/en/reference/sdodasrel/examples.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision: 1.4 $ -->

<chapter xml:id="sdo.das.rel.examples" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
 &reftitle.examples;
 <section xml:id='sdo.das.rel.examples-crud'>
  <title>Creating, retrieving, updating and deleting data</title>
  <para>
   This section illustrates how the Relational DAS can be used to create, 
   retrieve, update and delete data in a relational database.
   Many of the examples are illustrated with a three-table database that 
   contains companies, departments within those companies, and employees 
   that work in those departments. This example is used in a number of 
   places within the SDO literature. See the examples section of the
   <link xlink:href='&url.ibm.sdo.spec;'>Service Data Objects specification</link>
   or the
   <link linkend="sdo.examples">Examples</link>
   section of the documentation for the SDO extension.
  </para>

  <para>
   The Relational DAS is constructed with metadata that defines the 
   relational database and how it should be mapped to SDO.
   The long section that follows describes this metadata and how to 
   construct the Relational DAS. The examples that follow it all assume that
   this metadata is in an included php file.
  </para>

  <para>
   The examples below and others can all be found in the
   <filename>Scenarios</filename>
   directory in the Relational DAS package.
  </para>

  <para>
   The Relational DAS throws exceptions in the event that it finds errors 
   in the metadata or errors when executing SQL statements against the 
   database. For brevity the examples below all omit the use of try/catch 
   blocks around the calls to the Relational DAS.
  </para>

  <para>
   These examples all differ from the expected use of SDO in two
   important respects.
  </para>
  <para>
   First, they show all interactions with the database completed within 
   one script. In this respect these scenarios are not realistic but are 
   chosen to illustrate just the use of the Relational DAS.
   It is expected that interactions with the database will be separated 
   in time and the data graph serialized and deserialized into the PHP 
   session one or more times as the application interacts with an end user.
  </para>
  <para>
   Second, all queries executed against the database use hard-coded 
   queries with no variables substituted. In this case it is safe to 
   use the simple 
   <function>executeQuery</function>
   call, and this is what the examples illustrate. 
   In practice, though, it is unlikely that the SQL statement is known 
   entirely ahead of time. In order to allow variables to be safely 
   substituted into the SQL queries, without running the risk of 
   injecting SQL with unknown effects, it is safer to use the 
   <function>executePreparedQuery</function>
   which takes a prepared SQL statement containing placeholders
   and a list of values to be substituted. 
  </para>
 </section>

 <section xml:id='sdo.das.rel.metadata'>
  <title>Specifying the metadata</title>
  <para>
   This first long section describes in detail how the metadata describing 
   the database and the required SDO model is supplied to the 
   Relational DAS.
  </para>
  <para>
   When the constructor for the Relational DAS is invoked, it needs to be 
   passed several pieces of information. The bulk of the information, 
   passed as an associative array in the first argument to the constructor, 
   tells the Relational DAS what it needs to know about the relational 
   database. It describes the names of the tables, columns, primary keys 
   and foreign keys. It should be fairly easy to understand what is 
   required, and once written it can be placed in a php file and included 
   when needed. The remainder of the information, passed in the second 
   and third arguments to the constructor, tells the Relational DAS what 
   it needs to know about the relationships between objects and the shape 
   of the data graph; it ultimately determines how the data from the 
   database is to be normalized into a graph.
  </para>

  <section xml:id='sdo.das.rel.metadata.database'>
   <title>Database metadata</title>
   <para>
    The first argument to the constructor describes the target 
    relational database.
   </para>

   <para>
    Each table is described by an associative array with up to four keys.
    <informaltable>
     <tgroup cols='2'>
      <thead>
       <row>
        <entry>Key</entry>
        <entry>Value</entry>
       </row>
      </thead>
      <tbody>
       <row>
        <entry>name</entry>
        <entry>The name of the table.</entry>
       </row>
       <row>
        <entry>columns</entry>
        <entry>
         An array listing the names of the columns, in any order.
        </entry>
       </row>
       <row>
        <entry>PK</entry>
        <entry>The name of the column containing the primary key.</entry>
       </row>
       <row>
        <entry>FK</entry>
        <entry>An array with two entries, 'from' and 'to', which define 
         a column containing a foreign key, and a table to which the foreign
         key points. If there are no foreign keys in the table then the 
         'FK' entry does not need to be specified. Only one foreign key 
         can be specified. Only a foreign key pointing to the primary key 
         of a table can be specified.
        </entry>
       </row>
      </tbody>
     </tgroup>
    </informaltable>
   </para>

