activerecord/lib/active_record/validations/uniqueness.rb
# frozen_string_literal: true
module ActiveRecord
module Validations
class UniquenessValidator < ActiveModel::EachValidator # :nodoc:
def initialize(options)
if options[:conditions] && !options[:conditions].respond_to?(:call)
raise ArgumentError, "#{options[:conditions]} was passed as :conditions but is not callable. " \
"Pass a callable instead: `conditions: -> { where(approved: true) }`"
end
unless Array(options[:scope]).all? { |scope| scope.respond_to?(:to_sym) }
raise ArgumentError, "#{options[:scope]} is not supported format for :scope option. " \
"Pass a symbol or an array of symbols instead: `scope: :user_id`"
end
super
@klass = options[:class]
end
def validate_each(record, attribute, value)
finder_class = find_finder_class_for(record)
value = map_enum_attribute(finder_class, attribute, value)
return if record.persisted? && !validation_needed?(finder_class, record, attribute)
relation = build_relation(finder_class, attribute, value)
if record.persisted?
if finder_class.primary_key
relation = relation.where.not(finder_class.primary_key => [record.id_in_database])
else
raise UnknownPrimaryKey.new(finder_class, "Cannot validate uniqueness for persisted record without primary key.")
end
end
relation = scope_relation(record, relation)
if options[:conditions]
conditions = options[:conditions]
relation = if conditions.arity.zero?
relation.instance_exec(&conditions)
else
relation.instance_exec(record, &conditions)
end
end
if relation.exists?
error_options = options.except(:case_sensitive, :scope, :conditions)
error_options[:value] = value
record.errors.add(attribute, :taken, **error_options)
end
end
private
# The check for an existing value should be run from a class that
# isn't abstract. This means working down from the current class
# (self), to the first non-abstract class. Since classes don't know
# their subclasses, we have to build the hierarchy between self and
# the record's class.
def find_finder_class_for(record)
class_hierarchy = [record.class]
while class_hierarchy.first != @klass
class_hierarchy.unshift(class_hierarchy.first.superclass)
end
class_hierarchy.detect { |klass| !klass.abstract_class? }
end
def validation_needed?(klass, record, attribute)
return true if options[:conditions] || options.key?(:case_sensitive)
scope = Array(options[:scope])
attributes = scope + [attribute]
attributes = resolve_attributes(record, attributes)
return true if attributes.any? { |attr| record.attribute_changed?(attr) ||
record.read_attribute(attr).nil? }
!covered_by_unique_index?(klass, record, attribute, scope)
end
def covered_by_unique_index?(klass, record, attribute, scope)
@covered ||= self.attributes.map(&:to_s).select do |attr|
attributes = scope + [attr]
attributes = resolve_attributes(record, attributes)
klass.schema_cache.indexes(klass.table_name).any? do |index|
index.unique &&
index.where.nil? &&
(Array(index.columns) - attributes).empty?
end
end
@covered.include?(attribute.to_s)
end
def resolve_attributes(record, attributes)
attributes.flat_map do |attribute|
reflection = record.class._reflect_on_association(attribute)
if reflection.nil?
attribute.to_s
elsif reflection.polymorphic?
[reflection.foreign_key, reflection.foreign_type]
else
reflection.foreign_key
end
end
end
def build_relation(klass, attribute, value)
relation = klass.unscoped
# TODO: Add case-sensitive / case-insensitive operators to Arel
# to no longer need to checkout a connection here.
comparison = klass.with_connection do |connection|
relation.bind_attribute(attribute, value) do |attr, bind|
return relation.none! if bind.unboundable?
if !options.key?(:case_sensitive) || bind.nil?
connection.default_uniqueness_comparison(attr, bind)
elsif options[:case_sensitive]
connection.case_sensitive_comparison(attr, bind)
else
# will use SQL LOWER function before comparison, unless it detects a case insensitive collation
connection.case_insensitive_comparison(attr, bind)
end
end
end
relation.where!(comparison)
end
def scope_relation(record, relation)
Array(options[:scope]).each do |scope_item|
scope_value = if record.class._reflect_on_association(scope_item)
record.association(scope_item).reader
else
record.read_attribute(scope_item)
end
relation = relation.where(scope_item => scope_value)
end
relation
end
def map_enum_attribute(klass, attribute, value)
mapping = klass.defined_enums[attribute.to_s]
