MongoMapper STI?

[koops]

Has anyone tried to do ActiveRecord-style single-table inheritance
with MongoMapper? Is there a clean way to do it?

The best solution I've come up with is to have a type column and use
it to dynamically include an appropriate module on method_missing.

[David James]

Have you considered using embedded documents instead? This might solve your problem right away and more elegantly.

--
David James
Web Developer at Sunlight Labs
dja...@sunlightfoundation.com
AIM: davidatsunlight
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[koops]

Embedded documents work for data, not behavior, so I don't see how
that could solve my problem. I'd like MongoMapper to instantiate an
different class based on a type parameter.

[David Cuadrado]

it's already implemented, for example:

class Base
  include MongoMapper::Document
  key :shared                 

  before_create { |d| d[:_type] = d.class.name }
end

class Child1 < Base
  key :a
end

class Child2 < Base
  key :b
end

Child1.create(:a => 1)
Child2.create(:b => 2)

Base.all.each { |e| puts e.inspect }

--
David Cuadrado

[John Nunemaker]

Yep. You don't need the before_create as MM handles that for you. 

[koops]

That's excellent. Does it work for embedded documents too?

[John Nunemaker]

Yeah. I think so.

[koops]

Doesn't seem to work for me:

require 'rubygems'
require 'mongo_mapper'

MongoMapper.database = 'test'

class Embed
include MongoMapper::EmbeddedDocument
end

class Embed1 < Embed
end

class Embed2 < Embed
end

class Doc
include MongoMapper::Document
key :embed, Embed
end

Doc.create(:embed => Embed1.new)
Doc.create(:embed => Embed2.new)
p Doc.all

[John Nunemaker]

You have to define _type key in your embed model.

[koops]

Sorry to say that didn't work, nor did setting the _type in the embed
document manually. It's always instantiated as the base class.

[John Nunemaker]

Ah right now only polymorphic many embedded docs properly handle this.
I'll look into it.

[Jim Mulholland]

This may have been mentioned somewhere else in the past week, but STI
is working great for us on Mongo_Mapper 0.5.8.

Very slick stuff!

[jnunemaker]

This is now fixed in master and should be released in gem soon.

[mepatterson]

Maybe I'm confused on how this is supposed to work --

class Animal
include MongoMapper::Document
end

class Dog < Animal
end

class Cat < Animal
end

5.times { Dog.create }
4.times { Cat.create }

>> Dog.count
=> 9

>> Cat.count
=> 9

shouldn't those counts reflect the counts of the actual type of
object, not the count of the base object?

[mepatterson]

Ahh, okay. I have to manually define

key :_type, String

on my Animal model. That seems to work fine now.