   <programlisting role="php">
<![CDATA[
<?php
/*****************************************************************
* METADATA DEFINING THE DATABASE
******************************************************************/
$company_table = array (
  'name' => 'company',
  'columns' => array('id', 'name',  'employee_of_the_month'),
  'PK' => 'id',
  'FK' => array (
      'from' => 'employee_of_the_month',
      'to' => 'employee',
      ),
  );
$department_table = array (
  'name' => 'department', 
  'columns' => array('id', 'name', 'location', 'number', 'co_id'),
  'PK' => 'id',
  'FK' => array (
      'from' => 'co_id',
      'to' => 'company',
      )
  );
$employee_table = array (
  'name' => 'employee',
  'columns' => array('id', 'name', 'SN', 'manager', 'dept_id'),
  'PK' => 'id',
  'FK' => array (
      'from' => 'dept_id',
      'to' => 'department',
      )
  );
$database_metadata = array($company_table, $department_table, $employee_table);
?>
]]>
   </programlisting>

   <para>
    This metadata corresponds to a relational database that might have 
    been defined to MySQL as:
   </para>
   <programlisting role="sql">
<![CDATA[
create table company (
 id integer auto_increment,
 name char(20),
 employee_of_the_month integer,
 primary key(id)
);
create table department (
 id integer auto_increment,
 name char(20),
 location char(10),
 number integer(3),
 co_id integer,
 primary key(id)
);
create table employee (
 id integer auto_increment,
 name char(20),
 SN char(4),
 manager tinyint(1),
 dept_id integer,
 primary key(id)
);
]]>
   </programlisting>
   <para>
   or to DB2 as:
   </para>
   <programlisting role="sql">
<![CDATA[
create table company ( \
  id integer not null generated by default as identity,  \
  name varchar(20), \
  employee_of_the_month integer, \
  primary key(id) )
create table department ( \
  id integer not null generated by default as identity, \
  name varchar(20), \
  location varchar(10), \
  number integer, \
  co_id integer, \
  primary key(id) )
create table employee ( \
  id integer not null generated by default as identity, \
  name varchar(20), \
  SN char(4), \
  manager smallint, \
  dept_id integer, \
  primary key(id) )
]]>
   </programlisting>
   
   <para>
    Note that although in this example there are no foreign keys specified 
    to the database and so the database is not expected to enforce 
    referential integrity, the intention behind the
    <varname>co_id</varname>
    column on the department table and the
    <varname>dept_id</varname>
    column on the employee table is they should contain the primary key 
    of their containing company or department record, respectively.
    So these two columns are acting as foreign keys.
   </para>
                  
   <para>
    There is a third foreign key in this example, that from the
    <varname>employee_of_the_month</varname>
    column of the company record to a single row of the employee table.
    Note the difference in intent between this foreign key and the other 
    two. The
    <varname>employee_of_the_month</varname>
    column represents a single-valued relationship: there can be only 
    one employee of the month for a given company.
    The
    <varname>co_id</varname>
    and
    <varname>dept_id</varname>
    columns represent multi-valued relationships: a company can contain 
    many departments and a department can contain many employees.
    This distinction will become evident when the remainder of the metadata 
    picks out the company-department and department-employee relationships 
    as containment relationships.
   </para>

   <para>
    There are a few simple rules to be followed when constructing the 
    database metadata:
   </para>

   <itemizedlist>
    <listitem>
     <para>
      All tables must have primary keys, and the primary keys must be
      specified in the metadata. Without primary keys it is not possible 
      to keep track of object identities. As you can see from the SQL 
      statements that create the tables, primary keys can be 
      auto-generated, that is, generated and assigned by the database when
      a record is inserted. In this case the auto-generated primary key 
      is obtained from the database and inserted into the data object 
      immediately after the row is inserted into the database.
     </para>
    </listitem>

    <listitem>
     <para>
      It is not necessary to specify in the metadata all the columns 
      that exist in the database, only those that will be used. 
      For example, if the company table had another column that the 
      application did not want to access with SDO, this need not be 
      specified in the metadata. On the other hand it would have done 
      no harm to specify it: if specified in the metadata but never 
      retrieved, or assigned to by the application, then the unused column 
      will not affect anything.
     </para>
    </listitem>

