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".
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.
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.
Because this check is performed outside the database there is still a
chance that duplicate values will be inserted in two parallel transactions.
To guarantee against this you should create a unique index on the field.
See add_index for more information.
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 (false 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.
# File activemodel/lib/active_model/validations/uniqueness.rb, line 37
def validates_uniqueness_of(*attr_names)
configuration = { :message => ActiveRecord::Errors.default_error_messages[:taken] }
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? }
if value.nil? || (configuration[:case_sensitive] || !finder_class.columns_hash[attr_name.to_s].text?)
condition_sql = "#{record.class.quoted_table_name}.#{attr_name} #{attribute_condition(value)}"
condition_params = [value]
else
# sqlite has case sensitive SELECT query, while MySQL/Postgresql don't.
# Hence, this is needed only for sqlite.
condition_sql = "LOWER(#{record.class.quoted_table_name}.#{attr_name}) #{attribute_condition(value)}"
condition_params = [value.downcase]
end
if scope = configuration[:scope]
Array(scope).map do |scope_item|
scope_value = record.send(scope_item)
condition_sql << " AND #{record.class.quoted_table_name}.#{scope_item} #{attribute_condition(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
results = finder_class.with_exclusive_scope do
connection.select_all(
construct_finder_sql(
:select => "#{attr_name}",
:from => "#{finder_class.quoted_table_name}",
:conditions => [condition_sql, *condition_params]
)
)
end
unless results.length.zero?
found = true
# As MySQL/Postgres don't have case sensitive SELECT queries, we try to find duplicate
# column in ruby when case sensitive option
if configuration[:case_sensitive] && finder_class.columns_hash[attr_name.to_s].text?
found = results.any? { |a| a[attr_name.to_s] == value }
end
record.errors.add(attr_name, configuration[:message]) if found
end
end
end
1Note
:case_sensitive is on by default?
FooBarWidget ยท Jul 1, 20083 thanks
In contrast to what the documentation said, :case_sensitive seems to be on by default. This is the case with MySQL at least, I'm not sure about other databases.
