diff options
| -rw-r--r-- | activerecord/lib/active_record/validations/uniqueness.rb | 42 |
1 files changed, 17 insertions, 25 deletions
diff --git a/activerecord/lib/active_record/validations/uniqueness.rb b/activerecord/lib/active_record/validations/uniqueness.rb index cb1d2ae421..a25558bd80 100644 --- a/activerecord/lib/active_record/validations/uniqueness.rb +++ b/activerecord/lib/active_record/validations/uniqueness.rb @@ -154,33 +154,25 @@ module ActiveRecord # | # title! # # This could even happen if you use transactions with the 'serializable' - # isolation level. There are several ways to get around this problem: + # isolation level. The best way to work around this problem is to add a unique + # index to the database table using + # ActiveRecord::ConnectionAdapters::SchemaStatements#add_index. In the + # rare case that a race condition occurs, the database will guarantee + # the field's uniqueness. # - # - 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 # - # 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. + # 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) validates_with UniquenessValidator, _merge_attributes(attr_names) |