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Validating Dates

5:13 with Alena Holligan

How do we assure that the date is in the correct format and is actually a valid date? In this video, we'll explore one option for validating string formats and checking for a valid date.

Documentation

explode() Split a string by string

strlen() Get string length

checkdate() Validate a Gregorian date

Regular Expressions

Another option you often see for validating strings, is the use of regular expressions. A regular expression (regex or regexp for short) is a special text string for describing a search pattern. Regular expressions are a great tool to learn. Most applications as well as most programming languages include some form of regular expression matching.

PHP includes a number of Regular Expression Functions. We could use preg_match to match our dates as well.

Example:

if (preg_match('/^(\d{2})\/(\d{2})\/(\d{4})$/', $date, $dateMatch)) {
   if (!checkdate($dateMatch[1], $dateMatch[2], $dateMatch[3])) {
       $error_message = 'Invalid Date';
   }
} else {
   $error_message = 'Invalid Date format';
}

This matches a string that starts with (^) 2 digits (\d{2}), followed by a forward slash (\/), then another 2 digits (\d{2}) followed by another forward slash (\/), and finally 4 digits (\d{4}) at the end($).

The task form is working and adding values to the database but 0:00
we don't have any data integrity when it comes to dates. 0:04
The project is a drop down and the filtering for integer ensures 0:07
that the time is a number but currently we except anything in the date field. 0:11
We have suggested the format we want, a two-digit month 0:16
followed by a forward slash and a two digit day then another forward slash and 0:21
a four digit year but there's nothing enforcing that format. 0:26
So it's all too easy to add an invalid format whether we're trying to or 0:30
not or even an invalid date. 0:34
Not all months have 31 days. 0:37
So, how do we sure that the date is in the correct format and 0:39
is actually a valid date? 0:43
Let's jump back into work spaces and explore one option. 0:45
In task.php, after we've collected the user data, let's check the date variable. 0:49
First, we need to get each piece of the date so we'll use the explode function. 0:56
Explode takes two parameters, a string delimiter and the string and 1:01
returns an array. 1:06
So let's assign this to a variable dateMatch. 1:07
We use explode, And first the string delimiter. 1:13
The string delimiter determines where the string is split. 1:18
In the case of the date, we're going to use the forward slash 1:22
since each piece of the date should be separated with a forward slash. 1:25
Next we use the date for the string. 1:30
Now let's var dump the dateMatch. 1:35
This will show us what we have so far. 1:43
Now, let's go back to the browser. 1:45
Let's start with the completely invalid date and just type today. 1:48
When we submit the form, we see that the date match is set to a single item array 1:53
with the entire string as the first element. 1:58
Now, let's change this to put in a valid date that's just in the wrong format. 2:02
This is a valid date but not the format we want. 2:11
Now we see that dateMatch is a three item array 2:15
with each piece of the date as a separate element. 2:18
Excellent, just what we want. 2:22
Now, let's start writing the conditional. 2:24
Let's add an elseif to this conditional. 2:27
Elseif count dateMatch does not = 3. 2:38
Then we're going to set our error_message. 2:43
Invalid Date. 2:50
We also want to give this error if the date is not the correct format. 2:53
So, let's check that each piece of the array is the correct link. 2:58
Or, string length. 3:00
DateMatch 0. 3:09
Meaning, our first element is not = to 2 or 3:11
the string length, DateMatch 1. 3:16
Meaning, our second element is not = to 2 and 3:22
also string length, dateMatch 2. 3:28
Our third element is not = to 4. 3:34
And finally, we want to check that the date is actually valid and 3:38
that the user has not entered the day that does not exist. 3:42
For example, day 31 in a month that only has 30 days. 3:46
We can use the checkdate function for this or not checkdate. 3:50
checkdate takes three parameters. 3:58
First the month which is our dateMatch 0. 4:01
And then the day, dateMatch 1 and 4:05
then the year, dateMatch 2. 4:10
Great job. Let's take out the var dump and 4:17
run some tests in the browser. 4:18
When we refresh the page, we see our error for 4:25
the required fields because we check for that first. 4:28
So let's make sure all the fields are filled in. 4:32
Now we see invalid date because the year only has two characters and not four. 4:40
Let's change this to 9/31. 4:46
2016. 4:49
We still see invalid date because 4:52
September does not have 31 days. 4:57
Now let's change this to 8/31. 5:03
This time our date was added because the date is valid, great job. 5:06

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