    <listitem>
     <para>
      In the database metadata note that the foreign key definitions 
      identify not the destination column in the table which is pointed 
      to, but the table name itself. Strictly, the relational model 
      permits the destination of a foreign key to be a non-primary key.
      Only foreign keys that point to a primary key are useful for 
      constructing the SDO model, so the metadata specifies the table name.
      It is understood that the foreign key points to the primary key of 
      the given table.
     </para>
    </listitem>
   </itemizedlist>

   <para>
    Given these rules, and given the SQL statements that define the 
    database, the database metadata should be easy to construct.
   </para>

   <section xml:id='sdo.das.rel.metadata.database.model'>
    <title>What the Relational DAS does with the metadata</title>
    <para>
     The Relational DAS uses the database metadata to form most of the 
     SDO model. For each table in the database metadata, an SDO type 
     is defined. Each column which can represent a primitive value 
     (columns which are not defined as foreign keys) are added 
     as properties to the SDO type.
    </para>
    <para>
     All primitive properties are given a type of string in the SDO model, 
     regardless of their SQL type. When writing values back to the 
     database the Relational DAS will create SQL statements that treat 
     the values as strings, and the database will convert them to the 
     appropriate type.
    </para>

    <para>
     Foreign keys are interpreted in one of two ways, depending on the 
     metadata in the third argument to the constructor that defines
     the SDO containment relationships.
     A discussion of this is therefore deferred until the section on
     <link linkend="sdo.das.rel.metadata.crels">
      SDO containment relationships
     </link>
     below.
    </para>
   </section>

   <section xml:id='sdo.das.rel.metadata.approottype'>
    <title>Specifying the application root type</title>
    <para>
     The second argument to the constructor is the application root type.
     The true root of each data graph is an object of a special root type 
     and all application data objects come somewhere below that. Of the 
     various application types in the SDO model, one has to be the 
     application type immediately below the root of the data graph.
     If there is only one table in the database metadata, the application 
     root type can be inferred, and this argument can be omitted.
    </para>
   </section>

   <section xml:id='sdo.das.rel.metadata.crels'>
    <title>Specifying the SDO containment relationships</title>

    <para>
     The third argument to the constructor defines how the types in the 
     model are to be linked together to form a graph. It identifies the 
     parent-child relationships between the types which collectively form a 
     graph. The relationships need to be supported by foreign keys to be 
     found in the data, in a way shortly to be described.
    </para>

    <para>
     The metadata is an array containing one or more associative arrays, 
     each of which identifies a parent and a child. The example below shows 
     a parent-child relationship from company to department, and another 
     from department to employee. Each of these will become an SDO property 
     defining a multi-valued containment relationship in the SDO model.

    </para>
    <programlisting role="php">
<![CDATA[
<?php
$department_containment = array( 'parent' => 'company', 'child' => 'department');
$employee_containment = array( 'parent' => 'department', 'child' => 'employee');

$SDO_containment_metadata = array($department_containment, $employee_containment);           
?>
]]>
    </programlisting>

    <para>
     Foreign keys in the database metadata are interpreted as properties 
     with either multi-valued containment relationships or single-valued 
     non-containment references, depending on whether they have a 
     corresponding SDO containment relationship specified in the metadata. 
     In the example here, the foreign keys from department to company (the 
     <varname>co_id</varname>
     column in the department table)
     and from employee to department (the
     <varname>dept_id</varname>
     column in the employee table) are interpreted as supporting the
     SDO containment relationships.
     Each containment relationship mentioned in the SDO containment relationships
     metadata must have a corresponding foreign key present in the
     database and defined in the database metadata. The values of the 
     foreign key columns for containment relationships do not appear in the 
     data objects, instead each is represented by a containment relationship 
     from the parent to the child. So the
     <varname>co_id</varname>
     column in the department row in the database, for example, does not 
     appear as a property on the department type, but instead as a 
     containment relationship called
     <varname>department</varname>
     on the company type.
     Note that the foreign key and the parent-child relationship appear to 
     have opposite senses: the foreign key points from the department to 
     the company, but the parent-child relationship points from company to 
     department.
    </para>

