Question

I’m trying to learn to write a WordPress plugin by setting myself a goal of writing a user generated glossary plugin after I asked people on Twitter what would be useful (well I may as well use my learning experience to be useful for more than just me).

Anyway, on installation the plugin sets up a database table, and adds some test data to it. Then when the content is displayed a foreach loop changes each phrase and replaces it with a DHTML floaty box.

The problem is, however, I can’t work out what’s going on with the register_activation_hook; it may be being called and the SQL is failing or it may not be being called (either way I don’t have an extra table in the database after I activate the plugin).

The hook looks like this:

register_activation_hook(__FILE__, "bot_install");

And the bot_install code like this

function bot_install()
{
    global $wpdb;
    $table = $wpdb->prefix."sh_gloss";

    $structure = "CREATE TABLE $table (
        id INT(9) NOT NULL AUTO_INCREMENT,
        phrase VARCHAR(80) NOT NULL,
        desc VARCHAR(255) NOT NULL,
    UNIQUE KEY id (id)
    );";
    $wpdb->query($structure);

    // Populate table
    $wpdb->query("INSERT INTO $table(phrase, desc)
        VALUES('Scott Herbert', 'Rockstar Programmer')");

}

OK so firstly please forgive the ego database entry, it’s just for testing…

Secondly is there something I should have seen that I’ve missed?
And thirdly (and most importantly) how can I debug “bot_install”? Can I just add statements like:

echo "in xxxx";

or will that mess up the headers (since I guess all this code is ran before the main output).

Answer 1

I know nothing about WordPress, but…since there is no error handling in the code, how do you know that $wpdb is a valid database connection handle, and how could the code detect that something is not working – for example, the CREATE TABLE statement failed? The code apparently blindly (blithely) assumes nothing can or will go wrong, but my experience is that things can and do go wrong.

---

I’m still not the expert, but the URL referenced says:

Run Any Query on the Database

The query function allows you to execute any SQL query on the WordPress database. It is best to use a more specific function (see below), however, for SELECT queries.

<?php $wpdb->query('query'); ?> 

query

(string) The SQL query you wish to execute.

The function returns an integer corresponding to the number of rows affected/selected. If there is a MySQL error, the function will return FALSE. (Note: since both 0 and FALSE can be returned, make sure you use the correct comparison operator: equality == vs. identicality ===).

[…]

Examples

Delete the ‘gargle’ meta key and value from Post 13.

   $wpdb->query("
       DELETE FROM $wpdb->postmeta WHERE post_id = '13'
             AND meta_key = 'gargle'");

So, presumably, if the CREATE TABLE operation fails, you will get a FALSE back from it, which you can test with the appropriate operator – I’m not sure which one it is.

Further down, on the subject of errors, the page says:

Show and Hide SQL Errors

You can turn error echoing on and off with the show_errors and hide_errors, respectively.

<?php $wpdb->show_errors(); ?>
<?php $wpdb->hide_errors(); ?> 

You can also print the error (if any) generated by the most recent query with print_error.

<?php $wpdb->print_error(); ?> 

Finally, for debugging while under initial development, it won’t matter too much if the response is garbled as long as you can see the information.