PDO Question - Call to a member function query() on a non-object

[peterv3]

I've been using PHP for a while, but I'm just starting to try PDO. I'm trying to create a handle in an include file that connects to the database, but I get this error:

[COLOR="Red"][B]( ! ) Fatal error: Call to a member function query() on a non-object in /Users/peterv/Sites/lp2/INCLUDES/process_books.php on line 31[/B][/COLOR]

process_switch.php: This calls the pdo_dbc function in the dbcp.php file, then calls the process_books.php script that incurs the error:

<?php
// Updated: Thursday March 24, 2011 - 1:40 PM
//Connect to PROJECT1 database.
[B][COLOR="Red"] require_once('./INCLUDES/dbcp.php');
  $dbh = pdo_dbc();[/COLOR][/B] 
//
// Determine processing by screenid.
  $screenid = $_POST['screenid'];
//  $formoption: search, add, etc.
  $formoption=$_POST['formoption'];
  $title=$_POST['title'];
//
  switch ($screenid) {
  case 'authors_form1.php':
       include('./INCLUDES/process_authors.php');
       break;
  case 'books_form1.php':
[B][COLOR="Red"]       include('./INCLUDES/process_books.php');[/COLOR][/B]
       break;
  default:
       $display_block = "Error - no option selected.";
}
?>

dbcp.php:

<?php
// Updated: Thursday March 24, 2011 - 1:40 PM
function pdo_dbc()
{
  $dsn = "mysql:host=localhost;dbname=PROJECT1";
  $user = "tester1";
  $password = "testuser";
//
   try {
      [COLOR="Red"][B]$dbh[/B][/COLOR] = new PDO($dsn, $user, $password);
      [COLOR="Red"][B]$dbh[/B][/COLOR]->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
      return ([COLOR="Red"][B]$dbh[/B][/COLOR]);
   } catch (Exception $e) {
      $emsg = $e->getMessage();
      include('./INCLUDES/dbcp_error_msg.php');
   }
}
?>

The calling script: process_books.php

*** 
function search($title, $bookid) {
    echo "Entering Search Function...";
//*****************************************************************************/
//*                           S E A R C H                                     */
//*****************************************************************************/
  if (($_POST['bookid']) != NULL) {
      $record_key = $_POST['bookid'];
      $field = 'bookid';
  }else{
      $field = 'title';
      $record_key = $_POST['title'];
  }
[COLOR="Blue"][B]The next line is the one that is generating the error message:[/B][/COLOR]
[COLOR="Red"][B]  $sth = $dbh->query("SELECT * FROM MYBOOKS where $field like '%$record_key%'");[/B][/COLOR]
  $query = "SELECT * FROM MYBOOKS where $field like '%$record_key%'";

  $result = mysql_query($query);

  $rows=mysql_affected_rows(); // Number of rows returned by the query.
  if (!$result) {
     $message  = 'Invalid query: ' . mysql_error() . "\n";
     $message .= 'Whole query: ' . $query;
     die($message);
  } else {
     if ($rows > 0) {
        while ($_POST = mysql_fetch_array($result, MYSQL_ASSOC)) {
              $authorid = $_POST['authorid'];
              $full_name = $_POST['full_name'];
              $bookid  = $_POST['bookid'];
              $authorid2 = $_POST['authorid'];
              $title = $_POST['title'];
              $isbn = $_POST['isbn'];
              $type = $_POST['type'];
              $cover_type = $_POST['cover_type'];
              $pages = $_POST['pages'];
              $copyright = $_POST['copyright'];
              $date_finished = $_POST['date_finished'];
              $has_been_read = $_POST['has_been_read'];
              $needed = $_POST['needed'];
        return array ($rows, $bookid, $authorid2, $title, $isbn, $type,
                   $cover_type, $pages, $copyright, $date_finished,
                   $has_been_read, $needed, $fname, $lname);
        }
     }
  }
}

