Rails parse @import Less files from database

I want to parse less type content from database and store the result css in other column. I'm using the less-rails gem.

I have a Template model where I store the name, less_content & css_content

So far I have done this in a before_save callback:

 def less_parser
      parser = Less::Parser.new
      self.css_content = parser.parse(self.less_content).to_css
  end

This works very well. But the problem are the @import variables of less. If I write @import "file_name".

I get the following error:

Less::Error - 'file_name.less' wasn't found:
  less (2.6.0) lib/less/parser.rb:74:in `block (2 levels) in parse'
  at finish (/Users/Artau/.rbenv/versions/2.2.0/lib/ruby/gems/2.2.0/gems/less-2.6.0/lib/less/js/lib/less/parser.js:666:in `'
  at tree.importVisitor.run (/Users/Artau/.rbenv/versions/2.2.0/lib/ruby/gems/2.2.0/gems/less-2.6.0/lib/less/js/lib/less/import-visitor.js:34:in `'
  at Parser.parser.parse (/Users/Artau/.rbenv/versions/2.2.0/lib/ruby/gems/2.2.0/gems/less-2.6.0/lib/less/js/lib/less/parser.js:675:in `'
  less (2.6.0) lib/less/parser.rb:64:in `block in parse'
  less (2.6.0) lib/less/java_script/v8_context.rb:90:in `block in do_lock'
  less (2.6.0) lib/less/java_script/v8_context.rb:88:in `call'
  less (2.6.0) lib/less/java_script/v8_context.rb:88:in `Locker'
  less (2.6.0) lib/less/java_script/v8_context.rb:88:in `do_lock'
  less (2.6.0) lib/less/java_script/v8_context.rb:60:in `lock'
  less (2.6.0) lib/less/java_script/v8_context.rb:30:in `exec'
  less (2.6.0) lib/less/java_script.rb:26:in `exec'
  less (2.6.0) lib/less/parser.rb:63:in `parse'
  app/models/template.rb:32:in `less_parser'

Obviously I need to tell the Less::Parser where the file is. But I don't know how to do that.