Validations in Ruby on rails

Validations are used to ensure that only valid data is saved into your database. For example, it may be important to your application to ensure that every user provides a valid email address and mailing address. Need for validations

• Database constraints and/or stored procedures make the validation mechanisms database-dependent and can make testing and maintenance more difficult. However, if your database is used by other applications, it may be a good idea to use some constraints at the database level. Additionally, database-level validations can safely handle some things can be difficult to implement otherwise.

• Client-side validations can be useful, but are generally unreliable if used alone. If they are implemented using JavaScript, they may be bypassed if JavaScript is turned off in the user’s browser. However, if combined with other techniques, client-side validation can be a convenient way to provide users with immediate feedback as they use your site.

• Controller-level validations can be tempting to use, but often become unwieldy and difficult to test and maintain. Whenever possible, it’s a good idea to keep your controllers skinny, as it will make your application a pleasure to work with in the long run.

• Model-level validations are the best way to ensure that only valid data is saved into your database. They are database agnostic, cannot be bypassed by end users, and are convenient to test and maintain. Rails makes them easy to use, provides built-in helpers for common needs, and allows you to create your own validation methods as well.

Validation Story

The following methods skip validations, and will save the object to the database regardless of its validity. They should be used with caution.

• decrement!
• decrement_counter
• increment!
• increment_counter
• toggle!
• update_all
• update_attribute
• update_counters

Validation Helpers

Active Record offers many pre-defined validation helpers that you can use directly inside your class definitions. These helpers provide common validation rules. Every time a validation fails, an error message is added to the object’s errors collection, and this message is associated with the field being validated.

Each helper accepts an arbitrary number of attribute names, so with a single line of code you can add the same kind of validation to several attributes.

All of them accept the :on and :message options, which define when the validation should be run and what message should be added to the errors collection if it fails, respectively. The :on option takes one of the values :save (the default), :create or :update. There is a default error message for each one of the validation helpers. These messages are used when the :message option isn’t specified. Let’s take a look at each one of the available helpers.

1.validates_confirmation_of 2.validates_exclusion_of 3.validates_format_of 4.validates_length_of 5.validates_numericality_of 6.validates_uniqueness_of 7.validates_each