[B][COLOR="Blue"]The code below calls the search function listed above:[/COLOR][/B]
***
//*****************************************************************************/
//*                 S E A R C H   B Y   T I T L E                             */
//*****************************************************************************/
  case 'Search':
      echo "Entering Search...";
       list ($rows, $bookid, $authorid2, $title, $isbn, $type, $cover_type,
           $pages, $copyright, $date_finished, $has_been_read, $needed,
           $full_name) = [B][COLOR="Red"]search($title,$bookid)[/COLOR][/B];
       if (is_null($rows)) { // If no rows were returned from query.
          $display_block = "No books were found.";
       }
[COLOR="Green"][B][I]I know the code below this won't work with PDO, but the error is prior to this code, so I will 
modify it after I fix the "non-object" error above! [/I][/B][/COLOR]
  $query = "SELECT * FROM myauthors WHERE authorid = '$authorid2'";

  $result = mysql_query($query);

  $rows=mysql_affected_rows();

  if (!$result) {
     $message  = 'Invalid query: ' . mysql_error() . "\n";
     $message .= 'Whole query: ' . $query;
     die($message);
  } else {
     if ($rows < 1) {
//        echo "NO AUTHORS RETURNED<br>";
     }else{
        while ($_POST = mysql_fetch_array($result, MYSQL_ASSOC)) {
               $id  = $_POST['id'];
               $authorid = $_POST['authorid'];
               $full_name = $_POST['full_name'];
        }
     }
  }
break;

Any suggestions or help will be greatly appreciated!

[bradgrafelman]

Variable $dbh is not declared inside the scope of the function. If you want to use the variable you've defined outside of that function, then you should pass the variable into the function as a parameter.

[peterv3]

bradgrafelman,
Your reply makes sense. The question I have is how do you pass the $dbh from one script file to another? Below is another section from the process_books.php file that works perfectly using the $dbh handle. I don't understand why this works when the other doesn't:

  case 'List':
//*                              L I S T                                      */
  include("./INCLUDES/display_books.php");
  break;

  default:
     echo "**** ERROR: Default - process_books.php ****<br>";
     echo "**** Option: $option_switch<br>";

This is the included script display_books.php called by the list case (the use of $dbh is hilighted in red):

