DM1 example of using RefCode DM custom property (useful for avoiding outside exposure of internal ids) w/ RetrySaveMixin

1_DM_refcode_type.rb

require 'digest/sha1'

class RefCode < ::DataMapper::Property::String
    required     true
    unique_index true
    default      proc { |_, prop| prop.class.generate(prop.length) }

    # Setting :format before passing on the initialization chain will cause
    # dm-validations (if present) to auto-add a format validation for us.
    # For some reason setting :length is not doing the same, so our format
    # validation here is technically validating both format and length.
    def initialize(model, name, options = {}, type = nil)
        options[:length] = options[:length]..options[:length] unless options[:length].is_a?(Range)
        options[:format] = /^[0-9a-z]{#{options[:length].min},#{options[:length].max}}$/ if defined? ::DataMapper::Validations
        model.send(:include, ::RetrySaveMixin)
        super
    end

    def primitive?(value)
        return value.kind_of?(::String)
    end

    # DM "core" validation (non dm-validations).  Validates both format and
    # length, but in the absence of dm-validations, the result will be #save
    # failure without actually populating #errors (confusing, but better
    # than saving bad data).
    def valid?(value, negated = false)
        super && value.match(/^[0-9a-z]{#{range.min},#{range.max}}$/)
    end

    def range
        return @length.is_a?(Range) ? @length : @length..@length
    end

    protected

    def self.generate(size)
        return Digest::SHA1.hexdigest(rand.to_s).to_i(16).to_s(36)[0..size-1]
    end
end

::DataMapper::Property::RefCode = ::RefCode

2_DM_retry_save_mixin.rb

module RetrySaveMixin
    MAX_SAVE_RETRIES = 5

    def regenerate_defaults
        self.send(:properties).select{ |p| p.default.is_a?(Proc) }.each do |prop|
            attribute_set(prop.name, prop.default.call(self, prop))
        end
    end

    def save_self(*args)
        return super unless new?
        retries = 0
        begin
            super
        rescue Exception => e
            raise if retries == MAX_SAVE_RETRIES
            regenerate_defaults
            retries += 1
            retry
        end
    end
end

3_example.rb

class Foo
    include ::DataMapper::Resource

    property :id, Serial
    property :ref_code, RefCode, :length => 8
end

::DataMapper.auto_migrate!

foo = Foo.create
bar = Foo.create(:ref_code => foo.ref_code)

# Tada!

Note that the "issue" with :length auto-validation goes away with: http://github.com/jpr5/dm-validations/commit/ea517f0bc85e04f77b61afa41c4ac6a0b0dd0e91. Pull request pending.