One-table examples
The following set of examples all use the Relational DAS to work with a data graph containing just one application data object, a single company and the data just to be found the company table. These examples do not exercise the power of SDO or the Relational DAS and of course the same result could be achieved more economically with direct SQL statements but they are intended to illustrate how to work with the Relational DAS.
For this very simple scenario it would be possible to simplify the database metadata to include just the company table - if that were done the second and third arguments to the constructor and the column specifier used in the query example would become optional.
Example #1 Creating a data object
The simplest example is that of creating a single data object and writing it to the database. In this example a single company object is created, its name is set to 'Acme', and the Relational DAS is called to write the changes to the database. The company name is set here using the property name method. See the Examples section on the SDO extension for other ways of accessing the properties of an object.
Data objects can only be created when you have a data object to start with, however. It is for that reason that the first call to the Relational DAS here is to obtain a root object. This is in effect how to ask for an empty data graph - the special root object is the true root of the tree. The company data object is then created with a call to createDataObject() on the root object. This creates the company data object and inserts it in the graph by inserting into a multi-valued containment property on the root object called 'company'.
When the Relational DAS is called to apply the changes a simple insert statement 'INSERT INTO company (name) VALUES ("Acme");' will be constructed and executed. The auto-generated primary key will be set into the data object and the change summary will be reset, so that it would be possible to continue working with the same data object, modify it, and apply the newer changes a second time.
<?php
require_once 'SDO/DAS/Relational.php';
require_once 'company_metadata.inc.php';
/**************************************************************
* Construct the DAS with the metadata
***************************************************************/
$das = new SDO_DAS_Relational ($database_metadata,'company',$SDO_containment_metadata);
/**************************************************************
* Obtain a root object and create a company object underneath.
* Make a simple change to the data object.
***************************************************************/
$root = $das -> createRootDataObject();
$acme = $root -> createDataObject('company');
$acme->name = "Acme";
/**************************************************************
* Get a database connection and write the object to the database
***************************************************************/
$dbh = new PDO(PDO_DSN,DATABASE_USER,DATABASE_PASSWORD);
$das -> applyChanges($dbh, $root);
?>
Example #2 Retrieving a data object
In this example a single data object is retrieved from the database - or possibly more than one if there is more than one company called 'Acme'. For each company returned, the name and id properties are echoed.
In this example the third argument to executeQuery(), the column specifier is needed as there are other tables in the metadata with column names of name and id. If there were no possible ambiguity it could be omitted.
<?php
require_once 'SDO/DAS/Relational.php';
require_once 'company_metadata.inc.php';
/**************************************************************
* Construct the DAS with the metadata
***************************************************************/
$das = new SDO_DAS_Relational ($database_metadata,'company',$SDO_containment_metadata);
/**************************************************************
* Get a database connection
***************************************************************/
$dbh = new PDO(PDO_DSN,DATABASE_USER,DATABASE_PASSWORD);
/**************************************************************
* Issue a query to obtain a company object - possibly more if they exist
***************************************************************/
$root = $das->executeQuery($dbh,
'select name, id from company where name="Acme"',
array('company.name', 'company.id') );
/**************************************************************
* Echo name and id
***************************************************************/
foreach ($root['company'] as $company) {
echo "Company obtained from the database has name = " .
$company['name'] . " and id " . $company['id'] . "\n";
}
?>
Example #3 Updating a data object
This example combines the previous two, in the sense that in order to be updated the object must first be retrieved. The application code reverses the company name (so 'Acme' becomes 'emcA') and then the changes are written back to the database in the same way that they were when the object was created. Because the query searches for the name both ways round the program can be run repeatedly to find the company and reverse its name each time.
In this example the same instance of the Relational DAS is reused for the applyChanges(), as is the PDO database handle. This is quite alright; it also alright to allow the previous instances to be garbage collected and to obtain new instances. No state data regarding the graph is held the Relational DAS once it has returned a data graph to the application. All necessary data is either within the graph itself, or can be reconstructed from the metadata.
<?php
require_once 'SDO/DAS/Relational.php';
require_once 'company_metadata.inc.php';
/**************************************************************
* Construct the DAS with the metadata
***************************************************************/
$das = new SDO_DAS_Relational ($database_metadata,'company',$SDO_containment_metadata);
/**************************************************************
* Get a database connection
***************************************************************/
$dbh = new PDO(PDO_DSN,DATABASE_USER,DATABASE_PASSWORD);
/**************************************************************
* Issue a query to obtain a company object - possibly more if they exist
***************************************************************/
$root = $das->executeQuery($dbh,
'select name, id from company where name="Acme" or name="emcA"',
array('company.name', 'company.id') );
/**************************************************************
* Alter the name of just the first company
***************************************************************/
$company = $root['company'][0];
echo "obtained a company with name of " . $company->name . "\n";
$company->name = strrev($company->name);
/**************************************************************
* Write the change back
***************************************************************/
$das->applyChanges($dbh,$root);
?>
Example #4 Deleting a data object
Any companies called 'Acme' or its reverse 'emcA' are retrieved. They are then all deleted from the graph with unset.
In this example they are all deleted in one go by unsetting the containing property (the property defining the containment relationship). It is also possible to delete them individually.
<?php
require_once 'SDO/DAS/Relational.php';
require_once 'company_metadata.inc.php';
/**************************************************************
* Construct the DAS with the metadata
***************************************************************/
$das = new SDO_DAS_Relational ($database_metadata,'company',$SDO_containment_metadata);
/**************************************************************
* Get a database connection
***************************************************************/
$dbh = new PDO(PDO_DSN,DATABASE_USER,DATABASE_PASSWORD);
/**************************************************************
* Issue a query to obtain a company object - possibly more if they exist
***************************************************************/
$root = $das->executeQuery($dbh,
'select name, id from company where name="Acme" or name="emcA"',
array('company.name', 'company.id') );
/**************************************************************
* Delete any companies found from the data graph
***************************************************************/
unset($root['company']);
/**************************************************************
* Write the change(s) back
***************************************************************/
$das->applyChanges($dbh,$root);
?>
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Document created the 30/01/2003, last modified the 26/10/2018
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References
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