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     column although used in the query is not needed in the result set.
     In order to understand what the Relational DAS is doing when it builds 
     the data graph it may be helpful to visualise what the result set 
     looks like. Although the data in the database is normalised, so that 
     multiple department rows can point through their foreign key to one 
     company row, the data in the result set is non-normalised: that is, 
     if there is one company and multiple departments, the values for the 
     company are repeated in each row. The Relational DAS has to reverse 
     this process and turn the result set back into a normalised data graph, 
     with just one company object.
    </p></div>
    <div class="example-contents"><p>
     In this example the Relational DAS will examine the result set and 
     column specifier, find data for both the company and department 
     tables, find primary keys for both, and interpret each row as 
     containing data for a department and its parent company. If it has 
     not seen data for that company before (it uses the primary key to 
     check) it creates a company object and then a department object 
     underneath it. If it has seen data for that company before and 
     has already created the company object it just creates the 
     department object underneath.
    </p></div>

    <div class="example-contents"><p>
     In this way the Relational DAS can retrieve and renormalise data 
     for multiple companies and multiple departments underneath them.
    </p></div>

    <div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br /></span><span style="color: #007700">require_once&nbsp;</span><span style="color: #DD0000">'SDO/DAS/Relational.php'</span><span style="color: #007700">;<br />require_once&nbsp;</span><span style="color: #DD0000">'company_metadata.inc.php'</span><span style="color: #007700">;<br /><br /></span><span style="color: #FF8000">/**************************************************************<br />*&nbsp;Retrieve&nbsp;the&nbsp;company&nbsp;and&nbsp;Shoe&nbsp;department,&nbsp;then&nbsp;delete&nbsp;Shoe&nbsp;and&nbsp;add&nbsp;IT<br />***************************************************************/<br /></span><span style="color: #0000BB">$dbh&nbsp;</span><span style="color: #007700">=&nbsp;new&nbsp;</span><span style="color: #0000BB">PDO</span><span style="color: #007700">(</span><span style="color: #0000BB">PDO_DSN</span><span style="color: #007700">,</span><span style="color: #0000BB">DATABASE_USER</span><span style="color: #007700">,</span><span style="color: #0000BB">DATABASE_PASSWORD</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">$das&nbsp;</span><span style="color: #007700">=&nbsp;new&nbsp;</span><span style="color: #0000BB">SDO_DAS_Relational&nbsp;</span><span style="color: #007700">(</span><span style="color: #0000BB">$database_metadata</span><span style="color: #007700">,</span><span style="color: #DD0000">'company'</span><span style="color: #007700">,</span><span style="color: #0000BB">$SDO_containment_metadata</span><span style="color: #007700">);<br /><br /></span><span style="color: #0000BB">$root&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">$das</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">executeQuery</span><span style="color: #007700">(</span><span style="color: #0000BB">$dbh</span><span style="color: #007700">,<br /></span><span style="color: #DD0000">'select&nbsp;c.id,&nbsp;c.name,&nbsp;d.id,&nbsp;d.name&nbsp;from&nbsp;company&nbsp;c,&nbsp;department&nbsp;d&nbsp;where&nbsp;d.co_id&nbsp;=&nbsp;c.id'</span><span style="color: #007700">,<br />array(</span><span style="color: #DD0000">'company.id'</span><span style="color: #007700">,</span><span style="color: #DD0000">'company.name'</span><span style="color: #007700">,</span><span style="color: #DD0000">'department.id'</span><span style="color: #007700">,</span><span style="color: #DD0000">'department.name'</span><span style="color: #007700">));<br /><br /></span><span style="color: #0000BB">$acme&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">$root</span><span style="color: #007700">[</span><span style="color: #DD0000">'company'</span><span style="color: #007700">][</span><span style="color: #0000BB">0</span><span style="color: #007700">];&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="color: #FF8000">//&nbsp;get&nbsp;the&nbsp;first&nbsp;company&nbsp;-&nbsp;will&nbsp;be&nbsp;'Acme'<br /></span><span style="color: #0000BB">$shoe&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">$acme</span><span style="color: #007700">[</span><span style="color: #DD0000">'department'</span><span style="color: #007700">][</span><span style="color: #0000BB">0</span><span style="color: #007700">];&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="color: #FF8000">//&nbsp;get&nbsp;the&nbsp;first&nbsp;department&nbsp;underneath&nbsp;-&nbsp;will&nbsp;be&nbsp;'Shoe'<br /><br /></span><span style="color: #007700">unset(</span><span style="color: #0000BB">$acme</span><span style="color: #007700">[</span><span style="color: #DD0000">'department'</span><span style="color: #007700">][</span><span style="color: #0000BB">0</span><span style="color: #007700">]);<br /><br /></span><span style="color: #0000BB">$it&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">$acme</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">createDataObject</span><span style="color: #007700">(</span><span style="color: #DD0000">'department'</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">$it</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">name&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #DD0000">'IT'</span><span style="color: #007700">;<br /><br /></span><span style="color: #0000BB">$das&nbsp;</span><span style="color: #007700">-&gt;&nbsp;</span><span style="color: #0000BB">applyChanges</span><span style="color: #007700">(</span><span style="color: #0000BB">$dbh</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$root</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?&gt;</span>
</span>
</code></div>
    </div>

