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Rails 5 Passing current record for custom error

on July 13, 2016
This blog is part of our Rails 5 series.

Active Record validations by default provides an error messages, based on applied attributes. But some time we need to display a custom error message while validating a record.

We can give custom error message by passing String or Proc to :message.

1
2class Book < ActiveRecord::Base
3  # error message with a string
4  validates_presence_of :title, message: 'You must provide the title of book.'
5
6  # error message with a proc
7  validates_presence_of :price,
8      :message => Proc.new { |error, attributes|
9      "#{attributes[:key]} cannot be blank."
10      }
11end
12

What's new in Rails 5 ?

Rails 5 allows passing record to error message generator. Now we can pass current record object in a proc as an argument, so that we can write custom error message based on current object.

Revised example with current record object.

1
2class Book < ActiveRecord::Base
3  # error message with simple string
4  validates_presence_of :title, message: 'You must provide the title of book.'
5
6  # error message with proc using current record object
7  validates_presence_of :price,
8      :message => Proc.new { |book, data|
9      "You must provide #{data[:attribute]} for #{book.title}"
10      }
11end
12

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