PHP with MySQL Essential Training
Illustration by Don Barnett

Deleting a subject


PHP with MySQL Essential Training

with Kevin Skoglund

Video: Deleting a subject

We've now taken a look at three out of the four types of CRUD actions. We have create, we have read and we have update, the last one is delete. And delete is simple by comparison, there's no form or anything like that to fill out. We just simply honor the request. The user says delete it, so we delete it. So we're going to do this on a new page Open up Text Mate and let's just save that as. This is going to be in Sites inside Widget Corp and then inside our Public folder. We're going to call it delete_subject.php.
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  1. 4m 8s
    1. Welcome
      1m 0s
    2. Using the exercise files
      3m 8s
  2. 15m 6s
    1. What is PHP?
      3m 52s
    2. The history of PHP
      2m 51s
    3. Why choose PHP?
      4m 10s
    4. Installation overview
      4m 13s
  3. 54m 53s
    1. Overview
      2m 33s
    2. Working with Apache Web Server
      6m 56s
    3. Changing the document root
      7m 24s
    4. Enabling PHP
      6m 16s
    5. Upgrading PHP
      3m 30s
    6. Configuring PHP
      10m 3s
    7. Installing MySQL
      5m 46s
    8. Configuring MySQL
      7m 24s
    9. Text editor
      5m 1s
  4. 31m 25s
    1. Overview
      3m 27s
    2. Installing WampServer
      5m 46s
    3. Finding the document root
      2m 24s
    4. Configuring PHP
      8m 12s
    5. Configuring MySQL
      5m 45s
    6. Text editor
      5m 51s
  5. 19m 12s
    1. Embedding PHP code on a page
      6m 43s
    2. Outputting dynamic text
      5m 55s
    3. The operational trail
      2m 27s
    4. Inserting code comments
      4m 7s
  6. 1h 18m
    1. Variables
      7m 50s
    2. Strings
      4m 38s
    3. String functions
      8m 54s
    4. Numbers part one: Integers
      6m 27s
    5. Numbers part two: Floating points
      5m 25s
    6. Arrays
      10m 0s
    7. Associative arrays
      6m 37s
    8. Array functions
      6m 33s
    9. Booleans
      3m 50s
    10. NULL and empty
      5m 15s
    11. Type juggling and casting
      8m 27s
    12. Constants
      4m 43s
  7. 27m 37s
    1. If statements
      6m 0s
    2. Else and elseif statements
      4m 16s
    3. Logical operators
      7m 30s
    4. Switch statements
      9m 51s
  8. 42m 15s
    1. While loops
      8m 41s
    2. For loops
      5m 59s
    3. Foreach loops
      8m 16s
    4. Continue
      8m 28s
    5. Break
      4m 8s
    6. Understanding array pointers
      6m 43s
  9. 37m 25s
    1. Defining functions
      8m 25s
    2. Function arguments
      5m 32s
    3. Returning values from a function
      7m 33s
    4. Multiple return values
      4m 53s
    5. Scope and global variables
      6m 2s
    6. Setting default argument values
      5m 0s
  10. 20m 18s
    1. Common problems
      3m 47s
    2. Warnings and errors
      8m 36s
    3. Debugging and troubleshooting
      7m 55s
  11. 57m 57s
    1. Links and URLs
      5m 33s
    2. Using GET values
      5m 35s
    3. Encoding GET values
      8m 41s
    4. Encoding for HTML
      9m 26s
    5. Including and requiring files
      7m 40s
    6. Modifying headers
      6m 45s
    7. Page redirection
      6m 43s
    8. Output buffering
      7m 34s
  12. 1h 3m
    1. Building forms
      7m 28s
    2. Detecting form submissions
      5m 59s
    3. Single-page form processing
      7m 57s
    4. Validating form values
      10m 40s
    5. Problems with validation logic
      9m 54s
    6. Displaying validation errors
      7m 23s
    7. Custom validation functions
      6m 28s
    8. Single-page form with validations
      7m 25s
  13. 28m 5s
    1. Working with cookies
      2m 49s
    2. Setting cookie values
      5m 55s
    3. Reading cookie values
      6m 1s
    4. Unsetting cookie values
      4m 51s
    5. Working with sessions
      8m 29s
  14. 48m 39s
    1. MySQL introduction
      6m 43s
    2. Creating a database
      7m 41s
    3. Creating a database table
      7m 42s
    4. CRUD in MySQL
      5m 48s
    5. Populating a MySQL database
      7m 32s
    6. Relational database tables
      6m 40s
    7. Populating the relational table
      6m 33s
  15. 56m 4s
    1. Database APIs in PHP
      4m 51s
    2. Connecting to MySQL with PHP
      7m 45s
    3. Retrieving data from MySQL
      8m 47s
    4. Working with retrieved data
      6m 12s
    5. Creating records with PHP
      6m 58s
    6. Updating and deleting records with PHP
      9m 6s
    7. SQL injection
      3m 5s
    8. Escaping strings for MySQL
      6m 45s
    9. Introducing prepared statements
      2m 35s
  16. 35m 58s
    1. Blueprinting the application
      7m 19s
    2. Building the CMS database
      5m 14s
    3. Establishing your work area
      4m 38s
    4. Creating and styling the first page
      4m 22s
    5. Making page assets reusable
      6m 36s
    6. Connecting the application to the database
      7m 49s
  17. 32m 49s
    1. Adding pages to the navigation subjects
      5m 58s
    2. Refactoring the navigation
      6m 7s
    3. Selecting pages from the navigation
      6m 2s
    4. Highlighting the current page
      5m 26s
    5. Moving the navigation to a function
      9m 16s
  18. 1h 45m
    1. Finding a subject in the database
      9m 48s
    2. Refactoring the page selection
      10m 52s
    3. Creating a new subject form
      6m 55s
    4. Processing form values and adding subjects
      11m 20s
    5. Passing data in the session
      9m 16s
    6. Validating form values
      9m 40s
    7. Creating an edit subject form
      8m 30s
    8. Using single-page submission
      7m 44s
    9. Deleting a subject
      9m 44s
    10. Cleaning up
      10m 37s
    11. Assignment: Pages CRUD
      4m 30s
    12. Assignment results: Pages CRUD
      6m 10s
  19. 39m 26s
    1. The public appearance
      8m 52s
    2. Using a context for conditional code
      11m 37s
    3. Adding a default subject behavior
      6m 9s
    4. The public content area
      5m 51s
    5. Protecting page visibility
      6m 57s
  20. 1h 3m
    1. User authentication overview
      4m 3s
    2. Admin CRUD
      8m 41s
    3. Encrypting passwords
      7m 26s
    4. Salting passwords
      5m 42s
    5. Adding password encryption to CMS
      11m 54s
    6. New PHP password functions
      3m 13s
    7. Creating a login system
      11m 28s
    8. Checking for authorization
      5m 48s
    9. Creating a logout page
      5m 40s
  21. 2m 4s
    1. Next steps
      2m 4s