<?php
// Updated: Wednesday March 23, 2011 - 3:17 PM
try {  // $dbh is passed by dbcp.php
   $bookid = $_POST['bookid'];
// GET COUNT OF RECORDS TO BE RETURNED
   if (($_POST['bookid']) != NULL) {
       $query1 = "Select COUNT(*) from MYAUTHORS INNER JOIN MYBOOKS ".
               "USING (authorid) ".
               "WHERE bookid = '$bookid'";
   } else {
      $search_type = $_POST['search_type'];
// If clause sets clauses needed for ALL BOOKS branch.
      if ($search_type != 'all_books' ) {
          $AND_CLAUSE = "AND needed != 'Y' AND needed != 'M'";
          $WHERE_CLAUSE = "WHERE needed != 'Y' AND needed != 'M'";
      }
// BY NAME
      if (($_POST['full_name']) != NULL) {
         $full_name = $_POST['full_name'];
         if (($_POST['search_type']) == "needed_only") {
// NEEDED
            $query1 = "Select COUNT(*) from MYAUTHORS INNER JOIN MYBOOKS ".
                    "USING (authorid) ".
                    "WHERE full_name = '$full_name'".
                    "and ( needed = 'M' || needed = 'Y' )";
         } elseif (($_POST['search_type']) == "not_read") {
// UNREAD
            $query1 = "Select COUNT(*) from MYAUTHORS INNER JOIN MYBOOKS ".
                    "USING (authorid)".
                    "WHERE full_name LIKE '%$full_name%'".
                    "AND has_been_read = 'N'";
         } else {
// ALL BOOKS
            $query1 = "Select COUNT(*) from MYAUTHORS INNER JOIN MYBOOKS
                           USING (authorid)
                           WHERE full_name LIKE '%$full_name%'
                           $AND_CLAUSE";
         }
      } else {
         if (($_POST['search_type']) == "needed_only") {
// NEEDED
            $query1 = "Select COUNT(*) from MYAUTHORS INNER JOIN MYBOOKS ".
                    "USING (authorid)".
                    "WHERE ( needed = 'M' || needed = 'Y' )";
         } elseif (($_POST['search_type']) == "not_read") {
// UNREAD
            $query1 = "Select COUNT(*) from MYAUTHORS INNER JOIN MYBOOKS ".
                    "USING (authorid)".
                    "WHERE has_been_read = 'N'";
         } else {
// ALL BOOKS
            $query1 = "Select COUNT(*) from MYAUTHORS INNER JOIN MYBOOKS ".
                    "USING (authorid)".
                    "$WHERE_CLAUSE";
         }
      }
   }
// Per the PHP PDO manual the following if statement uses "=" not "==".
   if ($stmt = $dbh->query($query1)) {
      $rowCount = $stmt->fetchColumn();
   } else {
      $i = $dbh->errorInfo();
      die('Database error: ' . $i[2]);
   }
   if ($rowCount > 0) {
      include('display_books_heading.php');
      $list_order = $_POST['list_order'];
      $type = $_POST['type'];
      if ($list_order == "needed") {
         $ascORdesc = "desc";
         $list_order == "needed, full_name";
      } else {
         $ascORdesc = "asc";
      }
      if ($bookid != NULL) {
         $query2 = "Select * from MYAUTHORS INNER JOIN MYBOOKS ".
                   "USING (authorid) ".
                   "WHERE bookid = '$bookid'";
      } else {
      if (($_POST['search_type']) == "needed_only") { // List All Books!
         if ($full_name != NULL) {
// NEEDED Books from One Author.
            $query2 = "Select * from MYAUTHORS INNER JOIN MYBOOKS
                       USING (authorid)
                       WHERE full_name = '$full_name'
                       AND   ( needed = 'Y' or needed = 'M' )
                       ORDER BY $list_order, full_name";
         } else {
// NEEDED Books from ALL Authors.
            $query2 = "Select * from MYAUTHORS INNER JOIN MYBOOKS
                       USING (authorid)
                       WHERE ( needed = 'Y' or needed = 'M' )
                       ORDER BY full_name, $list_order $ascORdesc";
         }
      } elseif (($_POST['search_type']) == "not_read") {
            if ($full_name != NULL) {
// ALL unread books from One Author.
               $query2 = "Select * from MYAUTHORS INNER JOIN MYBOOKS
                          USING (authorid)
                          WHERE full_name LIKE '%$full_name%'
                          AND   has_been_read = 'N'
                          ORDER BY $list_order";
            } else {
// ALL unread books.
               $query2 = "Select * from MYAUTHORS INNER JOIN MYBOOKS
                          USING (authorid)
                          WHERE has_been_read = 'N'
                          ORDER BY $list_order";
            }
         } else {
            if ($full_name != NULL) {
// Exclude "needed" books if search type is all_books.
// List All Books for a particular Author.
               $query2 = "Select * from MYAUTHORS INNER JOIN MYBOOKS
                          USING (authorid)
                          WHERE full_name LIKE '%$full_name%'
                          $AND_CLAUSE
                          ORDER BY $list_order";
            } else {
// NEEDED OR NOT READ BRANCH>
               if ($list_order == "needed") {
                  $list_order = "needed DESC, full_name ASC";
               }
// This is the default branch where ALL books are displayed!
               $query2 = "Select * from MYAUTHORS INNER JOIN MYBOOKS
                          USING (authorid)
                          $WHERE_CLAUSE
                          ORDER BY $list_order";
            }
         }
      }
} else {
   $display_block = "No books match search criteria.";
   echo "No books match search criteria.";
   exit();
}
$stmt = [COLOR="Red"][B]$dbh[/B][/COLOR]->prepare($query2);
//   $stmt->bindParam(':var1', $var1, PDO::PARAM_STR);
$stmt->execute();
//
$booknum = 0;
while ($row = $stmt->fetchObject()) {
      $bookid = $row->bookid;
      $authorid = $row->authorid;
      $title = $row->title;
      $isbn = $row->isbn;
      $type = $row->type;
      $cover_type = $row->cover_type;
      $pages = $row->pages;
      $copyright = $row->copyright;
      $date_finished = $row->date_finished;
      $has_been_read = $row->has_been_read;
      $needed = $row->needed;
      $full_name = $row->full_name;
      if ($needed == 'Y') {
         $class = "needed";
         $Needed = "Needed";
      } elseif ($needed == "M") {
          $class = "maybe";
          $Needed = "Maybe";
      } else {
         $Needed = "";
         if ($has_been_read == NULL) {
            $class = "not_read";
         } else {
            $class = "item";
         }
      }
      $booknum = $booknum + 1;
?>
.
. code here deleted due to post size restriction.
.
}
catch (PDOException $e)
{
  echo 'PDO Exception Caught.<br> ';
  echo 'SQL Query: ', $sql;
  echo '<pre>';
  echo 'Error: ' . $e->getMessage() . '<br />';
  echo 'Code: ' . $e->getCode() . '<br />';
  echo 'File: ' . $e->getFile() . '<br />';
  echo 'Line: ' . $e->getLine() . '<br />';
  echo 'Trace: ' . $e->getTraceAsString();
  echo '</pre>';
}
$dbh = NULL;
?>

