Create custom template loaders

Marten has built-in support for common template loaders, but the framework also allows you to write your own template loader that you can leverage as part of your project's templates.

Defining a template loaders

Template loaders are subclasses of the Marten::Template::Loader::Base abstract class. They must implement a single #get_template_source method: this method returns the raw content of a template from a provided template name.

For example, rendering the template content.html with a file system loader initialised with Marten::Template::Loader::FileSystem.new("/app/custom_dir/templates") would return the content defined in /app/custom_dir/templates/content.html.

Let's say we want to write a DatabaseTemplate template loader: we first have to define a new class which inherits from Marten::Template::Loader::Base. This new class needs to define a #get_template_source method which takes a template_name string argument and also returns a string.

For simplicity we assume that there already exists an HtmlTemplate model, featuring a name field and content field:

class DatabaseTemplate < Marten::Template::Loader::Base
  def get_template_source(template_name) : String
    begin
      return HtmlTemplate.get!(name: template_name).content!
    rescue e : Marten::DB::Errors::RecordNotFound
      raise Marten::Template::Errors::TemplateNotFound.new("Template #{template_name} could not be found ; #{e.message}", e)
    end
  end
end