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<h1 class="header">GroupedScope</h1>
<p class="header">Has Many Associations IN (GROUPS)</p>

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<p class="header">This project is maintained by <a class="header name" href="https://github.com/metaskills">metaskills</a></p>


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<section>
<h1>Has Many Associations IN (GROUPS)</h1>

<p><img src="http://metaskills.net/assets/jack.png" alt="Jack Has Many Things" width="320" height="214"></p>

<p>GroupedScope provides an easy way to group objects and to allow those groups to share association collections via existing <code>has_many</code> relationships. You may enjoy my original article titled <a href="http://metaskills.net/2008/09/28/jack-has_many-things/"><em>Jack has_many :things</em></a>.</p>

<h2>Installation</h2>

<p>Install the gem with bundler. We follow a semantic versioning format that tracks ActiveRecord's minor version. So this means to use the latest 3.2.x version of GroupedScope with any ActiveRecord 3.2 version.</p>

<div class="highlight"><pre><span class="n">gem</span> <span class="s1">'grouped_scope'</span><span class="p">,</span> <span class="s1">'~&gt; 3.2.0'</span>
</pre></div>

<h2>Setup</h2>

<p>To use GroupedScope on a model it must have a <code>:group_id</code> column.</p>

<div class="highlight"><pre><span class="k">class</span> <span class="nc">AddGroupId</span> <span class="o">&lt;</span> <span class="no">ActiveRecord</span><span class="o">::</span><span class="no">Migration</span>
<span class="k">def</span> <span class="nf">up</span>
<span class="n">add_column</span> <span class="ss">:employees</span><span class="p">,</span> <span class="ss">:group_id</span><span class="p">,</span> <span class="ss">:integer</span>
<span class="k">end</span>
<span class="k">def</span> <span class="nf">down</span>
<span class="n">remove_column</span> <span class="ss">:employees</span><span class="p">,</span> <span class="ss">:group_id</span>
<span class="k">end</span>
<span class="k">end</span>
</pre></div>

<h2>General Usage</h2>

<p>Assume the following model.</p>

<div class="highlight"><pre><span class="k">class</span> <span class="nc">Employee</span> <span class="o">&lt;</span> <span class="no">ActiveRecord</span><span class="o">::</span><span class="no">Base</span>
<span class="n">has_many</span> <span class="ss">:reports</span>
<span class="n">grouped_scope</span> <span class="ss">:reports</span>
<span class="k">end</span>
</pre></div>

<p>By calling grouped_scope on any association you create a new group accessor for each
instance. The object returned will act just like an array and at least include the
current object that called it.</p>

<div class="highlight"><pre><span class="vi">@employee_one</span><span class="o">.</span><span class="n">group</span> <span class="c1"># =&gt; [#&lt;Employee id: 1, group_id: nil&gt;]</span>
</pre></div>

<p>To group resources, just assign the same <code>:group_id</code> to each record in that group.</p>

<div class="highlight"><pre><span class="vi">@employee_one</span><span class="o">.</span><span class="n">update_attribute</span> <span class="ss">:group_id</span><span class="p">,</span> <span class="mi">1</span>
<span class="vi">@employee_two</span><span class="o">.</span><span class="n">update_attribute</span> <span class="ss">:group_id</span><span class="p">,</span> <span class="mi">1</span>
<span class="vi">@employee_one</span><span class="o">.</span><span class="n">group</span> <span class="c1"># =&gt; [#&lt;Employee id: 1, group_id: 1&gt;, #&lt;Employee id: 2, group_id: 1&gt;]</span>
</pre></div>

<p>Calling grouped_scope on the :reports association leaves the existing association intact.</p>

<div class="highlight"><pre><span class="vi">@employee_one</span><span class="o">.</span><span class="n">reports</span> <span class="c1"># =&gt; [#&lt;Report id: 2, employee_id: 1&gt;]</span>
<span class="vi">@employee_two</span><span class="o">.</span><span class="n">reports</span> <span class="c1"># =&gt; [#&lt;Report id: 18, employee_id: 2&gt;, #&lt;Report id: 36, employee_id: 2&gt;]</span>
</pre></div>