If you can help me out with this, like syntax or other suggestions, I'd greatly appreciate it.
Peter V.

[johanafm]

It's all about "scope", or in other words lifetime and visibility of things. In the case with display_books.php above, you do not pass anything from one script to another. Those files are actually put together to form the script. You just do not store it all in one file.

If you have 2 files
1.php

stuff();
more_stuff();
require '2.php';
stuff();
stuff_again();

And 2.php

second_file_start();
stuff();
second_file_end();

Then when the script is run, the code turns into (without the comments)

stuff();
more_stuff();
/* file 2 */
second_file_start();
stuff();
second_file_end();
/* file 2 ended, back in file 1 */
stuff();
stuff_again();

The only difference is that you can use "return $val" from a required/included file and catch that value in the file that did the include/require, which is not otherwise possible.

# file1.php
echo require 'file2.php';

# file2.php
return "I'm file2.php";

So if you declare $dbh in file1, it's also accessible in file2 (assuming you are still in the same scope).
Global scope is what your script starts in. Any code inside a function has its scope within that very function.

Consider

# global scope
$dbh = db_connect();

# if you require/include file2.php here, it will have access to $dbh
# in exactly the same manner as if you used it in this file, i.e. you can do this
do_stuff_with_dbh($dbh);
# or this
$dbh = 'some_new_value';


# however, if you call a function, remember that the function's code is not in global scope
function foo(&$same_dbh_as_in_global_scope, $copy_of_dbh)
{
	# any code inside this function has its scope limited to this function
	# $dbh is not in this function's scope, it's in global scope, so you can't use it
	# unless it's passed along as a parameter (disregarding the global keyword
	# and globals array)

# you can however use $same_dbh_as_in_global_scope which is the exactly same
# thing in here as $dbh was outisde, since $dbh is passed by reference
# if you change $same_dbh_as_in_global_scope you change $dbh in global scope
echo $same_dbh_as_in_global_scope;
$same_dbh_as_in_global_scope = 'a';

# $copy_of_dbh contains the same data as the global $dbh did initially when this
# function was called, but is not the same variable. Thus you can change
# $copy_of_dbh without affecting global $dbh
echo $copy_of_dbh;
$copy_of_dbh = 0;
}

echo $dbh;
foo($dbh, $dbh);
# but $same_dbh_as_in_global_scope can't be used here since you're outside
# that function's scope again. Same with $copy_of_dbh
echo $dbh;

[peterv3]

johan, thank you very much for your thoughtful and complete explanation of the problem. I've tested what you told me, and it works great. I'm now in the process of making the changes to the way my scripts are written. This was a very important part of my learning process, and I'm extremely grateful. I'm going to leave the post open, just in case I have any more related questions. I'll close it when I have made all the modifications, and they work.
Peter V.