How to include $wpdb in wordpress plugin?

Question

I've been developing for some time on a plugin in wordpress, but one problem keeps bugging me. I want to export a database-table as an excel file and therefor i need access to the global $wpdb->variable from a file in my plugin directory.

I found a blog entry that explains what classes i should include, but this doesn't work (link is below). As you can see, i do a var_dump, but it never reaches that point. If i leave the includes of wp-config and wp-load out of the code, the dump returns NULL, so i'm guessing there is a problem with the imports.

Anyway, i was hoping someone could help me with this problem. I don't necessarily need a fix for my approach, I just need a way to export an array of data (fetched from my db) to excel in wordpress. Any help would be appreciated. Thanks in advance.

http://www.notesbit.com/index.php/web-mysql/web-scripts/standalone-access-the-wordpress-database-using-wpdb/

include_once('../../../wp-config.php');
include_once('../../../wp-load.php');
include_once('../../../wp-includes/wp-db.php');

var_dump($wpdb);
$filter = get_where_clause();
$order = get_order_by_clause();

$data = $wpdb->get_results("SELECT * FROM " . $table_prefix . "team_data" . $filter . $order, ARRAY_A);

$result = array();

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EDIT: I cannot include the wp-config, it gives constant errors. I know where the bug is taking place, I just need to find a work-around. when looking at the wp-settings page (which is included by the wp-config) you will find this line of code:

foreach ( wp_get_active_and_valid_plugins() as $plugin )
    include_once( $plugin );
unset( $plugin );

this is where there is a bug. I just don't know how i should work around this bug.

EDIT 2: Problem solved. When including the file, i included the wp-config more than once (even though i stated it should only be included one time). I solved the problem by using the following code.

global $wpdb, $table_prefix;

if(!isset($wpdb))
{
    require_once('../../../../wp-config.php');
    require_once('../../../../wp-includes/wp-db.php');
}

Solution 1

If you're creating a WordPress plugin, you don't need to include those files manually.

If you want to export your table, why don't you create a function/class for it and pass the $wpdb to it (if you need it). You can also use the normal MySQLi-class (from PHP) do access your MySQL Database.

---

If you simply want to access the MySQL Database with the stored login-values which are used by WordPress, you can include the wp_config-file from the WordPress root-directory. It has some (self explaining) global fields which you could use to connect to your database:

include "WP-ROOT-PATH/wp-config.php";
$db = new mysqli(DB_HOST, DB_USER, DB_PASSWORD, DB_NAME);
// Test the connection:
if (mysqli_connect_errno()){
    // Connection Error
    exit("Couldn't connect to the database: ".mysqli_connect_error());
}

After that you have a instance of the MySQLi-class (as mentioned above) which you can use to access your Database.

I'm however not sure if this is the perfect way to go but it sure works.

---

To Debug WordPress (if something doesn't work and there is no Error-Message) you should activate debugging in the wp-config.php-file:

/**
 * For developers: WordPress debugging mode.
 *
 * Change this to true to enable the display of notices during development.
 * It is strongly recommended that plugin and theme developers use WP_DEBUG
 * in their development environments.
 */
define('WP_DEBUG', true);

Also, if you're testing your PHP-Scripts on a local server, you should turn the display_error to on in your php.ini-file:

; This directive controls whether or not and where PHP will output errors,
; notices and warnings too. Error output is very useful during development, but
; it could be very dangerous in production environments.
display_errors = On

However this should only be done on your local test-server, not in a productive scenario.

Solution 2

get away from hard solutions! and just use :

define( 'SHORTINIT', true );
require_once( $_SERVER['DOCUMENT_ROOT'] . '/wp-load.php' );

Comments

[Michiel Standaert]

I do have to include them manually, because if i want to trigger an excel download, i cannot do that from within the admin.php of wordpress (the header information cannot be passed, don't ask me why). So i call a php-file from my plugin-directory, but this cannot access the $wpdb variable or any other variable i would need to access the wordpress db for that matter.

[Lukas Knuth]

The header information can't be send because you change the header after something was already printed. You should (like i said) create a new class in a new file and pass it the $wpdb-Object.

[Michiel Standaert]

And how should i pass the $wpdb-variable to that class? because the way i am calling the file now is by redirecting to another php-page. (html shown below). <a href="../wp-content/plugins/myplugin/to_excel.php?filter=<?p‌​hp echo($filter_name) ?>" class="button-primary">Save as excel</a>

[Lukas Knuth]

Sorry, that was a misunderstanding on my side. I updated my post, take a look at it.

[Michiel Standaert]

Thank you for replying, I have gotten a little closer to solving the problem. I have updated my original post with some more explanation.