DistroPropaganda/code/rails30/e1/ar/lib/migration_helpers.rb

#---
# Excerpted from "Agile Web Development with Rails",
# published by The Pragmatic Bookshelf.
# Copyrights apply to this code. It may not be used to create training material,
# courses, books, articles, and the like. Contact us if you are in doubt.
# We make no guarantees that this code is fit for any purpose.
# Visit http://www.pragmaticprogrammer.com/titles/rails4 for more book information.
#---
#---
# Excerpted from "Agile Web Development with Rails, 4rd Ed.",
# published by The Pragmatic Bookshelf.
# Copyrights apply to this code. It may not be used to create training material, 
# courses, books, articles, and the like. Contact us if you are in doubt.
# We make no guarantees that this code is fit for any purpose. 
# Visit http://www.pragmaticprogrammer.com/titles/rails4 for more book information.
#---
module MigrationHelpers

  def foreign_key(from_table, from_column, to_table)
    constraint_name = "fk_#{from_table}_#{to_table}"

    execute %{
      CREATE TRIGGER #{constraint_name}_insert
      BEFORE INSERT ON #{from_table}
      FOR EACH ROW BEGIN
        SELECT 
	  RAISE(ABORT, "constraint violation: #{constraint_name}")
	WHERE 
	  (SELECT id FROM #{to_table} WHERE id = NEW.#{from_column}) IS NULL;
      END;
    }

    execute %{
      CREATE TRIGGER #{constraint_name}_update
      BEFORE UPDATE ON #{from_table}
      FOR EACH ROW BEGIN
        SELECT 
	  RAISE(ABORT, "constraint violation: #{constraint_name}")
	WHERE 
	  (SELECT id FROM #{to_table} WHERE id = NEW.#{from_column}) IS NULL;
      END;
    }

    execute %{
      CREATE TRIGGER #{constraint_name}_delete
      BEFORE DELETE ON #{to_table}
      FOR EACH ROW BEGIN
        SELECT 
	  RAISE(ABORT, "constraint violation: #{constraint_name}")
	WHERE 
	  (SELECT id FROM #{from_table} WHERE #{from_column} = OLD.id) IS NOT NULL;
      END;
    }
  end

end