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Extract

(PHP 3>= 3.0.7, PHP 4 , PHP 5)

extract -- Import variables into the current symbol table from an array

Description

int extract ( array var_array [, int extract_type [, string prefix]])

This function is used to import variables from an array into the current symbol table. It takes an associative array, var_array, and treats keys as variable names and values as variable values. For each key/value pair, it will create a variable in the current symbol table, subject to the extract_type and prefix parameters.

Note: Beginning with version 4.0.5, this function returns the number of variables extracted.

Note: EXTR_IF_EXISTS and EXTR_PREFIX_IF_EXISTS were introduced in version 4.2.0.

       Note: EXTR_REFS was introduced in version 4.3.0.

extract() checks each key to see whether it has a valid variable name. It also checks for collisions with existing variables in the symbol table. The way invalid/numeric keys and collisions are treated is determined by the extract_type. It can be one of the following values:

  • extr_overwrite - If there is a collision, overwrite the existing variable.

  • extr_skip - If there is a collision, do not overwrite the existing variable.

  • extr_prefix_same  - If there is a collision, prefix the variable name with prefix.

  • extr_prefix_all  - Prefix all variable names with prefix. Beginning with PHP 4.0.5, this includes numeric variables as well.

  •  extr_prefix_invalid  - Only prefix invalid/numeric variable names with prefix. This flag was added in PHP 4.0.5.

  • extr_if_exists - Only overwrite the variable if it already exists in the current symbol table, otherwise do nothing. This is useful for defining a list of valid variables and then extracting only those variables that are defined out of $_REQUEST, for example. This flag was added in PHP 4.2.0.

  •  extr_prefix_if_exists - Only create prefixed variable names if the non-prefixed version of the same variable exists in the current symbol table. This flag was added in PHP 4.2.0.

  • extr_refs - Extracts variables as references; this effectively means that the values of the imported variables are still referencing the values of the var_array parameter. Use this flag on its own or combine it with any other flag by OR’ing the extract_type. This flag was added in PHP 4.3.0.

If extract_type is not specified, it is assumed to be extr_overwrite. Note that prefix is only required if extract_type is EXTR_PREFIX_SAME, extr_prefix_all, extr_prefix_invalidor extr_prefix_if_exists.

If the prefixed result is not a valid variable name, it is not imported into the symbol table. extract() returns the number of variables successfully imported into the symbol table.

Extract functions can be used to extract variables from global arrays like $_SESSION or $_POST into program variables, thus achieving almost the same effect as with the register_globals configuration directive. Of course, the negative consequences are also the same. Collisions with existing variables can and will occur. This function is to be used with extreme caution, if ever. Debugging scripts with problems like this can be extremely painful. 

The last question that needs to be answered before the next example is “what can be put into the $_SESSION array”?

The answer is anything, provided the type is defined before executing the session_start() function. Object types like OCI_Session are ideal for sharing via session mechanism. The object and all of its members are shared automatically, without having to put each member into the $_SESSION array.

The last request does somewhat limit the usefulness of the __autoload() function and requires each class description be loaded by an explicit include, not waiting for PHP to load it when a new object is created.

It is now possible to rework example 13, and do something useful with the newly created database connection. Login form and the OCI_Session will remain the same; the only part that needs changing is the example13.php script itself:

Example 13a

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2//EN">
<html>
<head>
  <title>Example 13a</title>
</head>
<body>
  <?php
            require_once('OCI_Session.php');
            require('login_form.php');   
            session_start();
            if (!isset($_POST['user'])) {
                             login_form('SCOTT');
            }
            else {
               try { $dbh=new OCI_Session($_POST['user'],
                                          $_POST['passwd'],
                                          $_POST['database']);
    if (isset($dbh->err))
        throw new exception($dbh->err['message']);
    else {       
          $_SESSION['dbh']=$dbh;                     
          header('Location: query1.php');
    }
}
     catch (exception $e) {
     ?>
    <center>
    <?php
          echo "Exception:".$e->getMessage();
          login_form($_POST['user']);
    ?>
    <br>
    </center>
    <?php } }?>
</body>
</html>


The important changes are related to the session and marked by the bold font. Note that session_start() was called after including the OCI_Session and that the __autoload
() function was not used.  The next thing to note is the use of the header() function to redirect browser to another URL. In this case it was just “query1.php” which is a short form for:

http://localhost/work/query1.php  

This is another PHP script on the local machine. It is preferable to type the full URL because it will work the same way, regardless of the server and virtual directory configuration.  Header function sends the argument as a part of HTTP header to the browser. This is a little trick to “redirect” the client browser to another script.