    <para>
     The third foreign key in this example, the
     <varname>employee_of_the_month</varname>
     ,
     is handled differently.
     This is not mentioned in the SDO containment relationships metadata.
     As a consequence this is interpreted in the second way: it becomes 
     a single-valued non-containment reference on the company object, to
     which can be assigned references to SDO data objects of the employee 
     type. It does appear as a property on the company type. The way to 
     assign a value to it in the SDO data graph is to have a graph that 
     contains an employee object through the containment relationships, and 
     to assign the object to it. This is illustrated in the later examples 
     below.
    </para>
   </section>
  </section> <!--specifying the metadata sdo.das.rel.metadata.database.model -->
 </section> <!-- sdo.das.rel.metadata -->

 <section xml:id='sdo.das.rel.examples.one-table'>
  <title>One-table examples</title>
  <para>
   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.
  </para>

  <para>
   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.
  </para>

  <para>
   <example>
    <title>Creating a data object</title>
    <para>
     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
     <link linkend="sdo.examples">Examples</link>
     section on the SDO extension for other ways of accessing the 
     properties of an object.
    </para>

    <para>
     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
     <function>createDataObject</function>
     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'.
    </para>
    <para>
     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.
    </para>
                      
    <programlisting role="php" xml:id="sdo.das.rel.examples.1c-C">
<![CDATA[
<?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);
?>
]]>
    </programlisting>
   </example>
  </para>

  <para>
   <example>
    <title>Retrieving a data object</title>
    <para>
     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
     <varname>name</varname>
     and
     <varname>id</varname>
     properties are echoed.
    </para>
    <para>
     In this example the third argument to
     <function>executeQuery</function>,
     the column specifier is needed as there are other tables in the 
     metadata with column names of
     <varname>name</varname>
     and
     <varname>id</varname>.
     If there were no possible ambiguity it could be omitted.
    </para>
    <programlisting role="php" xml:id="sdo.das.rel.examples.1c-R">
<![CDATA[
<?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";
}
?>
]]>
    </programlisting>
   </example>
  </para>

  <para>
   <example>
    <title>Updating a data object</title>
    <para>
     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.
    </para>
    <para>
     In this example the same instance of the Relational DAS is reused 
     for the
     <function>applyChanges</function>,
     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.
    </para>
    <programlisting role="php" xml:id="sdo.das.rel.examples.1c-RU">
<![CDATA[
<?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);
?>
]]>
    </programlisting>
   </example>
  </para>

  <para>
   <example>
    <title>Deleting a data object</title>
    <para>
     Any companies called 'Acme' or its reverse 'emcA' are retrieved.
     They are then all deleted from the graph with unset.
    </para>

    <para>
     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.
    </para>
    <programlisting role="php" xml:id="sdo.das.rel.examples.1c-RD">
<![CDATA[
<?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);
?>
]]>
    </programlisting>
   </example>
  </para>

 </section> <!-- one-table -->

 <section xml:id='sdo.das.rel.examples.two-table'>
  <title>Two-table examples</title>
  <para>
   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.
  </para>
  <para>
   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.
  </para>
  <para>
   You can find these examples combined into one script called
   <filename>1cd-CRUD</filename>
   in the
   <filename>Scenarios</filename>
   directory in the Relational DAS package.
  </para>

  <para>
   <example>
    <title>One company, one department - Create</title>
    <para>
     As in the earlier example of creating just one company data object, 
     the first action after constructing the Relational DAS is to call
     <function>createRootDataObject</function>
     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.
    </para>
    <para>
     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 
     <varname>id</varname>
     in the company table and the
     <varname>co_id</varname>
     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
     <function>getLastInsertId</function>
     method to obtain the auto-generated primary key, then add that as 
     the value of the
     <varname>co_id</varname>
     column when inserting the department row.
    </para>
    <programlisting role="php" xml:id="sdo.das.rel.examples.1cd-C">
<![CDATA[
<?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);

?>
]]>
    </programlisting>
   </example>
  </para>

  <para>
   <example>
    <title>One company, one department - Retrieve and Update</title>

    <para>
     In this case the SQL query passed to
     <function>executeQuery</function>
     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 
     <function>executeQuery</function>
     call enabling the Relational DAS to know which column is which in 
     the result set.
    </para>
    <para>
     Note that the
     <varname>co_id</varname>
     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.
    </para>
    <para>
     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.
    </para>