value = mapping[value] if value && mapping
value
end
end
module ClassMethods
# Validates whether the value of the specified attributes are unique
# across the system. Useful for making sure that only one user
# can be named "davidhh".
#
# class Person < ActiveRecord::Base
# validates_uniqueness_of :user_name
# end
#
# It can also validate whether the value of the specified attributes are
# unique based on a <tt>:scope</tt> parameter:
#
# class Person < ActiveRecord::Base
# validates_uniqueness_of :user_name, scope: :account_id
# end
#
# Or even multiple scope parameters. For example, making sure that a
# teacher can only be on the schedule once per semester for a particular
# class.
#
# class TeacherSchedule < ActiveRecord::Base
# validates_uniqueness_of :teacher_id, scope: [:semester_id, :class_id]
# end
#
# It is also possible to limit the uniqueness constraint to a set of
# records matching certain conditions. In this example archived articles
# are not being taken into consideration when validating uniqueness
# of the title attribute:
#
# class Article < ActiveRecord::Base
# validates_uniqueness_of :title, conditions: -> { where.not(status: 'archived') }
# end
#
# To build conditions based on the record's state, define the conditions
# callable with a parameter, which will be the record itself. This
# example validates the title is unique for the year of publication:
#
# class Article < ActiveRecord::Base
# validates_uniqueness_of :title, conditions: ->(article) {
# published_at = article.published_at
# where(published_at: published_at.beginning_of_year..published_at.end_of_year)
# }
# end
#
# When the record is created, a check is performed to make sure that no
# record exists in the database with the given value for the specified
# attribute (that maps to a column). When the record is updated,
# the same check is made but disregarding the record itself.
#
# Configuration options:
#
# * <tt>:message</tt> - Specifies a custom error message (default is:
# "has already been taken").
# * <tt>:scope</tt> - One or more columns by which to limit the scope of
# the uniqueness constraint.
# * <tt>:conditions</tt> - Specify the conditions to be included as a
# <tt>WHERE</tt> SQL fragment to limit the uniqueness constraint lookup
# (e.g. <tt>conditions: -> { where(status: 'active') }</tt>).
# * <tt>:case_sensitive</tt> - Looks for an exact match. Ignored by
# non-text columns. The default behavior respects the default database collation.
# * <tt>:allow_nil</tt> - If set to +true+, skips this validation if the
# attribute is +nil+ (default is +false+).
# * <tt>:allow_blank</tt> - If set to +true+, skips this validation if the
# attribute is blank (default is +false+).
# * <tt>:if</tt> - Specifies a method, proc, or string to call to determine
# if the validation should occur (e.g. <tt>if: :allow_validation</tt>,
# or <tt>if: Proc.new { |user| user.signup_step > 2 }</tt>). The method,
# proc or string should return or evaluate to a +true+ or +false+ value.
# * <tt>:unless</tt> - Specifies a method, proc, or string to call to
# determine if the validation should not occur (e.g. <tt>unless: :skip_validation</tt>,
# or <tt>unless: Proc.new { |user| user.signup_step <= 2 }</tt>). The
# method, proc, or string should return or evaluate to a +true+ or +false+
# value.
#
# === Concurrency and integrity
#
# Using this validation method in conjunction with
# {ActiveRecord::Base#save}[rdoc-ref:Persistence#save]
# does not guarantee the absence of duplicate record insertions, because
# uniqueness checks on the application level are inherently prone to race
# conditions. For example, suppose that two users try to post a Comment at
# the same time, and a Comment's title must be unique. At the database-level,
# the actions performed by these users could be interleaved in the following manner:
#
# User 1 | User 2
# ------------------------------------+--------------------------------------
# # User 1 checks whether there's |
# # already a comment with the title |
# # 'My Post'. This is not the case. |
# SELECT * FROM comments |
# WHERE title = 'My Post' |
# |
# | # User 2 does the same thing and also
# | # infers that their title is unique.
# | SELECT * FROM comments
# | WHERE title = 'My Post'
# |
# # User 1 inserts their comment. |
# INSERT INTO comments |
# (title, content) VALUES |
# ('My Post', 'hi!') |
# |
# | # User 2 does the same thing.
# | INSERT INTO comments
# | (title, content) VALUES
# | ('My Post', 'hello!')
# |
# | # ^^^^^^
# | # Boom! We now have a duplicate
# | # title!
#
# The best way to work around this problem is to add a unique index to the database table using
# {connection.add_index}[rdoc-ref:ConnectionAdapters::SchemaStatements#add_index].
# In the rare case that a race condition occurs, the database will guarantee
# the field's uniqueness.
#
# When the database catches such a duplicate insertion,
# {ActiveRecord::Base#save}[rdoc-ref:Persistence#save] will raise an ActiveRecord::StatementInvalid
# exception. You can either choose to let this error propagate (which
# will result in the default \Rails exception page being shown), or you
# can catch it and restart the transaction (e.g. by telling the user
# that the title already exists, and asking them to re-enter the title).
# This technique is also known as
# {optimistic concurrency control}[https://en.wikipedia.org/wiki/Optimistic_concurrency_control].
#
# The bundled ActiveRecord::ConnectionAdapters distinguish unique index
# constraint errors from other types of database errors by throwing an
# ActiveRecord::RecordNotUnique exception. For other adapters you will
# have to parse the (database-specific) exception message to detect such
# a case.
#
# The following bundled adapters throw the ActiveRecord::RecordNotUnique exception:
#
# * ActiveRecord::ConnectionAdapters::Mysql2Adapter.
# * ActiveRecord::ConnectionAdapters::TrilogyAdapter.
# * ActiveRecord::ConnectionAdapters::SQLite3Adapter.
# * ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.
def validates_uniqueness_of(*attr_names)
validates_with UniquenessValidator, _merge_attributes(attr_names)
end
end
end
end