Working with multiple database interfaces: improving the "DBIGenerator" class - PHP

So far, we've seen the significant limitations of the original class in real applications. Certainly, we need to develop a more flexible class that will be capable of generating multiple DB interfaces, in order to work with several database tables. Therefore, the brand new "DBIGenerator" class might be defined like this:

class DBIGenerator{

var $table;

var $name;

var $path;

function DBIGenerator
($table,$name='default_file.php',$path='DEFAULTPATH/'){

$this->table=$table;

$this->name=$name;

$this->path=$path;

}

function generate(){

// build class header

$str='<?php class '.$this->name.'{';

if(!$result=mysql_query("SHOW COLUMNS FROM $this->table")){

die('Could not run query '.mysql_error());

}

// build data member declaration

if(mysql_num_rows($result)>0){

while($row=mysql_fetch_array($result,MYSQL_ASSOC)){

$str.='var $'.$row['Field'].'=\'\';';

$methods.='function set'.$row['Field'].'($'.$row['Field'].')
{$this->'.$row['Field'].'=$'.$row['Field'].';}';

$methods.='function get'.$row['Field'].'(){return $this-
>'.$row['Field'].';}';

// store field names in array

$fields[]=$row['Field'];

}

}

// build empty constructor

$str.='function '.$this->name.'(){}';

// build modifiers and accesors

$str.=$methods;

unset($methods);

// build load() method

$str.='function load(){$r=mysql_query("SELECT * FROM
'.$this->table.' WHERE id=\'$this->id\'");';

$str.='return mysql_fetch_array($r,MYSQL_ASSOC);}';

// build submit() method

$str.='function submit(){mysql_query("INSERT INTO '.$this-
>table.' SET ';

foreach($fields as $field){

$str.=($field!='id')?$field.'=\'$this->'.$field.'\',':'';

}

$str.='");$this->id=mysql_insert_id();';

$str=preg_replace("/,\"/","\"",$str).'}';

// build update() method

$str.='function update(){mysql_query("UPDATE '.$this-
>table.' SET ';

foreach($fields as $field){

$str.=($field!='id')?$field.'=\'$this->'.$field.'\',':'';

}

$str=preg_replace("/,$/","",$str);

$str.=' WHERE id=\'$this->id\'");}';

// build delete() method

$str.='function delete(){mysql_query("DELETE FROM '.$this-
>table.' WHERE id=\'$this->id\'");}';

$str.='}?>';

// write class code to file

$fp=fopen($this->path.$this->name.'.php','w') or die('Failed
opening file');

fwrite($fp,$str);

fclose($fp);

// delete temporary variables

unset($fp,$str,$row,$fields,$field);

}

function getObject(){

// check if class file exists

if(file_exists($this->path.$this->name.'.php')){

require_once($this->path.$this->name.'.php');

// create object

return new $this->name;

}

return false;

}

}

Despite the fact that the source class code is quite long, its simplicity is remarkable. Taking a closer look at it, we can see that its logic is fairly similar to the previous version. Jumping straight into its code, the constructor takes three incoming parameters, described as follows: the first one $table represents the database table from which the database interface will be created. This single parameter implies a big improvement compared to the previous version, since it allows to rapidly generate a DB interface from any table passed to the class.

The second parameter $name, means the file name of the DB interface class to be created. Finally the third argument, $path, indicates the path within the file system where the class will be physically located. The constructor simply assigns these values as class properties, as we see below:

function DBIGenerator
($table,$name='default_file.php',$path='DEFAULTPATH/'){

$this->table=$table;

$this->name=$name;

$this->path=$path;

}

Again, I've specified default values for the name of the DB interface class, as well as for the path. As you can see, the constructor definition is closely similar to the old version.

The next thing to do is to explain the logic of the "generate()" method, which obviously takes charge of generating the DB interface class file, including the required methods to set up the access points to a given database table. Join me in the next section to learn how this is done.