Module: DatastaxRails::Validations::ClassMethods

Defined in:
lib/datastax_rails/validations.rb,
lib/datastax_rails/validations/associated.rb,
lib/datastax_rails/validations/uniqueness.rb

Overview

:nodoc:

Instance Method Summary collapse

Instance Method Details

#create!(attributes = {}) ⇒ Object 



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# File 'lib/datastax_rails/validations.rb', line 17

def create!(attributes = {})
  new(attributes).tap do |object|
    yield(object) if block_given?
    object.save!
  end
end

#validates_associated(*attr_names) ⇒ Object

Validates whether the associated object or objects are all valid themselves. Works with any kind of association.

class Book < DatastaxRails::Base
  has_many :pages
  belongs_to :library

  validates_associated :pages, :library
end

WARNING: This validation must not be used on both ends of an association. Doing so will lead to a circular dependency and cause infinite recursion.

NOTE: This validation will not fail if the association hasn’t been assigned. If you want to ensure that the association is both present and guaranteed to be valid, you also need to use validates_presence_of.

Configuration options:

  • :message - A custom error message (default is: “is invalid”)

  • :on - Specifies when this validation is active. Runs in all validation contexts by default (nil), other options are :create and :update.

  • :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.



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# File 'lib/datastax_rails/validations/associated.rb', line 41

def validates_associated(*attr_names)
  validates_with AssociatedValidator, _merge_attributes(attr_names)
end

#validates_uniqueness_of(*attr_names) ⇒ Object

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 < DatastaxRails::Base
  validates_uniqueness_of :user_name
end

It can also validate whether the value of the specified attributes are unique based on a scope parameter:

class Person < DatastaxRails::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 < DatastaxRails::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.

  • :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).

  • :untokenized_attr - If attr is tokenized, this is the untokenized version to check.

  • :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 DatastaxRails::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!

It is left as an exercise of the developer to figure out how to solve this problem at the application level because there is no way to do so generically since Cassandra doesn’t support UNIQUE indexes.



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# File 'lib/datastax_rails/validations/uniqueness.rb', line 120

def validates_uniqueness_of(*attr_names)
  validates_with UniquenessValidator, _merge_attributes(attr_names)
end