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Detecting form submissions

From: PHP with MySQL Essential Training

Video: Detecting form submissions

In the previous movie, we learned to create and retreive the values from a web form, but we ran into an issue. When the form was submitted, our page worked just fine. But if the URL was loaded directly, instead of being submitted by the form, then the key values that our code was expecting to be in the post array weren't there. In this movie, we're going to talk about how you can detect whether or not a form has been submitted, so that you can handle this case appropriately. So, the problem that we have is that we're looking for this key, username, and it's not there. It doesn't exist in the post array, because the form wasn't posted. So therefore, it doesn't exist, and we're getting an error when we try and access it.

Detecting form submissions

In the previous movie, we learned to create and retreive the values from a web form, but we ran into an issue. When the form was submitted, our page worked just fine. But if the URL was loaded directly, instead of being submitted by the form, then the key values that our code was expecting to be in the post array weren't there. In this movie, we're going to talk about how you can detect whether or not a form has been submitted, so that you can handle this case appropriately. So, the problem that we have is that we're looking for this key, username, and it's not there. It doesn't exist in the post array, because the form wasn't posted. So therefore, it doesn't exist, and we're getting an error when we try and access it.

One simple solution to this would be to use is set. We remember how to do that, so we could do something like this. We could say if and then is set, no spaces. Dollar sign post and then username. So if that is set, then set username. And we can do the same thing for password. So now if we go back and try our page, we're just going to load it directly by hitting return and we still come up with an error. Why are we getting the error this time well this time it's different. This time it's undefined variable. That's because here we're trying to use it but if it's not set. Well this value doesn't get set so now this doesn't exist. So we solved one problem and created another problem at the same time. So we could do else dollar sign user name equals, and then let's do the same thing down here, else dollar sign password equals.

Now let's go back and load up our page this time, and now we've solved both problems. We're still getting this stray colon output, because it's outputting blank string, followed by a colon and a space, and then a blank string. But we've gotten rid of the errors by doing this. But we've written a whole lot of code here, just to handle this. Now, this incidentally is a good way to set default values. I'm going to go ahead and make a note here that default values. Because if you needed a default value for something, this is a good way to do it, to say If it's set, then set it to that value. If it's not set, set it to your default, and you would just provide the default value here. It doesn't have to be empty.

It could be my default value is Kevin. Maybe if you have a form that has a country field, you want to default to your current country, the United states or Canada or something like that. Now, If you do decide to go this way, I just want to show you that there is a better way to do that, and that is by using the ternary operator. Let me just close the PHP tags here. There we go. And let's open a new one. And now those are separated. And let me just show you what a ternary operator looks like. We didn't talk about this back when we talked about if statements, conditionals. It's just a special format for doing the if statements, and it has a Boolean test, followed by a question mark, then the value if the test is true. Then a colon and then the value of the test is false. So, you can see that this is a lot more efficient than writing all of this, but it does the exact same thing.

So, it's just a more compact way of writing it. If this is set, then set it to this, if not, set it to that. So, I want you to see that because that's a little more efficient. I think, a nicer way to do that. But, I think there's an even better way to do it than that, in this case. A way to detect whether the form has been submitted or not. And the way to do that, will put an if statement, is set. Just like we just did. And we'll look in that post array. But were going to look for submit. And then, for now, let's just do echo, form was submitted.

So, what we're doing here. Let's go back and remind ourselves what that looks like. Let's go to the form, and let's submit it. I'll click submit. Notice that there's this other value here called submit. Doesn't matter what all of the form is. I have something here called submit. And that's what I'm checking. Form was submitted. So it did, in fact, say that it was submitted. If I come here, and I do it this way. Now the form was not submitted. All of my default values also kicked in. That's beside the point. The thing that I want you to see is that this form was submitted whether it shows or not. So what's required to make this work is this.

Name equals and then something. I just use submit, that's the easiest thing. But you need to have some name attribute there. because that's going to make sure that in any time that the submit button is clicked, it's value is included in that array. If we take that away. Let's try that. Let's go back and we'll reload this page. And I'll just type in Kevin, password and Submit. Now it's not there. So that's the key thing. You have to have this name equal submit for this trick to work. So what does that gain me? Why do I want to do that? Well now, I have one way to check right off the bat whether or not this has been submitted.

Before I do any of these other tests, I can take all of these. Let me just cut it and let's paste it in here, and the ternary one. I'll go ahead and grab as well, just so that they're all together, and get rid of that. Okay? You see the difference? So now It's going to check and see whether the form was submitted, and if it is, it's going to do all of this processing. If not, it skips right past it. Now, it'll give me an error if I try and load this, because this is outside of that, and I don't have a value for username and password if I skip everything.

But I could easily fix that. Else and then set the default values here, username equals and password equals. That will then work just fine. Let's come back over here, form processing, reload the page, none of that takes place, these are the values that kick in. And if you want to prove to yourself you can put in Bob here Lets just reload the page you see that's the value being set. So this checks to see whether not post variables submit a set. And then we know it was posted to us. If it wasn't then it's a get request then we can handle the page differently based on whether it's a get request or a post request.

What's nice about this, is that instead of using two pages to do our form submission. One that has the form and one that receives the form, we can actually use a single page to both have our form and perform our form processing. Let's look at that next.

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This video is part of

Image for PHP with MySQL Essential Training
PHP with MySQL Essential Training

131 video lessons · 32803 viewers

Kevin Skoglund
Author

 
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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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