| Re: database access [message #174202 is a reply to message #174199] |
Thu, 26 May 2011 15:41   |
Jerry Stuckle
Messages: 2598
Registered: September 2010
Karma:
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Senior Member |
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On 5/26/2011 10:22 AM, sheldonlg wrote:
> On 5/26/2011 9:00 AM, Jerry Stuckle wrote:
>> On 5/26/2011 8:09 AM, sheldonlg wrote:
>>> On 5/25/2011 5:37 PM, Jerry Stuckle wrote:
>>>> On 5/25/2011 1:17 PM, Jivanmukta wrote:
>>>> > I new relatively new to PHP. I need your opinion if the following set
>>>> > of database functions make sense:
>>>> >
>>>> > function openDatabase() {
>>>> > global $db;
>>>> > try {
>>>> > $db = new PDO('mysql:host=' . MYSQL_SERVER . ';dbname=' .
>>>> > MYSQL_DATABASE, MYSQL_USER, MYSQL_PASSWORD);
>>>> > $db->exec('SET NAMES latin2');
>>>> > $db->exec('SET CHARACTER SET latin2 COLLATE latin2_general_ci');
>>>> > $db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
>>>> > register_shutdown_function('closeDatabase');
>>>> > } catch (PDOException $e) {
>>>> > return false;
>>>> > }
>>>> > return true;
>>>> > }
>>>> >
>>>> > function closeDatabase() {
>>>> > global $db, $inTransaction;
>>>> > if ($inTransaction) {
>>>> > $db->rollBack();
>>>> > $inTransaction = false;
>>>> > }
>>>> > if (!is_null($db)) {
>>>> > $db = null;
>>>> > }
>>>> > }
>>>> >
>>>> > function queryDatabase($sql) {
>>>> > global $db, $inTransaction;
>>>> > $result = array();
>>>> > try {
>>>> > $qry = $db->query($sql);
>>>> > if (!empty($qry)) {
>>>> > $result = $qry->fetchAll();
>>>> > }
>>>> > } catch (PDOException $e) {
>>>> > if ($inTransaction) {
>>>> > $db->rollBack();
>>>> > }
>>>> > error(ERRMSG_DATABASE_OPERATION_FAILED);
>>>> > }
>>>> > return $result;
>>>> > }
>>>> >
>>>> > function execDatabase($sql) {
>>>> > global $db, $inTransaction;
>>>> > $result = array();
>>>> > try {
>>>> > $result = $db->exec($sql);
>>>> > } catch (PDOException $e) {
>>>> > if ($inTransaction) {
>>>> > $db->rollBack();
>>>> > }
>>>> > error(ERRMSG_DATABASE_OPERATION_FAILED);
>>>> > }
>>>> > return $result;
>>>> > }
>>>> >
>>>> > function startTransaction() {
>>>> > global $db, $inTransaction;
>>>> > $db->beginTransaction();
>>>> > $inTransaction = true;
>>>> > }
>>>> >
>>>> > function commitTransaction() {
>>>> > global $db, $inTransaction;
>>>> > $inTransaction = false;
>>>> > if ($db->commit()) {
>>>> > return;
>>>> > }
>>>> > $db->rollBack();
>>>> > error(ERRMSG_DATABASE_OPERATION_FAILED);
>>>> > }
>>>> >
>>>> > function rollbackTransaction() {
>>>> > global $db, $inTransaction;
>>>> > $inTransaction = false;
>>>> > if ($db->rollBack()) {
>>>> > return;
>>>> > }
>>>> > error(ERRMSG_DATABASE_OPERATION_FAILED);
>>>> > }
>>>> >
>>>> > function lockTables($tables) {
>>>> > return execDatabase('LOCK TABLES ' . join(' WRITE, ', $tables) . '
>>>> > WRITE');
>>>> > }
>>>> >
>>>> > function unlockTables() {
>>>> > return execDatabase('UNLOCK TABLES');
>>>> > }
>>>>
>>>> Kind of, and maybe a bit overkill. But personally I'd put it all in a
>>>> Database class. The code would be more flexible and less prone to
>>>> errors.
>>>>
>>>
>>> Further, I would not have globals. I would pass $db in via the
>>> constructor. Likewise, I would have $inTransaction be a class variable
>>> which gets set by the method startTransaction().
>>>
>>
>> That was part of the class, Sheldon. In fact, I wouldn't even pass $db
>> into the constructor; it (along with $inTransaction, as you note) would
>> be class variables. That way the rest of the program is completely
>> independent of the database (and you can have more than one database
>> active concurrently if you want).
>
> If you don't pass it in with the constructor, then you need something
> like a setDb($parameter) to set the class variable. Passing it along
> with the constructor does not limit you to only one database
> concurrently. After all, you could readily do
>
> $dbObj1 = new DatabaseClass($db1);
> $dbObj2 = new DatabaseClass($db2);
>
> What passing it along inside the constructor does is (a) it saves a line
> of code each time in the invocation process(es) and (b) uniquely
> identifies a particular instance of the class. Since the DatabaseClass
> _MUST_ have the db defined, there is no problem with passing it in with
> the constructor and no reason not to do so.
>
A better way would be to pass the basic information to the constructor -
i.e. the host, userid, password and database name. Let the constructor
build the database object. That way it is completely encapsulated and
the rest of the program is not dependent on a database object. If he
later finds he wants to change database objects (i.e. maybe PDO is to
slow and he wants to use mysqli), he can do so without changing anything
in the rest of the program. The class is now more fully encapsulated.
A very good reason for not passing it to the constructor.
--
==================
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstucklex(at)attglobal(dot)net
==================
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