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    <p>For the first question about the schema and adding items autonomously you might consider using <code>dm-is-tree</code> for your <code>Deviceclass</code> it'll do a lot of the work for you. Below is an example of creating an item and 'later on' adding associated items.</p> <pre><code>require 'rubygems' require 'data_mapper' require 'dm-is-tree' # setup DataMapper::Logger.new($stdout, :debug) DataMapper.setup(:default, 'sqlite::memory:') # models class Deviceclass include DataMapper::Resource property :id, Serial property :hw_id, String, :unique =&gt; true property :name, String property :updated_at, DateTime property :created_at, DateTime is :tree, :order =&gt; :name has n, :devices end class Device include DataMapper::Resource property :id, Serial property :device_class_id, Integer property :name, String property :updated_at, DateTime property :created_at, DateTime belongs_to :deviceclass, :required =&gt; false end # go! DataMapper.finalize DataMapper.auto_upgrade! # make the root deviceclass parent = Deviceclass.create(:name =&gt; "Root") # later on make a child child = Deviceclass.create(:name =&gt; "Child") # and add it to the parent parent.children &lt;&lt; child # again later, create some devices d1 = Device.create(:name =&gt; "D1") d2 = Device.create(:name =&gt; "D2") # add them parent.devices &lt;&lt; d1 child.devices &lt;&lt; d2 # get stuffs puts parent.children puts child.root puts parent.devices puts child.devices </code></pre> <p>I'm not sure it's a good idea to use validation to generate missing Deviceclasses. If the initial data is not constantly changing I'd run a seed script on startup. You can use something like <a href="https://github.com/datamapper/dm-sweatshop" rel="nofollow">dm-sweatshop</a> to seed the db.</p> <p>I think I need a few more details on #3 do you want a default name for a Deviceclass (you can add <code>:default =&gt; 'foo'</code>) which you might know as you are using <code>:default</code> already! :)</p>
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    1. CONice! I'll check into the dm-is-tree and dm-sweatshop modules. Thanks for those pointers! As for #3 what I'm basically trying to accomplish is inserting default records into a table for which the :default will be derived from one of those records for the property :parent_deviceclass_id. Any additional thoughts on that front?
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