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POSetting up Associations with DataMapper & Sinatra
 

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    <p>Ok, so this is driving me crazy. I have read the Associations article and example and been trying to work this out for the las three days and I'm tired of this making me feel dumb, so... </p> <p>How does one set up associations with DataMapper? </p> <p>(I am using DM with Sinatra with SQLite3. Everything word fine for single tables with multiple values etc. It's when I start to try to associate them that I start getting errors.) </p> <p>Let's say I have an Orchard full of Apple Trees. Each Tree has many Apples. Each Apple has many Seeds. Therefore each tree has many Seeds through its Apples</p> <pre><code>require 'sinatra' require 'datamapper' DataMapper::setup(:default, "sqlite3://#{Dir.pwd}/orchard.db") # Trees in the orchard. class Tree include DataMapper::Resource property :id, Serial has n, :apples has n, :seeds, :through =&gt; :apples end # Apples on a Tree. class Apple include DataMapper::Resource property :id, Serial belongs_to :tree belongs_to :seed end # Seeds in an Apple class Seed include DataMapper::Resource property :id, Serial has n, :apple has n, :tree, :through =&gt; apple end DataMapper.finalize.auto_upgrade! </code></pre> <p>Is that correct? I keep getting various errors when I try to run this. Mostly along the lines of invalid association or cannot create column NULL with value NULL etc. What am I not understanding about this relationship?</p> <p>Further, Once I have a working model how do I go about getting information from it?</p> <p>If there are 3 trees:</p> <pre><code>Tree.all.count =&gt; 3 </code></pre> <p>If there are 2 apples:</p> <pre><code>Apple.all =&gt;[#&lt;Apple @id=1&gt;, #&lt;Apple @id=2&gt;] </code></pre> <p>Ok cool. But how many Apples does Tree #2 have? How many Seeds does Tree #4 have? How many Apples in total? How many Seeds in total?</p> <p>Any help would be greatly appreciated. </p>
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