   </div>
  </p>

  <p class="para">
   <div class="example">
    <p><b>Example #3 One company, two departments - Retrieve and Delete</b></p>
    <div class="example-contents"><p>
     In this example the company and department are retrieved and 
     then deleted. It is not necessary to delete them individually 
     (although that would be possible) - deleting the company object 
     from the data graph also deletes any departments underneath it.
    </p></div>
    <div class="example-contents"><p>
     Note the way that the company object is actually deleted using the 
     PHP unset call. The unset has to be performed on the containing 
     property which in this case is 
     the company property on the special 
     root object. You must use:
     <div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br /></span><span style="color: #007700">unset(</span><span style="color: #0000BB">$root</span><span style="color: #007700">[</span><span style="color: #DD0000">'company'</span><span style="color: #007700">][</span><span style="color: #0000BB">0</span><span style="color: #007700">]);<br /></span><span style="color: #0000BB">?&gt;</span>
</span>
</code></div>
     </div>

     and not:
     <div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br /></span><span style="color: #007700">unset(</span><span style="color: #0000BB">$acme</span><span style="color: #007700">);&nbsp;</span><span style="color: #FF8000">//WRONG<br /></span><span style="color: #0000BB">?&gt;</span>
</span>
</code></div>
     </div>

     Simply unsetting
     <var class="varname">$acme</var>
     would destroy the variable but leave the data in the data 
     graph untouched.
    </p></div>

    <div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br /></span><span style="color: #007700">require_once&nbsp;</span><span style="color: #DD0000">'SDO/DAS/Relational.php'</span><span style="color: #007700">;<br />require_once&nbsp;</span><span style="color: #DD0000">'company_metadata.inc.php'</span><span style="color: #007700">;<br /><br /></span><span style="color: #FF8000">/**************************************************************<br />*&nbsp;Retrieve&nbsp;the&nbsp;company&nbsp;and&nbsp;IT&nbsp;department,&nbsp;then&nbsp;delete&nbsp;the&nbsp;whole&nbsp;company<br />***************************************************************/<br /></span><span style="color: #0000BB">$dbh&nbsp;</span><span style="color: #007700">=&nbsp;new&nbsp;</span><span style="color: #0000BB">PDO</span><span style="color: #007700">(</span><span style="color: #0000BB">PDO_DSN</span><span style="color: #007700">,</span><span style="color: #0000BB">DATABASE_USER</span><span style="color: #007700">,</span><span style="color: #0000BB">DATABASE_PASSWORD</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">$das&nbsp;</span><span style="color: #007700">=&nbsp;new&nbsp;</span><span style="color: #0000BB">SDO_DAS_Relational&nbsp;</span><span style="color: #007700">(</span><span style="color: #0000BB">$database_metadata</span><span style="color: #007700">,</span><span style="color: #DD0000">'company'</span><span style="color: #007700">,</span><span style="color: #0000BB">$SDO_containment_metadata</span><span style="color: #007700">);<br /><br /></span><span style="color: #0000BB">$root&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">$das</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">executeQuery</span><span style="color: #007700">(</span><span style="color: #0000BB">$dbh</span><span style="color: #007700">,<br /></span><span style="color: #DD0000">'select&nbsp;c.id,&nbsp;c.name,&nbsp;d.id,&nbsp;d.name&nbsp;from&nbsp;company&nbsp;c,&nbsp;department&nbsp;d&nbsp;where&nbsp;d.co_id&nbsp;=&nbsp;c.id'</span><span style="color: #007700">,<br />array(</span><span style="color: #DD0000">'company.id'</span><span style="color: #007700">,</span><span style="color: #DD0000">'company.name'</span><span style="color: #007700">,</span><span style="color: #DD0000">'department.id'</span><span style="color: #007700">,</span><span style="color: #DD0000">'department.name'</span><span style="color: #007700">));<br /><br /></span><span style="color: #0000BB">$acme&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">$root</span><span style="color: #007700">[</span><span style="color: #DD0000">'company'</span><span style="color: #007700">][</span><span style="color: #0000BB">0</span><span style="color: #007700">];<br /></span><span style="color: #0000BB">$it&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">$acme</span><span style="color: #007700">[</span><span style="color: #DD0000">'department'</span><span style="color: #007700">][</span><span style="color: #0000BB">0</span><span style="color: #007700">];<br /><br />unset(</span><span style="color: #0000BB">$root</span><span style="color: #007700">[</span><span style="color: #DD0000">'company'</span><span style="color: #007700">][</span><span style="color: #0000BB">0</span><span style="color: #007700">]);<br /><br /></span><span style="color: #0000BB">$das&nbsp;</span><span style="color: #007700">-&gt;&nbsp;</span><span style="color: #0000BB">applyChanges</span><span style="color: #007700">(</span><span style="color: #0000BB">$dbh</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$root</span><span style="color: #007700">);<br /><br /></span><span style="color: #0000BB">?&gt;</span>
</span>
</code></div>
    </div>

   </div>
  </p>
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