The goal of this section was to demonstrate sharing of data between sessions. To do that, another script named query1.php is needed:

Example 13a (Cont)

<html>
<head>
<title>Query1</title>
</head>
<body>
<?php
require_once('OCI_Session.php');
session_start();
$dbh=$_SESSION['dbh'];
$SQL="select e.ename,e.empno,d.dname,d.loc,e.sal
            from emp e, dept d
            where e.deptno=d.deptno
            order by e.deptno,ename";
try {
      $dbh->refresh();
      if (!$dbh->db) {
         $e=$dbh->err;
         throw new Exception ('CONN:'.$e['message']);
      }
      $sth=oci_parse($dbh->db,$SQL);
      if (!$sth) {
         $e=oci_error($sth);
         throw new Exception ('PARSE:'.$e['message']);
      }
      if (!oci_execute($sth)) {
         $e=oci_error($sth);
         throw new Exception ('EXEC:'.$e['message']);
      }
      ?>
      <center>
      <table>
      <tr align="left"
          valign="middle"
          style="background-color: #ADD8E6; ">
       <td>ENAME     </td>
       <th>EMPNO     </th>
       <th>DPT. NAME </th>
       <th>LOCATION  </th>
       <th>SALARY    </th>
        </tr>
      <?php
      while ($row=oci_fetch_array($sth)) {
      ?>
        <tr>
          <td> <?=$row[0]?> </td>
          <td> <?=$row[1]?> </td>
          <td> <?=$row[2]?> </td>
          <td> <?=$row[3]?> </td>
          <td> <?=$row[4]?> </td>
        </tr>
      <?php
      }
      ?>
      </table>
      </center>
      <?php
    }
catch (Exception $e) {
       print $e->getMessage();
}
               

?>
</body>
<html>

What does this script do? This script starts a session and reads all session variables. There is only one, the variable $dbh. It is a database handle, shared with the login form drawn by the example13a.php

It is important to note that refresh() is being called on the handle. Remember from the beginning of the chapter, the refresh() method  of the OCI_Session class re-establishes the database connection.

Why re-connect to the database? This is not the same request as the one that handled the login form, so it may be handled by a different process.  The entities that connect to databases are processes, not “pages” or browsers. Thus, it must be assumed that this new process is not connected to the database. This means the user must re-connect. This is the primary purpose of the refresh() member of the OCI_Session class.

As a general rule, one must assume the process handling the request is not connected to the database and that it needs to. The $dbh handle contains username, password and the destination database, so that is not a problem.

Furthermore, functions such as oci_parse, oci_execute and oci_fetch_array are seen. These functions are well known to anybody who has ever worked with Oracle.  The most basic function is oci_parse(), which parses a SQL statement and creates a “cursor”. Cursors are Oracle handles for SQL statements.

The next function in the lot is oci_execute() which executes the parsed SQL statement. One function that deserves mention (OCI8 will be explained in detail in the next chapter) is oci_fetch_array(). It returns an array, which can be addressed both as a hash using column names and as a regular array using column numbers. This feature is extremely useful. 

The missing function that is not seen in this script is inserting. This function “binds” PHP variable to a SQL variable.  This makes it possible to use a PHP variable to formulate a WHERE condition like the following:

    SELECT ename,deptno, mgr,hiredate
    FROM    emp
    WHERE  empno = :EMPNO

The “bind” function makes it possible to substitute a PHP variable instead of the SQL placeholder “:EMPNO”. This also applies to the PL/SQL procedures and their arguments. The purpose of bind is to avoid multiple parse calls as these are getting increasingly expensive with the advent of the cost based optimizer.  Utilizing binds also makes HTML forms more secure and prevents common tricks like SQL injection.

The script output is shown below:

This is the expected result of a query operating on the two very well known Oracle demo tables.  One last thing to point out in this chapter is the use of HTML tables. The way HTML table is used here is typical. It is convenient to display query results as HTML table. All formatting is done by browser which knows how to format HTML. Later in this book it will be demonstrated through the use of PEAR even more convenient methods for displaying tables.


See code depot for complete scripts


The above book excerpt is from:

Easy Oracle PHP

Create Dynamic Web Pages with Oracle Data

ISBN 0-9761573-0-6   

Mladen Gogala

http://www.rampant-books.com/book_2005_2_php_oracle.htm

 

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