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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.
At the end of the last movie I gave you an assignment to try for yourself. That is to take everything that we learned about find subject by ID and to create your own version of find page ID. Hopefully that went well for you. We'll take a look at the results to make sure that we have the same thing and then we'll talk about how we can refactor the page selection. So the first thing we're going to look at is functions.php and I've got find_page_by_id. It's a pretty simple function for you to create because you can actually just take find_subject_by_id. Copy it and then just change every instance of the word subject to say page instead.It's exactly the same thing. And in fact this is the same thing that you use every time you want to read back a single record from the database.
Find whatever it is by ID. It's going to look very similar to this. So this is a good template to keep around and reuse. If you don't have the same thing as me, go ahead and pause the movie and you can copy all of this down. I'm going to go ahead and move over to manage content.php. Where I've also done some copy and pasting. I took my current subject, and menu name display, and I used it down here as current_page. Again, just swapping in every time I see subject, swapping in page. I took one additional step. I moved the H2 inside my if statement, so that it can be conditional as well. Instead of just saying manage_content, it now says manage_subject or manage page. I thought that was a useful improvement, because otherwise, as I click around, I don't know whether I'm on a subject or a page.
Menu name doesn't give that away. Menu name is the same for both. So now, we can tell whether we're looking at a page or a subject. Okay so again, you can pause the movie and copy that down if you need to. But we're not ready to talk about how we can re-factor this. So, one of the first things that I noticed about this is just that there's a lot of code up here for selecting the page. And the more code that's down here for selecting the page. And I think we can clean up the relationship between those two a little bit. The first thing I notice is that I'm doing this setting of current subject here.
I'm doing it as I am about to use it. I like to do these finding and setting up of variables as early on the page as possible to get them set up. And to keep them out of the display or presentation of the information. So if possible, it's not always possible sometimes we are inside of a loop and we have to do it down there. So when possible I'm going to put it up here instead, This is the same conditional statement, right? I'm checking to see if the subject is set. If its set, then let's set select subject ID. And let's find the current subject. Let's jump back down here.
We can do the same thing for page, remove all of that. I'll put this up at the top. We will select our page ID. And then we'll set current page right afterwards. Now, I think that's an improvement. I think it's a little cleaner down here. We're just dealing with the display of these different things. Now, I also noticed, though, that selected subject ID used to make a lot of sense before. Right? We were checking to see for the presence of selected subject ID, but we're really just working with current subject. Why can't we just check for that? Right? Current subject is either going to exist or it's going to be null. So let's use that instead.
So if it's null, then this Boolean will evaluate the false. Now you could use is null, or if not is null is there, but this works just the same. This Boolean expression if we have a current subject, then do this. If we have a current page, then do that. The only problem is we need to watch for our default values. Because here we have a subject we want to make sure that we still also have a current page set. Null, and let's do the same thing for current subject, equals null.
And here as well. Then do current subject equals null or current page equals null. Okay, so now we've cleaned all that up and now it should still work. Let's just make sure our refractors still work. We reload the page, we click around and nothing has changed. Okay, so that's a good refractor. So this, to me, looks a little cleaner down here now. But I've kind of made a mess up here at the top. This is a, a big jumble now.
At least I'm doing it all in one place. But I think it can be cleaned up a little bit. And I'm noticing, for example, that I'm setting selected_subject_id here so that I can just reuse it here. Why not just use this value? The only other time that I'm using selected subject ID is down here in the navigation. We'll get to that in just a second. For now, let's go ahead and just take this and let's replace it. Let's say, alright, we're going to use that there instead and we'll do the same thing here with selected page ID. Now we're on the way to actually getting rid of selected subject ID and selected page ID. Get rid of those.
Right? So it just goes directly to it. Just take this value, send it in here. It's going to do MySQL real escape string, so we don't need to worry about the safety of it or anything like that, it's going to get escaped. So now we're going to just have either a current subject or a current page. This will work except for the navigation. Let's just comment out our navigation for a second and let's just try it. Let's come back over here and let's reload the page. You see that it works with page one, page three or subject three.
