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POIn Ruby, with ActiveRecord what is the best way to retrieve an object that belongs_to a parent object, given some conditions?
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  1. POIn Ruby, with ActiveRecord what is the best way to retrieve an object that belongs_to a parent object, given some conditions?
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    copied!<p>In my model an <code>Organisation</code> <code>has_many :users</code>, and a <code>User</code> <code>has_and_belongs_to_many :roles</code> and a <code>Role</code> has a <code>name</code> and <code>has_and_belongs_to_many :users</code>.</p> <p>In my <code>Organisation</code> class I have a method <code>get_admin</code> that is supposed to get the <code>User</code> belonging to that <code>Organisation</code> who has the <code>Role</code> <code>'admin'</code>. Like so:</p> <pre><code>def get_admin return self.users.with_role('admin') end </code></pre> <p>Alas this returns an <code>ActiveRecord::Relation</code> object, not a <code>User</code>.</p> <p>I tried appending <code>.first</code> to the end of the line like so</p> <pre><code>def get_admin return self.users.with_role('admin').first end </code></pre> <p>But then all I get is an SQL error</p> <pre><code>ActiveRecord::StatementInvalid: SQLite3::SQLException: no such column: role.name: SELECT "users".* FROM "users" WHERE ("users".organisation_id = 2) AND (role.name == 'admin') LIMIT 1 </code></pre> <p>My schema is defined thusly:</p> <pre><code>create_table "roles", :force =&gt; true do |t| t.string "name", :null =&gt; false end create_table "users", :force =&gt; true do |t| t.string "username", :null =&gt; false t.integer "organisation_id" end create_table "roles_users", :id =&gt; false, :force =&gt; true do |t| t.integer "user_id" t.integer "role_id" end create_table "organisations", :force =&gt; true do |t| t.string "name", :null =&gt; false t.string "website", :null =&gt; false end </code></pre> <p>How would I rewrite the <code>Organisation</code>'s <code>get_admin</code> method (as follows) to return an actual <code>User</code>?</p> <pre><code>def get_admin return self.users.with_role('admin') end </code></pre> <p>Cheers</p> <p>Dave</p>
 

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