Custom validation methods in Ruby on Rails - Step-by-Step Execution

Concept Flow - Custom validation methods

Start: Model instance created

↓

Call validate method

↓

Run custom validation method

↓

Check condition inside method

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No error

↓

Validation result

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Save or reject model

When saving a model, Rails calls custom validation methods that check conditions and add errors if needed, deciding if the model is valid.

Execution Sample

Ruby on Rails

class User < ApplicationRecord
  validate :email_must_be_company

  def email_must_be_company
    unless email&.end_with?('@company.com')
      errors.add(:email, 'must be a company email')
    end
  end
end

This code checks if a user's email ends with '@company.com' and adds an error if it doesn't.

Execution Table

Step	Action	Condition Checked	Result	Errors Added
1	Create User instance with email '[e-mail]'	N/A	Instance created	None
2	Call validate method on User	N/A	Custom validation method called	None
3	Check if email ends with '@company.com'	email = '[e-mail]'	False	Add error: 'email must be a company email'
4	Validation result	Errors present?	Yes	User invalid, save rejected
5	Create User instance with email '[e-mail]'	N/A	Instance created	None
6	Call validate method on User	N/A	Custom validation method called	None
7	Check if email ends with '@company.com'	email = '[e-mail]'	True	No error added
8	Validation result	Errors present?	No	User valid, save allowed

💡 Validation stops after checking condition; errors determine if save proceeds.

Variable Tracker

Variable	Start	After Step 3	After Step 7	Final
email	N/A	'[e-mail]'	'[e-mail]'	Depends on instance
errors	Empty	Contains error for email	Empty	Depends on instance
validation_result	N/A	Invalid	Valid	Depends on instance

Key Moments - 2 Insights

Why does the validation fail for '[e-mail]' but pass for '[e-mail]'?

Because the custom method checks if the email ends with '@company.com'. At step 3, '[e-mail]' fails this check and adds an error, while at step 7, '[e-mail]' passes and adds no error.

What happens if the email is nil or empty?

The method uses safe navigation (&.) to avoid errors. If email is nil, the condition returns false, so an error is added, preventing save.

Visual Quiz - 3 Questions

Look at the execution table, what error is added at step 3?

A 'email cannot be blank'

B 'email is invalid format'

C 'email must be a company email'

D No error added

💡 Hint

Check the 'Errors Added' column at step 3 in the execution table.

At which step does the validation method confirm the email is valid?

A Step 7

B Step 3

C Step 4

D Step 8

💡 Hint

Look for the step where the condition is true and no errors are added.

If the email was '[e-mail]', what would happen at step 3?

A No error added, validation passes

B Error added, validation fails

C Method raises an exception

D Validation skipped

💡 Hint

The method checks if email ends with '@company.com'; '[e-mail]' does not.

Concept Snapshot

Custom validation methods in Rails let you add your own checks inside models.
Define a method that adds errors if conditions fail.
Use 'validate :method_name' to run it during validation.
If errors are added, the model is invalid and won't save.
Use safe checks to avoid errors with nil values.

Full Transcript

In Rails, custom validation methods let you check specific rules for your model data. When you save a model, Rails calls these methods. Inside the method, you check a condition, like if an email ends with '@company.com'. If it doesn't, you add an error message. This error stops the model from saving. For example, if a user has '[e-mail]', the validation adds an error and save fails. But if the email is '[e-mail]', no error is added and save succeeds. This process helps keep your data clean and correct.