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== Create a migration generator ==
When you created the plugin above, you specified the --with-generator option, so you already have the generator stubs in your plugin.
We'll be relying on the built-in rails generate template for this tutorial. Going into the details of generators is beyond the scope of this tutorial.
Type:
script/generate
You should see the line:
Plugins (vendor/plugins): yaffle
When you run `script/generate yaffle` you should see the contents of your USAGE file. For this plugin, the USAGE file looks like this:
------------------------------------------------------------------
Description:
Creates a migration that adds yaffle squawk fields to the given model
Example:
./script/generate yaffle hickwall
This will create:
db/migrate/TIMESTAMP_add_yaffle_fields_to_hickwall
------------------------------------------------------------------
Now you can add code to your generator:
[source, ruby]
------------------------------------------------------------------
# File: vendor/plugins/yaffle/generators/yaffle/yaffle_generator.rb
class YaffleGenerator < Rails::Generator::NamedBase
def manifest
record do |m|
m.migration_template 'migration:migration.rb', "db/migrate", {:assigns => yaffle_local_assigns,
:migration_file_name => "add_yaffle_fields_to_#{custom_file_name}"
}
end
end
private
def custom_file_name
custom_name = class_name.underscore.downcase
custom_name = custom_name.pluralize if ActiveRecord::Base.pluralize_table_names
end
def yaffle_local_assigns
returning(assigns = {}) do
assigns[:migration_action] = "add"
assigns[:class_name] = "add_yaffle_fields_to_#{custom_file_name}"
assigns[:table_name] = custom_file_name
assigns[:attributes] = [Rails::Generator::GeneratedAttribute.new("last_squawk", "string")]
assigns[:attributes] << Rails::Generator::GeneratedAttribute.new("last_squawked_at", "datetime")
end
end
end
------------------------------------------------------------------
Note that you need to be aware of whether or not table names are pluralized.
This does a few things:
* Reuses the built in rails `migration_template` method.
* Reuses the built-in rails migration template.
When you run the generator like
script/generate yaffle bird
You will see a new file:
[source, ruby]
------------------------------------------------------------------
# File: db/migrate/20080529225649_add_yaffle_fields_to_birds.rb
class AddYaffleFieldsToBirds < ActiveRecord::Migration
def self.up
add_column :birds, :last_squawk, :string
add_column :birds, :last_squawked_at, :datetime
end
def self.down
remove_column :birds, :last_squawked_at
remove_column :birds, :last_squawk
end
end
------------------------------------------------------------------
|
