How to Add a Custom ERB Template to Rails Scaffold Generator

Brief Answer

To add a custom ERB template to your Rails scaffold generator, you need to place the template in the correct directory structure and ensure your generator method properly references it. The key issue in your implementation is the incorrect path specification in the template method call. Your template should go in app/lib/generators/templates/erb/scaffold/ and the method should reference it with the correct relative path from that directory.

Contents

• Understanding Rails Generator Template Structure
• Correct Template Placement
• Fixing Your Generator Method
• Alternative Approach: Using Source Paths
• Testing Your Custom Generator
• Common Issues and Solutions

Understanding Rails Generator Template Structure

Rails generators follow a specific directory structure for templates. When you create a custom generator, Rails looks for templates in a specific order:

1. lib/generators/[generator_name]/templates/ - Custom templates specific to your generator
2. lib/generators/rails/scaffold/templates/ - Default Rails scaffold templates
3. lib/generators/erb/scaffold/templates/ - ERB scaffold templates

The standard ERB scaffold templates are located in lib/generators/erb/scaffold/templates/, which corresponds to the path app/lib/generators/templates/erb/scaffold in your Rails application.

When you use the template method in your generator, Rails looks for the file relative to the templates directory of your generator or the default Rails templates.

Correct Template Placement

For your custom _index_row.html.erb.tt template:

1. Place the file in lib/generators/erb/scaffold/templates/ (or app/lib/generators/templates/erb/scaffold in your Rails app)
2. Make sure it follows the naming convention that Rails expects

The standard Rails scaffold templates are located in this directory, and your custom template will be found alongside them when you properly reference it in your generator.

Fixing Your Generator Method

The issue with your current implementation is in how you’re calling the template method. The correct syntax should be:

def generate_row_partial
  template "erb/scaffold/_index_row.html.erb.tt",
    File.join("app/views", plural_name, "_#{singular_name}_row.html.erb")
end

The key changes are:

1. The template path should be relative to the lib/generators directory
2. The destination path should use File.join for proper path construction
3. The template name should include the full relative path from lib/generators

Here’s a complete scaffold generator example with your custom method:

class ScaffoldGenerator < Rails::Generators::NamedBase
  source_root File.expand_path('../templates', __FILE__)

  argument :attributes, type: :array, default: [], banner: "attribute:type"

  hook_for :orm

  # Include your custom method
  def generate_row_partial
    template "erb/scaffold/_index_row.html.erb.tt",
      File.join("app/views", plural_name, "_#{singular_name}_row.html.erb")
  end

  protected

  def banner
    "Creates a scaffolded view, model, and controller for #{class_name}"
  end
end

Alternative Approach: Using Source Paths

If you prefer to keep your custom templates separate from the default Rails templates, you can specify a custom source path in your generator:

class ScaffoldGenerator < Rails::Generators::NamedBase
  source_root File.expand_path('../templates', __FILE__)

  # Add this line to specify a custom source path
  source_paths << File.join(File.dirname(__FILE__), 'templates', 'custom')

  # Your existing code...
  def generate_row_partial
    template "_index_row.html.erb.tt",
      File.join("app/views", plural_name, "_#{singular_name}_row.html.erb")
  end
end

Then place your custom template in lib/generators/scaffold_generator/templates/custom/.

Testing Your Custom Generator

After implementing these changes:

1. Restart your Rails console or server to ensure the generator is reloaded
2. Run your scaffold generator:
   bash

   rails generate scaffold Post title:string content:text
   

3. Check if the partial is created in app/views/posts/_post_row.html.erb

You can also test the generator in development mode with the --pretend flag:

rails generate scaffold Post title:string content:text --pretend

This will show you what files would be created without actually creating them.

Common Issues and Solutions

Issue 1: Generator doesn’t pick up the template

• Ensure the template is in the correct directory
• Verify the case sensitivity matches your system
• Check that you’ve properly included the method in your generator class

Issue 2: Template is found but method isn’t called

• Make sure your method is properly defined within your generator class
• Verify that the method name doesn’t conflict with any Rails generator methods
• Check that the method is being called in the generator’s flow

Issue 3: Path errors when template is in erb/scaffold directory

• Use the full relative path from lib/generators (e.g., erb/scaffold/_index_row.html.erb.tt)
• Avoid absolute paths in the template argument

Issue 4: Template is created in wrong location

• Use File.join for constructing paths to ensure cross-platform compatibility
• Verify the destination path logic matches your desired output structure

Conclusion

Adding custom templates to Rails scaffold generators requires understanding the template lookup path and correctly referencing your templates in the generator code. The key points to remember are:

1. Place your template in the appropriate directory (lib/generators/erb/scaffold/templates/ for ERB templates)
2. Reference the template with its full relative path in the template method
3. Use File.join for constructing destination paths
4. Ensure your custom method is properly defined and called in the generator

With these changes, your custom _index_row.html.erb.tt template should be correctly generated when you run your scaffold generator.