[PATCH] Discriminator type demodulize feature request

[datamapper]

[PATCH] Discriminator type demodulize feature request

[solnic]

The patch at http://github.com/dmgr/dm-core/commit/58017d02987e9fdbae23750c3ab1079f47b3e5c5 looks good as it will allow to implement your specific needs in dm-types which probably is a better place then dm-core, like you said on IRC.

by Martin Gamsjaeger (snusnu)

[solnic]

I created a repo with my custom discriminator types:
http://github.com/dmgr/dmg-types

In the future they can be moved to dm-types if core developers want it.

They will work if you will merge my commit, I prefer this one:
http://github.com/dmgr/dm-core/commit/6af8cab37dfeb7aa1b0230399fddf239e6aac590

by Dawid Marcin Grzesiak

[solnic]

The commit: http://github.com/dmgr/dm-core/commit/83fba6abcf8bdb2e41371c3d20e78a26950c54dc
will let you do something like this:

require ’rubygems’
require ’datamapper’

DataMapper.setup(:default, "sqlite3::memory:")

class Car
  include DataMapper::Resource

  property :id, Serial
  @brand = property :brand, String
  @name = property :name, String

  class Ford < self
    class Torino < self
    end
  end

  class Audi < self
    class TT < self
    end
  end

  def self.discrimination(record)
    case record[@brand]
      when "Audi" then if &rsquo;TT&rsquo; == record[@name]
          Audi::TT
        else
          Audi
        end
      when "Ford" then if &rsquo;Torino&rsquo; == record[@name]
          Ford::Torino
        else
          Ford
        end
      else self
    end
  end
end

p Car.new(:brand => &rsquo;Opel&rsquo;, :name => &rsquo;Astra&rsquo;)  #<Car @id=nil @brand="Opel" @name="Astra">
p Car.new(:brand => &rsquo;Ford&rsquo;, :name => &rsquo;K&rsquo;)      #<Car::Ford @id=nil @brand="Ford" @name="K">
p Car.new(:brand => &rsquo;Ford&rsquo;, :name => &rsquo;Torino&rsquo;) #<Car::Ford::Torino @id=nil @brand="Ford" @name="Torino">
p Car.new(:brand => &rsquo;Audi&rsquo;, :name => &rsquo;TT&rsquo;)     #<Car::Audi::TT @id=nil @brand="Audi" @name="TT">

Additionally default scopes need to be updated in derived classes.

by Dawid Marcin Grzesiak

[solnic]

Because I need this behavior in my project I had to implement it on v0.10.2 so the solution I use is there:
http://github.com/dmgr/dm-core/tree/my0.10.2

and the code for master branch which I provided before:
http://github.com/dmgr/dm-core
is not the actual one.

by Dawid Marcin Grzesiak

[solnic]

Yeah, I generally like to hold onto adding new features into the core until there is at least a few people asking for them. Even then I think new features should be put into plugins, and stabilized there. Once it gets enough usage we can talk about moving it into the core.

I would suggest packaging this up into a plugin, and then seeing if there is any interest on the DataMapper mailing list.

by Dan Kubb (dkubb)