Ruby-on-rails – Can Rails Routing Helpers (i.e. themodel_path(model)) be Used in Models

helpermethodsrails-routingruby-on-rails

Say I have a Rails Model called Thing. Thing has a url attribute that can optionally be set to a URL somewhere on the Internet. In view code, I need logic that does the following:

<% if thing.url.blank? %>
<%= link_to('Text', thing_path(thing)) %>
<% else %>
<%= link_to('Text', thing.url) %>
<% end %>

This conditional logic in the view is ugly. Of course, I could build a helper function, which would change the view to this:

<%= thing_link('Text', thing) %>

That solves the verbosity problem, but I would really prefer having the functionality in the model itself. In which case, the view code would be:

<%= link_to('Text', thing.link) %>

This, obviously, would require a link method on the model. Here's what it would need to contain:

def link
  (self.url.blank?) ? thing_path(self) : self.url
end

To the point of the question, thing_path() is an undefined method inside Model code. I'm assuming it's possible to "pull in" some helper methods into the model, but how? And is there a real reason that routing only operates at the controller and view layers of the app? I can think of lots of cases where model code may need to deal with URLs (integrating with external systems, etc).

Best Answer

In Rails 3 and higher:

Rails.application.routes.url_helpers

e.g.

Rails.application.routes.url_helpers.posts_path
Rails.application.routes.url_helpers.posts_url(:host => "example.com")

Related Solutions

Ruby-on-rails – Rails: How to rename a database column in a Ruby on Rails migration

rename_column :table, :old_column, :new_column

You'll probably want to create a separate migration to do this. (Rename FixColumnName as you will.):

script/generate migration FixColumnName
# creates  db/migrate/xxxxxxxxxx_fix_column_name.rb

Then edit the migration to do your will:

# db/migrate/xxxxxxxxxx_fix_column_name.rb
class FixColumnName < ActiveRecord::Migration
  def self.up
    rename_column :table_name, :old_column, :new_column
  end

  def self.down
    # rename back if you need or do something else or do nothing
  end
end

For Rails 3.1 use:

While, the up and down methods still apply, Rails 3.1 receives a change method that "knows how to migrate your database and reverse it when the migration is rolled back without the need to write a separate down method".

See "Active Record Migrations" for more information.

rails g migration FixColumnName

class FixColumnName < ActiveRecord::Migration
  def change
    rename_column :table_name, :old_column, :new_column
  end
end

If you happen to have a whole bunch of columns to rename, or something that would have required repeating the table name over and over again:

rename_column :table_name, :old_column1, :new_column1
rename_column :table_name, :old_column2, :new_column2
...

You could use change_table to keep things a little neater:

class FixColumnNames < ActiveRecord::Migration
  def change
    change_table :table_name do |t|
      t.rename :old_column1, :new_column1
      t.rename :old_column2, :new_column2
      ...
    end
  end
end

Then just db:migrate as usual or however you go about your business.

For Rails 4:

While creating a Migration for renaming a column, Rails 4 generates a change method instead of up and down as mentioned in the above section. The generated change method is:

$ > rails g migration ChangeColumnName

which will create a migration file similar to:

class ChangeColumnName < ActiveRecord::Migration
  def change
    rename_column :table_name, :old_column, :new_column
  end
end

Best Answer

Related Solutions

Ruby-on-rails – Rails: How to rename a database column in a Ruby on Rails migration

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