Mass import users into WP

I am working on a complex blog/e-commerce system together with my colleagues at @ntw. I had to import some 10.000 users into WP. The task was easier than expected. The basic idea is leveraging on the wp_insert_user($userdata) function, defined in wp-includes/registration.php. If you look at the source, you’ll see that $userdata is an array containing a number of keys:

	* The $userdata array can contain the following fields:
	* 'ID' - An integer that will be used for updating an existing user.
	* 'user_pass' - A string that contains the plain text password for the user.
	* 'user_login' - A string that contains the user's username for logging in.
	* 'user_nicename' - A string that contains a nicer looking name for the user.
	*		The default is the user's username.

The other keys are user_url,user_email, display_name, nickname, first_name, last_name, description, rich_editing, user_registered, role, jabber, aim, yim; for more detal consult the source itself.

My script goes like this:

<?php
include 'wp-blog-header.php'; 
include 'wp-includes/registration.php';   
include 'wp-includes/pluggable.php'; 
ini_set("memory_limit","1024M"); 
ini_set("max_execution_time", "240");
global $wpdb;
?>
 
<h1>Importazione utenti EC</h1>
 
<?php
$connection = mysql_connect("host", "user", "password") or die("Unable to connect to MySQL");
mysql_select_db("database", $connection) or die("Unable to connect to the database"); 
$result = mysql_query("SELECT * FROM source_users ;");
	while ($row = mysql_fetch_object($result)) {
		echo "<strong>ID:</strong>".$row->id." <strong>login:</strong>".$row->user_name." <strong>password:</strong> ".$row->password." <strong>e-mail:</strong>".$row->email_address." <strong>name:</strong> ".$row->name." <strong>surname:</strong> ".$row->surname."<br/>";  
		// Add the ID to trick WP
		$add_id = "INSERT INTO ".$wpdb->users." (id, user_login) VALUES (".$row->id.",'"."$row->user_name"."' ); ";
		 mysql_query($add_id) or die(mysql_error());
		// Add the rest
		$userdata = array(
		 'ID' => $row->id,  
		 'user_login' => $row->user_name,
		 'user_pass' => wp_hash_password($row->password),
		 'user_nicename' => $row->user_name,
		 'user_email' => $row->email_address,
		 'first_name'  => $row->name,
		 'last_name'  => $row->surname,
		 'role' => 'subscriber'
		);                          
		wp_insert_user($userdata) ;
	}
}
 
 
mysql_close($connection);

Some highlights:

Import all the WP files you need
Change PHP memory and time limits if you have many records
Explicitly encrypt the password with wp_hash_password. I have no idea why this is necessary, the WP code should do this by itself; but trust me, it is.

Since we are using the wp_insert_user() function, WP will crate records both in the users and in the usermeta tables.

A last warning. This huge amount of users could conflict with your php settings. To get WP working properly I had to add this line to wp-config.php: