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Library for performing validations on DM models and pure Ruby object
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This is a DataMapper plugin that provides validations for DataMapper model classes.

Setup

DataMapper validation capabilities are automatically available for DataMapper resources when you require dm-validations' into your application. For pure Ruby classes, require 'dm-validations' and then include DataMapper::Validate module like so:

class ProgrammingLanguage

#
# Behaviors
#

include ::DataMapper::Validate

#
# Accessors
#

attr_accessor :name, :allows_manual_memory_management, :allows_optional_parentheses

#
# Validations
#

validates_present :name
validates_with_method :ensure_allows_optional_parentheses,     :when => [:implementing_a_dsl]
validates_with_method :ensure_allows_manual_memory_management, :when => [:doing_system_programming]

end

Specifying Model Validations

There are two primary ways to implement validations for your models:

1) Placing validation methods with properties as params in your class

definitions like:
- validates_length :name
- validates_length [:name, :description]

2) Using auto-validations, please see DataMapper::Validate::AutoValidate

An example class with validations declared:

require 'dm-validations'

class Account
  include DataMapper::Resource

  property :name, String
  validates_length :name
end

See all of the DataMapper::Validate module's XYZValidator(s) to learn about the complete collections of validators available to you.

Validating

DataMapper validations, when included, alter the default save/create/update process for a model. Unless you specify a context the resource must be valid in the :default context before saving.

You may manually validate a resource using the valid? method, which will return true if the resource is valid, and false if it is invalid.

In addition to the valid? method, there is also an all_valid? method that recursively walks both the current object and its associated objects and returns its true/false result for the entire walk.

Working with Validation Errors

If your validators find errors in your model, they will populate the DataMapper::Validate::ValidationErrors object that is available through each of your models via calls to your model's errors method.

For example:

my_account = Account.new(:name => "Jose")
if my_account.save
  # my_account is valid and has been saved
else
  my_account.errors.each do |e|
    puts e
  end
end

See DataMapper::Validate::ValidationErrors for all you can do with your model's errors method.

Contextual Validations

DataMapper Validations also provide a means of grouping your validations into contexts. This enables you to run different sets of validations when you need it. For instance, the same model may not only behave differently when initially saved or saved on update, but also require special validation sets for publishing, exporting, importing and so on.

Again, using our example for pure Ruby class validations:

class ProgrammingLanguage

#
# Behaviors
#

include ::DataMapper::Validate

#
# Accessors
#

attr_accessor :name, :allows_manual_memory_management, :allows_optional_parentheses

#
# Validations
#

validates_present :name
validates_with_method :ensure_allows_optional_parentheses,     :when => [:implementing_a_dsl]
validates_with_method :ensure_allows_manual_memory_management, :when => [:doing_system_programming]

end

ProgrammingLanguage instance now use #valid? method with one of two context symbols:

@ruby.valid?(:implementing_a_dsl) # => true @ruby.valid?(:doing_system_programming) # => false

@c.valid?(:implementing_a_dsl) # => false @c.valid?(:doing_system_programming) # => true

Each context causes different set of validations to be triggered. If you don't specify a context using :when, :on or :group options (they are all aliases and do the same thing), default context name is :default. When you do model.valid? (without specifying context explicitly), again, :default context is used. One validation can be used in two, three or five contexts if you like:

class Book

#
# Behaviors
#

# this time it is a DM model
include ::DataMapper::Resource

#
# Accessors
#

property :id,           Serial
property :name,         String

property :agreed_title, String
property :finished_toc, Boolean

#
# Validations
#

# used in all contexts, including default
validates_present :name,         :when => [:default, :sending_to_print]
validates_present :agreed_title, :when => [:sending_to_print]

validates_with_block :toc, :when => [:sending_to_print] do
  if self.finished_toc
    [true]
  else
    [false, "TOC must be finalized before you send a book to print"]
  end
end

end

In the example above, name is validated for presence in both :default context and :sending_to_print context, while TOC related block validation and title presence validation only take place in :sending_to_print context.

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