Creating, retrieving, updating and deleting
data

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 » Service Data Objects specification
or the Examples
section of the documentation for the SDO extension.

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.

The examples below and others can all be found in
the Scenarios directory in the
Relational DAS package.

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.

These examples all differ from the expected use of
SDO in two important respects.

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.

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 executeQuery() 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 executePreparedQuery() which
takes a prepared SQL statement containing placeholders and a list
of values to be substituted.