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

    <programlisting role="php" xml:id="sdo.das.rel.examples.1cd-RU">
<![CDATA[
<?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);
?>
]]>
    </programlisting>
   </example>
  </para>

  <para>
   <example>
    <title>One company, two departments - Retrieve and Delete</title>
    <para>
     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.
    </para>
    <para>
     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:
     <programlisting role="php" xml:id="sdo.das.rel.examples.1cd-CRUD.good-delete">
<![CDATA[
<?php
unset($root['company'][0]);
?>
]]>
     </programlisting>
     and not:
     <programlisting role="php" xml:id="sdo.das.rel.examples.1cd-CRUD.bad-delete">
<![CDATA[
<?php
unset($acme); //WRONG
?>
]]>
     </programlisting>
     Simply unsetting
     <varname>$acme</varname>
     would destroy the variable but leave the data in the data 
     graph untouched.
    </para>

    <programlisting role="php" xml:id="sdo.das.rel.examples.1cd-RD">
<![CDATA[
<?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);

?>
]]>
    </programlisting>
   </example>
  </para>
 </section>

 <section xml:id='sdo.das.rel.examples.three-table'>
  <title>Three-table example</title>
  <para>
   The following examples use all three tables from the company database: 
   the company, department, and employee tables. These introduce the final 
   piece of function not exercised by the examples above: the 
   non-containment reference
   <varname>employee_of_the_month</varname>.
  </para>
  <para>
   Like the examples above for company and department, this set of examples 
   is intended to illustrate the full lifecycle of such a data graph.
  </para>


  <para>
   <example>
    <title>One company, one department, one employee - Create</title>
    <para>
     In this example a company is created containing one department and 
     just one employee. Note that this example clears out all three tables 
     at the start so that the exact results of the queries can be known.
    </para>
    <para>
     Note how once the company, department and employee have been created, 
     the
     <varname>employee_of_the_month</varname>
     property of the company can be made to point at the new employee.
     As this is a non-containment reference, this cannot be done until 
     the employee object has been created within the graph.
     Non-containment references need to be managed carefully.
     For example if the employee were now deleted from under the department, 
     it would not be correct to try to save the graph without
     first clearing or re-assigning the
     <varname>employee_of_the_month</varname>
     property.
     The closure rule for SDO data graphs requires that any object pointed 
     at by a non-containment reference must also be reachable by 
     containment relationships.
    </para>
    <para>
     When it comes to inserting the graph into the database, the procedure 
     is similar to the example of inserting the company and department,
     but
     <varname>employee_of_the_month</varname>
     introduces an extra complexity.
     The Relational DAS needs to insert the objects working down the tree 
     formed by containment relationships, so company, then department, then 
     employee. This is necessary so that it always has the auto-generated 
     primary key of a parent on hand to include in a child row. But when 
     the company row is inserted the employee who is employee of the month 
     has not yet been inserted and the primary key is not known. The 
     procedure is that after the employee record is inserted and its 
     primary key known, a final step is performed in which the the 
     company record is updated with the employee's primary key.
    </para>
    <programlisting role="php" xml:id="sdo.das.rel.examples.1cde-C">
<![CDATA[
<?php
require_once 'SDO/DAS/Relational.php';
require_once 'company_metadata.inc.php';

/*************************************************************************************
* Empty out the three 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();
$pdo_stmt = $dbh->prepare('DELETE FROM EMPLOYEE;');
$rows_affected = $pdo_stmt->execute();

/*************************************************************************************
* Create a tiny but complete company.
* The company name is Acme.
* There is one department, Shoe.
* There is one employee, Sue.
* The employee of the month is Sue.
*************************************************************************************/
$das = new SDO_DAS_Relational ($database_metadata,'company',$SDO_containment_metadata);
$dbh = new PDO(PDO_DSN,DATABASE_USER,DATABASE_PASSWORD);

$root             = $das  -> createRootDataObject();
$acme             = $root -> createDataObject('company');
$acme -> name     = "Acme";
$shoe             = $acme -> createDataObject('department');
$shoe -> name     = 'Shoe';
$shoe -> location = 'A-block';
$sue              = $shoe -> createDataObject('employee');
$sue -> name      = 'Sue';
$acme -> employee_of_the_month = $sue;