Right? I'm just typing it into the url up here since I don't have a navigation. Problem is, when we add the navigation to it, this is navigation wants these IDs. So, how can we set up an ID? Well, we could just send it this same value. We could say, let's drop that in, get subject, get page. Right. There we go. That should work right. We're just sending those same values into navigation. Let's reload the page. Whoa, wait a minute. Notice here I get a warning that something hasn't been initialized, that's because one of these values doesn't exist.
At the moment, I'm on a subject page so Get_page doesn't exist. It goes to look for, and it's not there. We've moved outside of this very important is set, checking to see if it is set or not. So we don't want to do that, we want to stay inside of this is set. So what could we do instead? Well we could send current_page. We could say current_page and it should then have an ID, right? And same thing for current_subject. Now we're going to have the same problem.
In some cases current subject is going to exist and some pages current page is going to exist, but they're not going to exist at the same time. Now we actually might be able to call a key on null and have it not blowup on us. But that's beside the point, it's really not a good programming practice. Instead, let's just pass in the current_subject and the current_page. Whatever they maybe, they maybe an associated array or it maybe null, and we'll just handle it inside navigation. Navigation will expect to get one or the other. It will either expect an associative array or it will expect null.
Let's just close that up. Let's go back over to our functions and make that change. So now, instead of navigation taking two arguments. The currently selected subject_id, we're going to say the current_subject array or null and this one will be the current page array or null. And then let's make that change here. So that we're expecting either a subject or a page. And then just here, we just have to check, right? We may be getting back a subject, which we can call ID on. Or we may be getting a page that we can call ID on. However, we might not, we might be getting null. So let's just add an additional condition here.
That says, if subject and subject id is equal to subjects. So if we have a subject, and if the subject id is equal to subject id, now notice what we just did here. This should be a subject array, and page array, to keep them separate from what we're using inside our loop. Alright. And down here, call this one page array and we'll just check also for page array being present.
So if we have a page_array and page_id is equal to page_array's ID. Alright a little cleaner let's take a look and see if it works still. Come back here and reload our page there we go. Now we are clicking around and we are getting the same results. We have made things different in our code but the functionality is the same that's what we want to do when we are re factoring. I find this all to be a little cleaner and easier to use. Let's do one last re factor here before we leave this. I'm just going to take all of this and I'm going to cut it, take it out, I'm going to go back to my functions.php and I'm going to make a new function for it.
So, let me just take find navigation and right below it, let's, right here, let's do function find selected page. It's not going to take any arguments because it is going to use GET, and then it's going to set values based on that. This is a super global, it's available everywhere. We don't have to call global scope on it. So find_selected_page is all we're going to have to call now from over here, and it's going to do all that work for us.
All right so we just wrapped it all up. We don't need to echo it or anything. We just need to tell it to find selected page and what that's going to do is set values for us for current page. Let's come back over here. There's one issue though. We need to return either current page and current subject. Right, we can do that down here. Return. We can return the array and then catch those values. Or we can just declare them as being global. That will essentially say that these are in the global scope, that that's where we're working on them from, global subject, and current page.
Even though they didn't exist before they got here, it's okay, we're creating them in the global scope. We're referring to them in the global scope. So here when they get defined It's the global scope where we're using them and that means that they're still available to us once we leave the function. So let's just close all that up now. And let me just put a return here so that separates it. Let's go back over to Firefox. Let's reload the page, let's click around and everything still works as expected. Notice how much cleaner that is? All of that business gets taken care of here in this function, and we can really focus on just the display here, really just focus on that aspect of it. The presentation of the data that we've already set up. I think this is a real improvement.
Okay. Now that we have our subject and page reading down, we're ready to move on to the next part of CRUD, which is create.
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