case, I just want to give you some code that illustrates typical Ruby syntax and structure. Code is only strings of characters. But some strings have special meaning for everyone and all others are arbitrary words that only have meaning to an individual developer.
Some made-up words will be obvious because they are just too idiosyncratic to be part of the Ruby language. There is only one way to be sure which words are part of the Ruby language: Check the Ruby API. You can use IRB to try out the example code in the console. The ex. Remember you can use Control-d to exit from IRB. Whitespace and Line Endings Whitespace characters such as spaces and tabs are generally ignored in Ruby code, except when they are included in strings.
Some programming languages Java and the C family require a semicolon as a terminator character at the end of statements.
Ruby does not require a semicolon to terminate a statement. Comments Ruby ignores everything that is marked as a comment. Use comments for notes to yourself or other programmers. This is a comment. Code must exactly follow the syntax of a lan- guage. Typos, guesses, and code that is almost-but-not-quite right will simply fail, often without any helpful error messages. Computers seem intelligent because they can execute code conditionally. You can write a program so that given one set of conditions, certain parts of the code will execute, and given different conditions, other parts of the code will execute.
Lastly, programs are written to transform abstractions from one form to another. When we learn simple arith- metic, we learn we can take the symbols for numbers and add them together to make a different number. Computer programs do more than add numbers; a program can transform words and other abstractions.
Assignment In Ruby, like many other programming languages, the equals sign indicates we are assigning a value. The equals sign is the assignment operator. And name is a variable that stores the value so it can be easily reused.
Just as we can assign a value to a variable, we can reassign a new value when- ever we want. That is why we call them variables; the value can vary. Foobar Kadigan' Variables can be assigned strings of letters, numbers, or anything else. Object-Oriented Terminology Software architects use a common vocabulary to talk about programming lan- guages: You can write code and intuitively grasp the meanings. Or you can gain an understanding by applying metaphors. Houses For example, some programming textbooks attempt to explain a class like this: A blueprint for a house design is like a class definition.
Created with Sketch. Sign In Sign Up. About the Book For a solid start on Ruby on Rails web development You've got experience with the web and need to learn Rails You don't know how to program -- but want to learn You want to build an application You want to start a career as a professional web developer You can find this book on site , with dozens of 5 star reviews, in a Kindle edition. Share this book Feedback Email the Author s. Introduction Is It for You?
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