dm-validations proposal for a better command query seperation

gistfile1.md

Traditional

resource = Resource.new attributes
resource.valid?                  # => true | false
resource.save                    # => true | false Will raise adapter errors in case of Inconsistency
resource.errors                  # => ErrorSet (cached) will not reflect adapter errors
resource.attribute=invalid_value
resource.errors                  # Same error Set as above, will not reflect attribute change

Problems:

• Command query seperation is low
• Errors must not reflect the latest validation results
• No central point to catch exceptions from adapters

New interface ExternalValidationState (mbj)

Naming is not authoritative.

The traditional API is left untouched. Only Resource#validate will be called more often.

• ErrorSet will be upgraded to something like ValidationState
• Resource#valid? is implemented as resource.validate.valid?
• Resource#errors is aliased to Resource#validate, it does not cache anymore
• Resource#{save,delete,update} is left untouched
• before :valid? will be depreciated. IMHO it hides bad model design.
• No way to navigate from a resource to an outdated validation result anymore.

resource = Resource.new attributes
state = resource.validate    # Resource#validate returns a more powerful ErrorSet (ValidationState?)
# This state carries the same information like #errors before, 
# but can also be responsible to persist the resource with 
# adapter exception converison.
state.save                   # => true | false

Store errors in PersistenceState (emdash)

Emmanuel: Pls enter your idea here!!!

validation_set.rb

# This ValidationState has exactly the same interface like ErrorSet plus a few additions for persistance.

class ValidationState
  # Paste implementation of ErrorSet HERE
  alias :valid? :empty?

  def save
    return false unless valid?
    begin
      return resource.save
    rescue ListOfAdapterSpecificConfigurableExceptions => exception
      add(transform_exception(exception))
      false
    end
  end

  private

  def transform_exception(exception)
    if exception.respond_to?(:foo)
      Violation.new(resource,exception.foo)
    else
      Violation.new(resource,"repository error: #{exception.message}")
    end
  end
end