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PHP is a popular, reliable programming language at the foundation of many smart, data-driven websites. This comprehensive course from Kevin Skoglund helps developers learn the basics of PHP (including variables, logical expressions, loops, and functions), understand how to connect PHP to a MySQL database, and gain experience developing a complete web application with site navigation, form validation, and a password-protected admin area. Kevin also covers the basic CRUD routines for updating a database, debugging techniques, and usable user interfaces. Along the way, he provides practical advice, offers examples of best practices, and demonstrates refactoring techniques to improve existing code.
In this movie, we're going to use what we've learned about database connectivity in our application to connect to the database. And then create a list of subjects on manage content.php. We're going to start by just listing all of the subjects. In the next chapter, we'll add pages to it and see how to bring up page content. So go back and review database connectivity if you need a refresher. Remember there's five steps that we need to follow. We're going to create a database connection, form our database query, use the returned data if any. Release the returned data, and then close the database connection. Let's start by opening up that file that we worked with earlier. That's inside our Sights folder, inside Sandbox and it's called databases.php. Let's just open that up for reference.
This has all of that connection in there, and we can just copy this over. We're going to add it to our managedcontent.php page, so let's add it right here before we even do the functions. Let's do it right at the very beginning, and we're just going to grab all of this PHP here for step 1, which is create a database connection. So just copy that, let's bring it over and paste it in. So now this will create our connection and it will test to see, was there an error. If there was an error the database connection will fail. Then the second thing is to perform a database query.
Let's do that as well but let's don't put that block here at the very top, let's do that one after we've done our functions. Before we start actually doing the layout we're going to do it right here, we're going to perform our database query. And then, let's drop down here to use return data if any, and it just so happens we were working with subjects before. That's what we were bringing back was displaying a list of the subject. Is perfectly appropriate for use to still use, make sure that you get the UL tags that go with it we'll copy that. And where we want to put this is inside the navigation. So inside the navigation, instead of that nbsp, we want to get rid of that and instead use the return data.
That's going to be our list inside the navigation. And then, release the return data. We'll do that after we're done with it so, let's do it right here after Main. Right before we do our footer, we'll release the data that we were working with. And then last of all, close the database connection. And that can be the very last thing that we do down here after the footer. So, that's it. We just basically imported all of this code that we were working with before from just a very simple framework. We brought it all over so that we can work with it here in ManageContent.php.
Let's bring it up and try it out. So, we'll go into Firefox. Here's my Manage Content page. I'll just hit Reload and there we go. About Widget corp and then it still shows the IDs after it in parentheses. That's fine for now. Go ahead and leave those. We can always remove them when we're finally done with it. Now, I'm also going to do one more thing to this, which is just to the UL, I'm going to give it a class of subjects. And that's going to make some style kick in for that, which will make it a little cleaner. It will just bring it over a little bit to the left. So, now that we have it working on this page. Let's improve it using what we learned in the last movie about making reusable assets for ourselves. Let's move our database connectivity to a file in the includes directory. So let's create a new file for ourselves, and let's just move some of this code over there.
What I want to do is move the database connection, which happens right here at the top. I want to take that out of here, cut it, i'm going to paste it in over here. And I'm going to save this as Save, Inside Widget Corp, inside includes and I'm going to call it db_connection.php. There we go. Now I can come back over here. And I will use require _once instead of Include. I'll use require_once. And instead of Functions, it's db_connection.
So now, all I have to do is make this line and voila, I've got a database connection. It's that easy. If some configuration changes about my database connection, I can come in here and it'll change it for my entire website. It's nice, huh? Alright, so let's close that up. Now notice here, the database query is unique to this page, though. At least for the moment. We'll come back to that and make improvements on it later. But for the most part, it's going to be unique to this page. Using the return data is unique to this page. And freeing the result I would say is also part of this page. You don't have to. You could move freeing the result to something at the end. It could happen for example in the footer, but then you always have to call your result, result.
And I like the fact that it bookends the query that I made up here. So I do a query up here, and I can see that I freed the result down here. However, closing the database connection can be moved somewhere else. And you could move it to a file called db_connection_close. And always have that at the one. But I also think that we can just take it, and we can move it into our footer. So lets close that up, and lets find our footer file. So we can just put it right here at the bottom of our footer. So once we're done with our HTML, the very last thing we can do is close the connection.
Now you don't actually have to close the connection, PHP figures it out if it gets to the end of the page and it's done and it still got this connection open. It says oh yeah, I guess I'd better close that. If no one else is going to bother doing it, I'll do it. So it will do it, but it's still a good practice to put it here. Now, because we might be using this footer on pages that are not database enabled, places where we did not ever open a connection. It's also a good practice to check and see whether a connection has been set before we start trying to close it. So let's just add a little statement here, if is set, connection, so if it's set, then close it.
And that's a little better. So now, if it's there, close it by the time you get to the end of the page. Because once we're done with our HTML, we probably don't need that database connection anymore. So, now if we go back to Manage_content.php, you can see that once again, we've slimmed down the page, quite a bit. By taking out all that database connectivity and putting it somewhere else. There's one more change that I want to make here. Notice that we tested that there was a query error and so, on every single page, I'm going to have this bit of code. Checking to see, did I get back a failed result. This is a perfect candidate for moving to a function, that's exactly what I'm going to do. I'm going to open up that functions.php, and I'm going to just write my first function here in this file.
Function, I'm going to call it confirm_query, and it's going to take, I'll call it result_set, instead of just simply result. And if there's not a result set. Then, let me just grab that same behavior we had the die, that's what I want. The die with that string database query failed. So now that I have this function I can just call confirmed query. Since I've loaded it in my functions here I'll have it available to me. Let's just call confirmed query on result.
I can take all of that out. To me, that's a little cleaner. Then I can just check, it's does a check to see did the query work or not, and then it moves on from there. And again, because I now have reusable code, if I want to make improvements to this. If I want to change the message that gets displayed or something else. I can just do it one place, and the way the confirm query gets handled will trickle down throughout my entire site. So let's just close all of that up, let's go back one more time to manage contact and make sure that the page still works, and it does. So there's one last thing that I want us to do before we leave database connectivity and that's just that i want us to open up the DB connection. And instead of having these variables that we defined here, a better way to do it is to use constants.
So I'm just going to copy and paste in an example of what I'm talking about. You can just define, all of these as constants instead. I'll get rid of those, and then instead of having it here, we'll DB server, DB user, DB Pass and DB Name. Now it's using constants for those instead of the variables. It's just a little bit better practice to do it this way since they are, in fact, going to be constant values. They're not going to vary, we would use constants for them. And let's save it and just one last time let's make sure we didn't break anything.
Go back over to Firefox and reload our page and you see this still comes up just fine.
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