<p>Now the good part, all associations passed to the grouped_scope method can be called
on the group proxy. The collection will return resources shared by the group.</p>

<div class="highlight"><pre><span class="vi">@employee_one</span><span class="o">.</span><span class="n">group</span><span class="o">.</span><span class="n">reports</span> <span class="c1"># =&gt; [#&lt;Report id: 2, employee_id: 1&gt;, </span>
<span class="c1">#&lt;Report id: 18, employee_id: 2&gt;, </span>
<span class="c1">#&lt;Report id: 36, employee_id: 2&gt;]</span>
</pre></div>

<p>You can even call scopes or association extensions defined on the objects in the collection
defined on the original association. For instance:</p>

<div class="highlight"><pre><span class="vi">@employee</span><span class="o">.</span><span class="n">group</span><span class="o">.</span><span class="n">reports</span><span class="o">.</span><span class="n">urgent</span><span class="o">.</span><span class="n">assigned_to</span><span class="p">(</span><span class="n">user</span><span class="p">)</span>
</pre></div>

<h2>Advanced Usage</h2>

<p>The group scoped object can respond to either <code>blank?</code> or <code>present?</code> which checks the group's
target <code>group_id</code> presence or not. We use this internally so that grouped scopes only use grouping
SQL when absolutely needed.</p>

<div class="highlight"><pre><span class="vi">@employee_one</span> <span class="o">=</span> <span class="no">Employee</span><span class="o">.</span><span class="n">create</span> <span class="ss">:group_id</span> <span class="o">=&gt;</span> <span class="kp">nil</span>
<span class="vi">@employee_two</span> <span class="o">=</span> <span class="no">Employee</span><span class="o">.</span><span class="n">create</span> <span class="ss">:group_id</span> <span class="o">=&gt;</span> <span class="mi">38</span>

<span class="vi">@employee_one</span><span class="o">.</span><span class="n">group</span><span class="o">.</span><span class="n">blank?</span> <span class="c1"># =&gt; true</span>
<span class="vi">@employee_two</span><span class="o">.</span><span class="n">group</span><span class="o">.</span><span class="n">present?</span> <span class="c1"># =&gt; true</span>
</pre></div>

<p>The object returned by the <code>#group</code> method is an ActiveRecord relation on the targets class,
in this case <code>Employee</code>. Given this, you can further scope the grouped proxy if needed. Below,
we use the <code>:email_present</code> scope to refine the group down.</p>

<div class="highlight"><pre><span class="k">class</span> <span class="nc">Employee</span> <span class="o">&lt;</span> <span class="no">ActiveRecord</span><span class="o">::</span><span class="no">Base</span>
<span class="n">has_many</span> <span class="ss">:reports</span>
<span class="n">grouped_scope</span> <span class="ss">:reports</span>
<span class="n">scope</span> <span class="ss">:email_present</span><span class="p">,</span> <span class="n">where</span><span class="p">(</span><span class="s2">"email IS NOT NULL"</span><span class="p">)</span>
<span class="k">end</span>

<span class="vi">@employee_one</span> <span class="o">=</span> <span class="no">Employee</span><span class="o">.</span><span class="n">create</span> <span class="ss">:group_id</span> <span class="o">=&gt;</span> <span class="mi">5</span><span class="p">,</span> <span class="ss">:name</span> <span class="o">=&gt;</span> <span class="s1">'Ken'</span>
<span class="vi">@employee_two</span> <span class="o">=</span> <span class="no">Employee</span><span class="o">.</span><span class="n">create</span> <span class="ss">:group_id</span> <span class="o">=&gt;</span> <span class="mi">5</span><span class="p">,</span> <span class="ss">:name</span> <span class="o">=&gt;</span> <span class="s1">'MetaSkills'</span><span class="p">,</span> <span class="ss">:email</span> <span class="o">=&gt;</span> <span class="s1">'ken@metaskills.net'</span>

