37. Rendering Responses

1class ArticlesController < ApplicationController
2  def create
3    @article = Article.new(article_params)
4    
5    if @article.save
6      # Redirect: sends 302, browser makes new request
7      redirect_to @article
8    else
9      # Render: returns response immediately, no new request
10      render :new, status: :unprocessable_entity
11    end
12  end
13end

1class ArticlesController < ApplicationController
2  def show
3    @article = Article.find(params[:id])
4    # Automatically renders app/views/articles/show.html.erb
5  end
6end

1class ArticlesController < ApplicationController
2  def show
3    @article = Article.find(params[:id])
4    
5    # Render same template explicitly
6    render :show
7    
8    # Render different template
9    render :special_show
10    
11    # Render template from another controller
12    render "products/show"
13    
14    # Render with absolute path
15    render file: "/path/to/template"
16  end
17end

1# With status code
2render :new, status: :unprocessable_entity  # 422
3render :error, status: :not_found           # 404
4render :error, status: 500                  # Numeric codes work too
5
6# Without layout
7render :show, layout: false
8
9# With different layout
10render :show, layout: "admin"
11
12# With locals
13render :show, locals: { article: @article, author: @author }
14
15# Set content type
16render :show, content_type: "text/plain"

1def show
2  @article = Article.find(params[:id])
3  
4  # Simple JSON
5  render json: @article
6  
7  # With options
8  render json: @article, only: [:id, :title, :body]
9  
10  # With includes
11  render json: @article, include: :comments
12  
13  # Custom structure
14  render json: {
15    article: @article,
16    meta: { generated_at: Time.current }
17  }
18  
19  # With status
20  render json: { error: "Not found" }, status: :not_found
21end

1def show
2  @article = Article.find(params[:id])
3  
4  # Plain text
5  render plain: "Hello World"
6  
7  # HTML string
8  render html: "<h1>Hello</h1>".html_safe
9  
10  # XML
11  render xml: @article
12  
13  # Raw body
14  render body: "Raw content"
15  
16  # Nothing (empty response)
17  head :ok
18  head :no_content
19  head :created
20end

1class ArticlesController < ApplicationController
2  def index
3    @articles = Article.all
4    
5    respond_to do |format|
6      format.html # renders index.html.erb
7      format.json { render json: @articles }
8      format.xml { render xml: @articles }
9      format.csv { render plain: @articles.to_csv }
10      format.pdf { send_pdf }
11    end
12  end
13  
14  private
15  
16  def send_pdf
17    pdf = ArticlesPdf.new(@articles)
18    send_data pdf.render,
19              filename: "articles.pdf",
20              type: "application/pdf",
21              disposition: "inline"
22  end
23end

1def show
2  @article = Article.find(params[:id])
3  
4  # Render partial as response
5  render partial: "article"
6  
7  # With locals
8  render partial: "article", locals: { article: @article }
9  
10  # Collection
11  render partial: "article", collection: @articles
12  
13  # With layout for partial
14  render partial: "article", layout: "card"
15end

1class ReportsController < ApplicationController
2  include ActionController::Live
3  
4  def download
5    response.headers["Content-Type"] = "text/csv"
6    response.headers["Content-Disposition"] = 'attachment; filename="report.csv"'
7    
8    response.stream.write "id,name,email\n"
9    
10    User.find_each do |user|
11      response.stream.write "#{user.id},#{user.name},#{user.email}\n"
12    end
13  ensure
14    response.stream.close
15  end
16end

1class DownloadsController < ApplicationController
2  def show
3    # Send existing file
4    send_file Rails.root.join("files", "document.pdf"),
5              filename: "document.pdf",
6              type: "application/pdf",
7              disposition: "attachment"  # or "inline"
8    
9    # Send generated data
10    send_data generate_csv,
11              filename: "report.csv",
12              type: "text/csv"
13  end
14  
15  private
16  
17  def generate_csv
18    CSV.generate do |csv|
19      csv << ["ID", "Name", "Email"]
20      User.find_each do |user|
21        csv << [user.id, user.name, user.email]
22      end
23    end
24  end
25end

1class ArticlesController < ApplicationController
2  def create
3    @article = Article.new(article_params)
4    
5    if @article.save
6      # Redirect to show action
7      redirect_to @article
8      
9      # Or explicit path
10      redirect_to article_path(@article)
11      
12      # With flash message
13      redirect_to @article, notice: "Created!"
14      redirect_to @article, alert: "Warning!"
15      
16      # With custom flash
17      redirect_to @article, flash: { success: "Great job!" }
18      
19      # External URL
20      redirect_to "https://example.com"
21      
22      # Back to previous page
23      redirect_back(fallback_location: root_path)
24      
25      # With status
26      redirect_to @article, status: :see_other  # 303
27    end
28  end
29end

1class ArticlesController < ApplicationController
2  def create
3    @article = Article.new(article_params)
4    
5    if @article.save
6      flash[:notice] = "Article created!"
7      redirect_to @article
8    else
9      flash.now[:alert] = "Please fix errors"
10      render :new
11    end
12  end
13  
14  def update
15    # Keep flash for one more request
16    flash.keep(:notice)
17    redirect_to articles_path
18  end
19end

1<!-- In layout -->
2<% flash.each do |type, message| %>
3  <div class="alert alert-<%= type %>">
4    <%= message %>
5  </div>
6<% end %>

1class ArticlesController < ApplicationController
2  def check
3    if Article.exists?(params[:id])
4      head :ok
5    else
6      head :not_found
7    end
8  end
9  
10  def destroy
11    Article.find(params[:id]).destroy
12    head :no_content  # 204
13  end
14end