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In WordPress: Creating Custom Widgets and Plugins with PHP, Drew Falkman teaches PHP developers how to create custom functionality for WordPress 2.0 through 3.0 using widgets and plugins. This course starts by installing and setting up WordPress 3.0 on both Mac and Windows, then provides an in-depth look at tasks related to these WordPress add-ons: installing and administering, building and customizing, creating editable options and database tables, working with posts and pages, and utilizing jQuery and AJAX. There are also tutorials dedicated to promoting a widget or plugin, adding security, and localizing the interface. Exercise files are included with the course.
The reason we've been looking at the WordPress database and why we might want to use it is because oftentimes our plugins might actually need their own data structures. Think about a program that collects statistics, or maybe you want to build a whole product database to display and integrate for a client that you have. Whatever the reason, WordPress gives us a bunch of tools to create our own tables in the WordPress database. To create our data structure, we're going to need to write a function that creates it in SQL. I've created here a plugin, and this will basically save the user agent from the browsers when they come to the site.
We can then parse it out later and show whatever statistics we want about what types of browsers are visiting our site, whether people are using iPhone, Android, or a regular computer. So, in order to access the database, I need to globalize the wpdb variable, so that I can access it in my function. Then I'm going to create a name for my table. So I have a variable that I'm creating called table_name, and I'm going to use this special property called prefix, to get the prefix of the database. This is a best practice, because oftentimes people will have a special prefix they store in their WordPress installation.
So that way every table inside of the WordPress database will have a prefix. It's usually WP by default, but this allows them to have databases that share WordPress but also other functionality as well. And we're going to create our own table name and call it "bdetector" to store our information. So now what we're going to do is we're going to go in and determine if the table already exists. If it exists, then we won't create it. However, if it doesn't exist, we're going to want to create it. So, I'm going to create an if statement, and the way I determine if the table exists is I'm going to use the wpdb class, and I'm going to call the get_var.
If you remember, this is what I used to get a single field from the database. Now I'm going to run some SQL, and particularly I'm going to call 'SHOW TABLES LIKE ', and then I'm going to append on my table_name. So, if this is not equal to my table_name, then that means it didn't find it in the database. So it's either going to be the table_ name if it exists, or it's going to be empty if it doesn't exist. If it doesn't exist, I'm then going to run my query. So first I'm going to set up my query.
I'm just going to create a variable called sql, and I'm going to write it out. So we're going to say 'CREATE TABLE ', and remember you always want to have a space in here. Otherwise, when you append variables, the text is going to run up against one another and cause database errors. So, I'm going to put my table_name in here, and now I'm going to write out what the table looks like. There's going to be an id, which is going to be an INTEGER of size 10. It's UNSIGNED; in other word, it is not going to be negative. And we're going to set it to be AUTO_INCREMENT.
This is our key essentially. I'm going to have a hit_date. So I'm going to store when the user came, that's going to be a TIMESTAMP, and we're going to default it to CURRENT_TIMESTAMP. What that means is the database is automatically going to create this value if one doesn't exist for the current time. So, all I need to do is insert a record in here, and it will timestamp it for me. The user_agent is what I'm going to store, and that I'm going to get from the browser. And that's going to be a string, and I'm just going to give it 255.
Most of them aren't going to be that long, but it gives me some flexibility. And then lastly, I'm going to declare my PRIMARY KEY to be the id. You may need to make sure that there is a couple of spaces in there. Okay, so there is my query. Now, in order to actually do this, I'm going to use this special function called dbDelta. This offers some assistance. Essentially what it will do is it'll take this pattern here--and you want to write it just like this with a new line for each of the columns you're going to create in the database-- dbDelta will essentially, if there is any changes, it will update the table.
If not, it will just create it as is. If it's the same, it won't do anything. It's a very helpful function. In order to use it, I'm going to have to include it, and the way we include things is to use this require_once function. I'll specify the absolute path, which is the absolute path of my WordPress installation. Then I'm going to say in the WordPress admin directory, in the includes directory, and it's called upgrade.php. Incidentally, when you create your own plugins, you're going to want to use this same methodology to include additional files if you break it up into multiple files.
So now that we've included this, we can call dbDelta, and we'll pass to it our query. So, this will then create our database. Another good idea to do, and this is optional, is we're going to add an additional option. So we're going to use the option database to set up an option so that we can have a version of this database, so that if we do want to do updates to this particular plugin in the future, we can simply look at our option and see what version the database is and update if necessary.
So, I'm going to call the add_ option function, and I'm going to call it bdetector, so it's unique and then database_version, and we'll just set it to 1.0. So, now that I have all this set up, I'm going to make sure that this runs for the activation action. So, if you recall, the way we do that is we call register_activation_hook. We pass the file, and we can use file, which represents the current file, and then the function that we want to execute when we activate this plugin.
So, bdetector_activate. So that's all we need. This is our plugin, and this will essentially create the database. Let's go ahead and go into our WordPress admin, go to the Plugins page, find our Browser Detector Plugin, which is right here, and go ahead and activate it. When it was activated, it should have created this table in the database. So let's go ahead and look at our MAMP installation. Let's go into phpMyAdmin, look at wp _test, and you can see we have this table wp_bdetector.
When I click on it, you can see it created an id, a hit_date, and a user_agent. So, to create your own database in WordPress, it's a good idea to use that dbDelta class in upgrade.php. This is going to upgrade the table using SQL query, and typically we're going to add this as an activation hook. And now you've got your own database table, so you can start storing things with your plugins. Creating your own database table in WordPress is a fairly straightforward process. You need to create your SQL that's going to create the table using the CREATE TABLE statement.
Make sure in your table_name, you use the wpdb prefix property to get the prefix that the user is using for their WordPress installation. When your statement is ready, simply call the dbDelta function that you can find in the upgrade.php class. Now let's go on and look how we can insert and update data into our database table.
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