$das -> applyChanges($dbh, $root);

echo "Wrote back Acme with one department and one employee\n";
?>
]]>
    </programlisting>
   </example>
  </para>

  <para>
   <example>
    <title>One company, one department, one employee - Retrieve and update</title>
    <para>
     The SQL statement passed to the Relational DAS is this time an inner 
     join that retrieves data from all three tables. Otherwise this example 
     introduces nothing that has not appeared in a previous example. 
    </para>
    <para>
     The graph is updated by the addition of a new department and employee 
     and some alterations to the name properties of the existing objects 
     in the graph. The combined changes are then written back. The 
     Relational DAS will process and apply an arbitrary mixture of 
     additions, modifications and deletions to and from the data graph.
    </para>
    <programlisting role="php" xml:id="sdo.das.rel.examples.1cde-RU">
<![CDATA[
<?php
require_once 'SDO/DAS/Relational.php';
require_once 'company_metadata.inc.php';

/*************************************************************************************
* Find the company again and change various aspects.
* Change the name of the company, department and employee.
* Add a second department and a new employee.
* Change the employee of the month.
*************************************************************************************/
$das = new SDO_DAS_Relational ($database_metadata,'company',$SDO_containment_metadata);
$dbh = new PDO(PDO_DSN,DATABASE_USER,DATABASE_PASSWORD);

$root = $das->executeQuery($dbh,
  "select c.id, c.name, c.employee_of_the_month, d.id, d.name, e.id, e.name " .
  "from company c, department d, employee e " .
  "where e.dept_id = d.id and d.co_id = c.id and c.name='Acme'",
   array('company.id','company.name','company.employee_of_the_month',
   'department.id','department.name','employee.id','employee.name'));
$acme         = $root['company'][0];

$shoe         = $acme->department[0];
$sue          = $shoe -> employee[0];

$it           = $acme->createDataObject('department');
$it->name     = 'IT';
$it->location = 'G-block';
$billy        = $it->createDataObject('employee');
$billy->name  = 'Billy';

$acme->name   = 'MegaCorp';
$shoe->name   = 'Footwear';
$sue->name    = 'Susan';

$acme->employee_of_the_month = $billy;
$das -> applyChanges($dbh, $root);
echo "Wrote back company with extra department and employee and all the names changed (Megacorp/Footwear/Susan)\n";

?>
]]>
    </programlisting>
   </example>
  </para>

  <para>
   <example>
    <title>One company, two departments, two employees - Retrieve and delete</title>
    <para>
     The company is retrieved as a complete data graph containing five 
     data objects - the company, two departments and two employees.
     They are all deleted by deleting the company object. Deleting an 
     object from the graph deletes all the object beneath it in the graph.
     Five SQL DELETE statements will be generated and  executed. As always 
     they will be qualified with a WHERE clause that contains all of the 
     fields that were retrieved, so that any updates to the data in the 
     database in the meantime by another process will be detected.
    </para>
    <programlisting role="php" xml:id="sdo.das.rel.examples.1cde-RD">
<![CDATA[
<?php
require_once 'SDO/DAS/Relational.php';
require_once 'company_metadata.inc.php';

/*************************************************************************************
* Now read it one more time and delete it.
* You can delete part, apply the changes, then carry on working with the same graph but
* care is needed to keep closure - you cannot delete the employee who is eotm without
* reassigning. For safety here we delete the company all in one go. 
*************************************************************************************/
$das = new SDO_DAS_Relational ($database_metadata,'company',$SDO_containment_metadata);
$dbh = new PDO(PDO_DSN,DATABASE_USER,DATABASE_PASSWORD);

$root = $das->executeQuery($dbh,
  "select c.id, c.name, c.employee_of_the_month, d.id, d.name, e.id, e.name " .
  "from company c, department d, employee e " .
  "where e.dept_id = d.id and d.co_id = c.id and c.name='MegaCorp';",
   array('company.id','company.name','company.employee_of_the_month',
   'department.id','department.name','employee.id','employee.name'));
$megacorp = $root['company'][0];

unset($root['company']);
$das -> applyChanges($dbh, $root);

echo "Deleted the company, departments and employees all in one go.\n";

?>
]]>
    </programlisting>
   </example>
  </para>
 </section>
</chapter>

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