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Watch the Online Video Course PHP with MySQL Essential Training
14h 24m Beginner Jun 04, 2013

Viewers: in countries Watching now:

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.

Topics include:
  • What is PHP?
  • Installing and configuring PHP and MySQL
  • Exploring data types
  • Controlling code with logical expressions and loops
  • Using PHP's built-in functions
  • Writing custom functions
  • Building dynamic webpages
  • Working with forms and form data
  • Using cookies and sessions to store data
  • Connecting to MySQL with PHP
  • Creating and editing database records
  • Building a content management system
  • Adding user authentication
Kevin Skoglund

Deleting a subject

We've now taken a look at three out of the four types of CRUD actions. We have create, we have read and we have update, the last one is delete. And delete is simple by comparison, there's no form or anything like that to fill out. We just simply honor the request. The user says delete it, so we delete it. So we're going to do this on a new page Open up Text Mate and let's just save that as. This is going to be in Sites inside Widget Corp and then inside our Public folder. We're going to call it delete_subject.php.

Alright, so there it is, there's delete_subject.php. And what is this page going to do? Well it's going to need to have the session. It's going to need our database connections. It's going to need our functions. So let's grab those from any of these other pages we were just working with. Open up new subject. At the top here. So let's just grab all of these. It's not going to display any HTML. So we don't need to output anything. We're simply going to process the request and then redirect them somewhere else.

Now I think it's also a good idea to check to see whether it's actually in the database or not. Strictly speaking you don't have to do that. You could just simply say, alright, whatever ID you give me, that's the ID I'm going to try and delete. Alright, but I think it's a better practice to actually go to the database first and do a query, say is it there and if it's there, then we do the delete. So if you remember under edit_ subject.php, we had a bit of code at the beginning here that does the find selected page and then checks to see if it has a current subject or not.

Now we actually don't need to find the selected page because that was really what we were doing for navigation. Instead we can just write our own here, it's not hard to do. We can just say, current subject equals find_subject_by_id. And then we'll pass it in, GET subject. So that's it. That will go to the database and look for it. We have that nice function for us that we can use here. And then, if it's not set then we'll redirect back to manage_content.php.

Now probably it will be set and in which case then we want to perform our delete. So for the delete, let's write our query. I'm going to go ahead and set id equal to current_subject id. It's not a step that's strictly necessary but it just reminds me and reminds you that we do need this id while we're doing the delete. And then our query, just going to be delete from subjects where id is equal to and then we'll use that id there. Limit 1. Now, you could break this up onto multiple lines. It's so short that I'm just going to go ahead and put it all on one single line. And then we know how to do our query result.

I should just jump over here and grab this bit here. And we're going to want mysqli_affected_rows also for delete statements. So lets just go over here. So there we go, so we'll perform the query. The result, if it has a result and the affected rows is equal to one, then we'll know that it succeeded. If not, then it failed. And before we were doing this. If we had a success, that's fine we can go ahead and keep that. And the only thing is we switch to using just a variable for failure. Let's say subject deletion failed and then we'll redirect them back to the manage_content page.

