Hi Friends,
Today we will be going to discuss a very basic constraint of rails validation that is uniqueness, as its name suggests, Unique Validator is a rails validation helper used to check an attribute value in database and if it already exists, the duplicate value will not be saved.
It has a scope helper which is used to specify some extra constraints that limits the scope to a particular condition as per requirement.
It also has a case_sensitive helper to check whether the uniqueness would be case sensitive or not.

Example:

class Blog < ActiveRecord::Base
  validates :title, uniqueness: true    
end

class Blog < ActiveRecord::Base
  validates :title, uniqueness: { case_sensitive: false }
end

Example (with scope):

class Bonus < ActiveRecord::Base
  validates :emp_id, uniqueness: { scope: :year,
             message: "Can be given only once in a year"}
end

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