Schema Validations is a plugin that reads various constraints defined against columns in your database and applies the closest matching rails validation. (Ala Dave Thomas’ Keynote.)

Over and above installing the plugin, no further action is required for the validations to take effect; the database schema constraints will be read and applied as validations when your ActiveRecord model classes are loaded; just like magic.

The plugin supports the following constraints:

• NOT NULL is converted to validates_presence_of (including belongs_to associations);
• Numbers are checked using validates_numericality_of (including :only_integer => true);
• String lengths are checked using validates_length_of;
• Single-column unique indexes are converted to validates_uniqueness_of; and
• Multi-column unique indexes are converted to validates_uniqueness_of with scope.

For multi-column unique indexes the column validated for uniqueness is either the last column not ending in ‘_id’ or simply the last column. This follows the typical composite unique index column ordering where the scoping is specified first but will attempt to find the last non-foreign-key column just-in-case. Eg, both add_index :states, [:country_id, :name] and add_index :states, [:name, :country_id] would result in validates_uniqueness_of :name, :scope => [:country_id].

=== Dependencies

• RedHill on Rails Core (redhillonrails_core).