Let's go ahead and put them on the subject that we're looking at. Here we can't do that because the subject doesn't exist anymore. We just deleted it so we can't show them that subject but here we can. So that's it, that's all there is to deleting. We just load in all of our basic stuff, find the subject, make sure that it's there, construct our query, execute the query so that it deletes it. And then check to see did it happen or not and redirect them to a page accordingly. Let's save that, there's one other thing though, which is a question of where do we want to put this delete link. How's the user going to actually delete it.

Now you could put it a lot of places. You could put it just on the page here called manage_content, right? We could put it so that every time we have a subject just like we have edit, we could have another one that says delete. I think because delete is such a destructive action, I like to give it a little extra safeguards to that. You could put it there, certainly. I'm going to put on the edit subject page and I'm just going to come down here to the form for editing subject and right after, we have the edit subject and we have cancel. I'm going to add another one here  .

That's just going to put a non-breaking space. And so right after we have Cancel, let's add another link that's going to be for the deletion. So this is going to be delete_subject and of course, it needs to know what subject it's going to delete. Let's go here, Delete subject. Okay, so which one is it going to delete? php current_subject and id. I need to echo it, don't want to forget that.

That's it. Okay, so now I should have a link to it that's right there. Let's try that out. Let's go over here and let's go to test subject, edit subject, and now I have link here for delete subject. Let's try it, and there it is. Subject updated I didn't want that, I actually wanted subject deleted. Let me just go to my delete page and just change the message, subject updated, subject deleted. But it did delete, you can see that it disappeared. And same thing if we take sample subject, we could make it disappear just as well.

There is one additional thing that I want to show you. Again just because delete is such a destructive action. I think it's a nice thing if we come over to where we put our link for edit subject, and we just put a little bit of JavaScript on this link. So this is the only JavaScript that I'm going to be teaching you, but you can do onclick. And then in here we can use JavaScript to confirm and to have a pop up box that confirms whether or not the user wants to perform this action. So it'll say return confirm and then are you sure.

And then semi-colon at the end so that's just a little bit of JavaScript it's an onclick action. Now let's go back and reload our page we'll go to sample subject edit subject delete subject are you sure. See we get that pop-up we hit cancel then we don't do it. It's just a little extra protection. If we say yes, now it's gone, just like that. There's one last thing that I want us to take care of. You may have noticed that if we were to delete About Widget Corp, we would have a problem. And that's because there are pages that reference that subject, pages which are related to it. That is Our Mission and Our History.

What should happen to those pages when the subject is deleted? In most cases, we probably would not want to have orphaned pages in our database that don't have a subject to belong to. So then we have to make a choice. Do we want to delete these pages automatically whenever their related subject is deleted? Or do we want to disallow deleting a subject until all of the pages below it have been deleted first. I'm going to choose the second one and disallow it. And that'll force the user to remove the pages first. It may not be as convenient but it is the safer option that ensures that we don't delete too much accidentally. Either one is a perfectly valid choice though you could either have it happen automatically or force the user to manually.

Step through each one of those. So let's add that real quick to our delete_subject.php page. Now the place that we want to do this is right after we find the current subject. But before we actually perform the delete. So what we're going to do is pages_set equals and then we know how to find pages for a subject because we wrote a function for it earlier. Right, find_pages_for_subject. And then we just need to pass in a subject ID. Well, let's grab it from right here.

Current subject ID, we'll just paste that out. So that will then return, a page set to us. So it's mysqli_num_rows, or pages set is greater than 0, then we'll know that there are pages left, right? If we count the rows that were returned and it's greater than zero then we know we have some. So what do we want to do in that case? Well, let's just go down here and let's grab our failure message and our redirect, and let's paste those up here.

But instead of saying subject deleted failed, we want to say "Can't delete a subject with pages". That'll be our message and then we'll redirect them to this page. But, we don't have ID yet. ID is something that gets set here. Instead, we just still have current subject ID. So, we'll have to use that there instead. Alright, let's make sure I've got my semicolons all right. Alright, let's test it out. And remember that this redirect_to function will halt execution of the rest of the page.

Because it contains an exit after it sets the headers to the new location. So that will stop it from actually performing the deletion. And just do a redirect instead. So let's try it. Let's go here. Let's just try services. Edit subject. Delete subject. Are we sure? Yes, we are. Nope, can't delete a subject with pages. So now we get our error message instead. So this is an important point. When you have records that are relying on the presence of another record, for example, a parent record like with our subject. Then you will have to decide what you want to do with the dependent records if the parent record gets deleted. So that's all there is to subject deleting.

We've now seen all four types of CRUD. Create, read, update and delete. We've been able to apply them in our application to our subjects.

Find answers to the most frequently asked questions about PHP with MySQL Essential Training .

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Q: This course was revised on 6/4/2013. What changed?
A: The old version of this course was 6 years old and it was time for a complete revision, using PHP 5.4. (The tutorials will work with any version of PHP and covers any differences you might encounter). The author has also added updated installation instructions for Mac OS X Mountain Lion and Windows 8. The topics and end project are the same, but the code is slightly different. It also addresses frequently asked questions from the previous version.
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