The value of DRY code.

The concept of Do Not Repeat Yourself or DRY in coding is a concept most programmers learn from the beginning. Similar to a real life conversation, you wouldn’t like very much if whomever you were conversing with kept saying the same thing over and over again; likewise if you yourself had to keep bringing up the same point.

This concept translates very well to coding. The idea of stating something only once and have it carry through the entire ‘conversation’ between you and the application. As a programmer you don’t want to have to code the same thing twice. Below is a simple example of how to implement certain methods to enforce DRY coding.

Here is an example from a simple Rails blogging application, here is what the Articles Controller initially looked like:

class ArticlesController < ApplicationController    
def index        
 @articles = Article.all    
end
    
def show        
 @article = Article.find(params[:id])    
end
  
def new        
 @article = Article.new    
end 
def edit        
 @article = Article.find(params[:id])    
end
  
def create        
 @article = Article.new(params.require(:article).permit(:title,    :description))        
 if @article.save            
 flash[:notice] = "Article was created successfully!"                redirect_to @article        
else            
render 'new'        
end    
end
def update
 @article = Article.find(params[:id])        
 if @article.update(params.require(:article).permit(:title,  :description))
 flash[:notice] = "Article was updated successfully!"            redirect_to @article
else            
render 'edit'        
end    
end
def destroy        
 @article = Article.find(params[:id])        
 @article.destroy         
 redirect_to articles_path    
end
end

There is a lot to unpack here, but this code is pretty clunky. With all the repetition, it increases the chance of an error. Notice how the line

@article = Article.find(params[:id]) occurs 4 times throughout the controller and yes I actually coded this 4 times over just to prove this point.

Notice that also in the create and update methods we have the line

(params.require(:article).permit(:title, :description))

we can fix this as well by introducing two methods to clean up this code.

Let’s take of the first problem, we’ll create some private methods for this controller, the first one will be called ‘set_article’.

def set_article        
 @article = Article.find(params[:id])    
end

Now we need to make sure that ‘set_article’ gets used for those 4 methods.

At the top of the controller we add:

class ArticlesController < ApplicationController    
before_action :set_article, only: [:show, :edit, :update, :destroy]

This means that before anything happens, those methods will implement the ‘set_article’ method, no longer having to code it over and over again!

Now for the ‘params.require …’ line that’s just ensuring that the articles have all the require attributes when they are being created, they must have a title and description. It can be cleaned up using another private method. This one will be called ‘article_params’

def article_params        
 params.require(:article).permit(:title, :description)    
end

Now in the create and update methods, simply just pass in ‘article_params’ as the argument.

The shiny, new, DRY Articles Controller looks like this:

class ArticlesController < ApplicationController
    before_action :set_article, only: [:show, :edit, :update, :destroy]
def index
 @articles = Article.all
end
def show
end
def new
 @article = Article.new
end
def edit
end
def create
  @article = Article.new(article_params)
    if @article.save
      flash[:notice] = "Article was created successfully!"
      redirect_to @article
    else
      render 'new'
   end
end
def update
  if @article.update(article_params)
     flash[:notice] = "Article was updated successfully!"
     redirect_to @article
  else
     render 'edit'
  end
end
def destroy
  @article.destroy
  redirect_to articles_path
end
private
def set_article
   @article = Article.find(params[:id])
end
def article_params
   params.require(:article).permit(:title, :description)
  end
end

Much better!