<span class="c1"># Only one employee is returned now.</span>
<span class="vi">@employee_one</span><span class="o">.</span><span class="n">group</span><span class="o">.</span><span class="n">email_present</span> <span class="c1"># =&gt; [#&lt;Employee id: 1, group_id: 5, name: 'MetaSkills', email: 'ken@metaskills.net']</span>
</pre></div>

<p>We always use raw SQL to get the group ids vs. mapping them to an array and using those in scopes.
This means that large groups can avoid pushing down hundreds of keys in SQL form. So given an employee
with a <code>group_id</code> of <code>43</code> and calling <code>@employee.group.reports</code>, you would get something similar to
the following SQL.</p>

<div class="highlight"><pre><span class="k">SELECT</span> <span class="ss">"reports"</span><span class="p">.</span><span class="o">*</span>
<span class="k">FROM</span> <span class="ss">"reports"</span>
<span class="k">WHERE</span> <span class="ss">"reports"</span><span class="p">.</span><span class="ss">"employee_id"</span> <span class="k">IN</span> <span class="p">(</span>
<span class="k">SELECT</span> <span class="ss">"employees"</span><span class="p">.</span><span class="ss">"id"</span>
<span class="k">FROM</span> <span class="ss">"employees"</span>
<span class="k">WHERE</span> <span class="ss">"employees"</span><span class="p">.</span><span class="ss">"group_id"</span> <span class="o">=</span> <span class="mi">43</span>
<span class="p">)</span>
</pre></div>

<p>You can pass the group scoped object as a predicate to ActiveRecord's relation interface. In past
versions, this would have treated the group object as an array of IDs. The new behavior is to return
a SQL literal to be used with IN statements. So note, the following would generate SQL similar to
the one above.</p>

<div class="highlight"><pre><span class="no">Employee</span><span class="o">.</span><span class="n">where</span><span class="p">(</span><span class="ss">:group_id</span> <span class="o">=&gt;</span> <span class="vi">@employee</span><span class="o">.</span><span class="n">group</span><span class="p">)</span><span class="o">.</span><span class="n">all</span>
</pre></div>

<p>If you need more control and you are working with the group at a lower level, you can always
use the <code>#ids</code> or <code>#ids_sql</code> methods on the group.</p>

<div class="highlight"><pre><span class="c1"># Returns primary key array.</span>
<span class="vi">@employee</span><span class="o">.</span><span class="n">group</span><span class="o">.</span><span class="n">ids</span> <span class="c1"># =&gt; [33, 58, 240]</span>

<span class="c1"># Returns a Arel::Nodes::SqlLiteral object.</span>
<span class="vi">@employee</span><span class="o">.</span><span class="n">group</span><span class="o">.</span><span class="n">ids_sql</span> <span class="c1"># =&gt; 'SELECT "employees"."id" FROM "employees" WHERE "employees"."group_id" = 33'</span>
</pre></div>

<h2>Todo List</h2>

<ul>
<li>Raise errors for :finder_sql/:counter_sql.</li>
<li>Add a user definable group_id schema.</li>
<li>Remove SelfGrouping#with_relation, has not yet proved useful.</li>
</ul><h2>Testing</h2>

<p>Simple! Just clone the repo, then run <code>bundle install</code> and <code>bundle exec rake</code>. The tests will begin to run. We also use Travis CI to run our tests too. Current build status is:</p>

<p><a href="http://travis-ci.org/metaskills/grouped_scope"><img src="https://secure.travis-ci.org/metaskills/grouped_scope.png" alt="Build Status"></a></p>

<h2>License</h2>

<p>Released under the MIT license.
Copyright (c) 2011 Ken Collins</p>
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