From 638333b7a17234ed65b2e8b0bee3d9b533446803 Mon Sep 17 00:00:00 2001 From: Pratik Naik Date: Thu, 19 Mar 2009 23:36:08 +0000 Subject: Move uniqueness and association validations to Active Record --- .../lib/active_record/validations/uniqueness.rb | 159 +++++++++++++++++++++ 1 file changed, 159 insertions(+) create mode 100644 activerecord/lib/active_record/validations/uniqueness.rb (limited to 'activerecord/lib/active_record/validations/uniqueness.rb') diff --git a/activerecord/lib/active_record/validations/uniqueness.rb b/activerecord/lib/active_record/validations/uniqueness.rb new file mode 100644 index 0000000000..edec4e9e43 --- /dev/null +++ b/activerecord/lib/active_record/validations/uniqueness.rb @@ -0,0 +1,159 @@ +module ActiveRecord + module Validations + 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, :scope => :account_id + # end + # + # It can also validate whether the value of the specified attributes are unique based on 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 + # + # 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: + # * :message - Specifies a custom error message (default is: "has already been taken"). + # * :scope - One or more columns by which to limit the scope of the uniqueness constraint. + # * :case_sensitive - Looks for an exact match. Ignored by non-text columns (+true+ by default). + # * :allow_nil - If set to true, skips this validation if the attribute is +nil+ (default is +false+). + # * :allow_blank - If set to true, skips this validation if the attribute is blank (default is +false+). + # * :if - Specifies a method, proc or string to call to determine if the validation should + # occur (e.g. :if => :allow_validation, or :if => Proc.new { |user| user.signup_step > 2 }). The + # method, proc or string should return or evaluate to a true or false value. + # * :unless - Specifies a method, proc or string to call to determine if the validation should + # not occur (e.g. :unless => :skip_validation, or :unless => Proc.new { |user| user.signup_step <= 2 }). 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 + # 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 his title is unique. + # | SELECT * FROM comments + # | WHERE title = 'My Post' + # | + # # User 1 inserts his 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! + # + # This could even happen if you use transactions with the 'serializable' + # isolation level. There are several ways to get around this problem: + # - By locking the database table before validating, and unlocking it after + # saving. However, table locking is very expensive, and thus not + # recommended. + # - By locking a lock file before validating, and unlocking it after saving. + # This does not work if you've scaled your Rails application across + # multiple web servers (because they cannot share lock files, or cannot + # do that efficiently), and thus not recommended. + # - Creating a unique index on the field, by using + # ActiveRecord::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 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 him to re-enter the title). + # This technique is also known as optimistic concurrency control: + # http://en.wikipedia.org/wiki/Optimistic_concurrency_control + # + # Active Record currently provides no way to distinguish unique + # index constraint errors from other types of database errors, so you + # will have to parse the (database-specific) exception message to detect + # such a case. + def validates_uniqueness_of(*attr_names) + configuration = { :case_sensitive => true } + configuration.update(attr_names.extract_options!) + + validates_each(attr_names,configuration) do |record, attr_name, value| + # 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. + class_hierarchy = [record.class] + while class_hierarchy.first != self + class_hierarchy.insert(0, class_hierarchy.first.superclass) + end + + # Now we can work our way down the tree to the first non-abstract + # class (which has a database table to query from). + finder_class = class_hierarchy.detect { |klass| !klass.abstract_class? } + + column = finder_class.columns_hash[attr_name.to_s] + + if value.nil? + comparison_operator = "IS ?" + elsif column.text? + comparison_operator = "#{connection.case_sensitive_equality_operator} ?" + value = column.limit ? value.to_s[0, column.limit] : value.to_s + else + comparison_operator = "= ?" + end + + sql_attribute = "#{record.class.quoted_table_name}.#{connection.quote_column_name(attr_name)}" + + if value.nil? || (configuration[:case_sensitive] || !column.text?) + condition_sql = "#{sql_attribute} #{comparison_operator}" + condition_params = [value] + else + condition_sql = "LOWER(#{sql_attribute}) #{comparison_operator}" + condition_params = [value.mb_chars.downcase] + end + + if scope = configuration[:scope] + Array(scope).map do |scope_item| + scope_value = record.send(scope_item) + condition_sql << " AND " << attribute_condition("#{record.class.quoted_table_name}.#{scope_item}", scope_value) + condition_params << scope_value + end + end + + unless record.new_record? + condition_sql << " AND #{record.class.quoted_table_name}.#{record.class.primary_key} <> ?" + condition_params << record.send(:id) + end + + finder_class.with_exclusive_scope do + if finder_class.exists?([condition_sql, *condition_params]) + record.errors.add(attr_name, :taken, :default => configuration[:message], :value => value) + end + end + end + end + end + end +end -- cgit v1.2.3