One-table examples
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## Two-table examples

The following set of examples all use two tables from the company database: the company and department tables. These examples exercise more of the function of the Relational DAS.

In this series of examples a company and department are created, retrieved, updated, and finally deleted. This illustrates the lifecycle for a data graph containing more than one object. Note that this example clears out the company and department tables at the start so that the exact results of the queries can be known.

You can find these examples combined into one script called 1cd-CRUD in the Scenarios directory in the Relational DAS package.

Example #1 One company, one department - Create

As in the earlier example of creating just one company data object, the first action after constructing the Relational DAS is to call createRootDataObject() to obtain the special root object of the otherwise empty data graph. The company object is then created as a child of the root object, and the department object as a child of the company object.

When it comes to applying the changes, the Relational DAS has to perform special processing to maintain the foreign keys that support the containment relationships, especially if auto-generated primary keys are involved. In this example, the relationship between the auto-generated primary key id in the company table and the co_id column in the department table must be maintained. When inserting a company and department for the first time the Relational DAS has to first insert the company row, then call PDO's getLastInsertId() method to obtain the auto-generated primary key, then add that as the value of the co_id column when inserting the department row.

`<?php
require_once 'SDO/DAS/Relational.php';
require_once 'company_metadata.inc.php';
/*************************************************************************************
* Empty out the two tables
*************************************************************************************/
$dbh = new PDO(PDO_DSN,DATABASE_USER,DATABASE_PASSWORD);
$pdo_stmt = $dbh->prepare('DELETE FROM COMPANY;');
$rows_affected = $pdo_stmt->execute();
$pdo_stmt = $dbh->prepare('DELETE FROM DEPARTMENT;');
$rows_affected = $pdo_stmt->execute();
/**************************************************************
* Create a company with name Acme and one department, the Shoe department
***************************************************************/
$dbh = new PDO(PDO_DSN,DATABASE_USER,DATABASE_PASSWORD);
$das = new SDO_DAS_Relational ($database_metadata,'company',$SDO_containment_metadata);
$root = $das -> createRootDataObject();
$acme = $root -> createDataObject('company');
$acme -> name = "Acme";
$shoe = $acme->createDataObject('department');
$shoe->name = 'Shoe';
$das -> applyChanges($dbh, $root);
?>`

Example #2 One company, one department - Retrieve and Update

In this case the SQL query passed to executeQuery() performs an inner join to join the data from the company and department tables. Primary keys for both the company and department tables must be included in the query. The result set is re-normalised to form a normalised data graph. Note that a column specifier is passed as the third argument to the executeQuery() call enabling the Relational DAS to know which column is which in the result set.

Note that the co_id 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.

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.

In this way the Relational DAS can retrieve and renormalise data for multiple companies and multiple departments underneath them.

`<?php
require_once 'SDO/DAS/Relational.php';
require_once 'company_metadata.inc.php';
/**************************************************************
* Retrieve the company and Shoe department, then delete Shoe and add IT
***************************************************************/
$dbh = new PDO(PDO_DSN,DATABASE_USER,DATABASE_PASSWORD);
$das = new SDO_DAS_Relational ($database_metadata,'company',$SDO_containment_metadata);
$root = $das->executeQuery($dbh,
'select c.id, c.name, d.id, d.name from company c, department d where d.co_id = c.id',
array('company.id','company.name','department.id','department.name'));
$acme = $root['company'][0]; // get the first company - will be 'Acme'
$shoe = $acme['department'][0]; // get the first department underneath - will be 'Shoe'
unset($acme['department'][0]);
$it = $acme->createDataObject('department');
$it->name = 'IT';
$das -> applyChanges($dbh, $root);
?>`

Example #3 One company, two departments - Retrieve and Delete

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.

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:

`<?php
unset($root['company'][0]);
?>`

and not:

`<?php
unset($acme); //WRONG
?>`

Simply unsetting $acme would destroy the variable but leave the data in the data graph untouched.

`<?php
require_once 'SDO/DAS/Relational.php';
require_once 'company_metadata.inc.php';
/**************************************************************
* Retrieve the company and IT department, then delete the whole company
***************************************************************/
$dbh = new PDO(PDO_DSN,DATABASE_USER,DATABASE_PASSWORD);
$das = new SDO_DAS_Relational ($database_metadata,'company',$SDO_containment_metadata);
$root = $das->executeQuery($dbh,
'select c.id, c.name, d.id, d.name from company c, department d where d.co_id = c.id',
array('company.id','company.name','department.id','department.name'));
$acme = $root['company'][0];
$it = $acme['department'][0];
unset($root['company'][0]);
$das -> applyChanges($dbh, $root);
?>`

One-table examples
Three-table example
Ejemplos
PHP Manual