All source code included in the card Rails always tries to use a layout with the same name as your controller is licensed under the license stated below. This includes both code snippets embedded in the card text and code that is included as a file attachment. Excepted from this license are code snippets that are explicitely marked as citations from another source.
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Growing Rails Applications in Practice. Learn to structure large Ruby on Rails codebases with the tools you already know and love. The model-view-controller MVC architecture that we first encountered in Chapter 1 is not unique to Rails. In fact, it predates both Rails and the Ruby language by many years. Rails, however, really takes the idea of separating an application's data, user interface, and control logic to a whole new level.
Let's take a look at the concepts behind building an application using the MVC architecture. Once we have the theory in place, we'll see how it translates to our Rails code. MVC is a pattern for the architecture of a software application. It separates an application into the following components:. Separating a software application into these three distinct components is a good idea for a number of reasons, including:. If you're struggling to get your head around the concept of MVC, don't worry.
For now, what's important to remember is that your Rails application is separated into three distinct components. Jump back to the MVC diagram if you need to refer to it later on. Rails promotes the concept that models, views, and controllers should be kept separate by storing the code for each element as separate files in separate directories.
Rails always tries to use a layout with the same name as your controller
This is where the Rails directory structure that we created back in Chapter 2 comes into play. It's time to poke around a bit within that structure. If you take a look inside the app directory, depicted in Figure , you'll see some folders whose names might start to sound familiar. As you can see, each component of the model-view-controller architecture has its place within the app subdirectory—the models , views , and controllers subdirectories respectively. We'll talk about assets in Chapter 7, helpers in Chapter 6, and mailers later on in this chapter.
This separation continues within the code that comprises the framework itself. The classes that form the core functionality of Rails reside within the following modules:. ActiveRecord is designed to handle all of an application's tasks that relate to the database, including:. ActiveRecord has a few other neat tricks up its sleeve. Let's look at some of them now. The ActiveRecord module is based on the concept of database abstraction. As a refresher from Chapter 1, database abstraction is a way of coding an application so that it isn't dependent upon any one database.
Code that's specific to a particular database server is hidden safely in ActiveRecord , and invoked as needed. The result is that a Rails application is not bound to any specific database server software. Should you need to change the underlying database server at a later time, no changes to your application code are required. There are those that disagree with the approach taken by ActiveRecord , so you'll hear a lot about that, too. For now, I suggest you learn the way ActiveRecord works, then form your judgement of the implementation as you learn. Some examples of code that differ greatly between vendors, and which ActiveRecord abstracts, include:.
Before I can show you the magic of ActiveRecord in action, though, a little housekeeping is necessary. Tables are the containers within a relational database that store our data in a structured manner, and they're made up of rows and columns. The rows map to individual objects, and the columns map to the attributes of those objects.
The collection of all the tables in a database, and the relationships between those tables, is called the database schema. An example of a table is shown in Figure In Rails, the naming of Ruby classes and database tables follows an intuitive pattern: What's nice about the mapping between classes and tables is that there's no need to write code to achieve it; the mapping just happens, because ActiveRecord infers the name of the table from the name of the class.
Note that the name of our class in Ruby is a singular noun Story , but the name of the table is plural stories. This relationship makes sense if you think about it: But the SQL table holds a multitude of stories, so its name should be plural. While you can override these conventions—as is sometimes necessary when dealing with legacy databases—it's much easier to adhere to them. The close relationship between objects and tables extends even further. If our stories table were to have a link column, as our example in Figure does, the data in this column would automatically be mapped to the link attribute in a Story object.
And adding a new column to a table would cause an attribute of the same name to become available in all of that table's corresponding objects. Instead, I encourage you to download the following script from the code archive, and copy and paste it straight into your SQLite console that you invoked via the following command in the application directory:.
Once your SQLite console is up, paste in the following: You don't have to worry about remembering these SQL commands to use in your own projects; instead, take heart in knowing that in Chapter 5 we'll look at migrations. Migrations are special Ruby classes that we can write to create database tables for our application without using any SQL at all.
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Even though Rails abstracts away the SQL required to create tables and database objects, you'd be doing yourself a favor if you become familiar with SQL and its syntax. SitePoint has published a book on learning SQL, so check that one out. Now that we have our stories table in place, let's exit the SQLite console simply type. A Rails console is just like the interactive Ruby console irb that we used in Chapter 2, but with one key difference.
In a Rails console, you have access to all the environment variables and classes that are available to your application while it's running.
These are not available from within a standard irb console. To enter a Rails console, change to your readit folder, and enter the command rails console or rails c , as shown in the code that follows. To start using ActiveRecord , simply define a class that inherits from the ActiveRecord:: We touched on the:: It can also be used to refer to classes that exist within a module, which is what we're doing here.
Flip back to the section on object-oriented programming OOP inChapter 3 if you need a refresher on inheritance. These two lines of code define a seemingly empty class called Story ; however, this class is far from empty, as we'll soon see.
4. Managing Data Flow: Controllers and Models - Learning Rails 3 [Book]
From the Rails console, let's create this Story class and an instance of the class called story by entering these commands:. As you can see, the syntax for creating a new ActiveRecord object is identical to the syntax we used to create other Ruby objects in Chapter 3. At this point, we've created a new Story object; however, this object exists in memory only—we're yet to store it in our database. Since the object is yet to be saved, it will be lost when we exit the Rails console. To save it to the database, we invoke the object's save method:. Now that we've saved our object a return value of true indicates that the save method was successful , our story is no longer a new record.