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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($).

  • 0:00

    The task form is working and adding values to the database but

  • 0:04

    we don't have any data integrity when it comes to dates.

  • 0:07

    The project is a drop down and the filtering for integer ensures

  • 0:11

    that the time is a number but currently we except anything in the date field.

  • 0:16

    We have suggested the format we want, a two-digit month

  • 0:21

    followed by a forward slash and a two digit day then another forward slash and

  • 0:26

    a four digit year but there's nothing enforcing that format.

  • 0:30

    So it's all too easy to add an invalid format whether we're trying to or

  • 0:34

    not or even an invalid date.

  • 0:37

    Not all months have 31 days.

  • 0:39

    So, how do we sure that the date is in the correct format and

  • 0:43

    is actually a valid date?

  • 0:45

    Let's jump back into work spaces and explore one option.

  • 0:49

    In task.php, after we've collected the user data, let's check the date variable.

  • 0:56

    First, we need to get each piece of the date so we'll use the explode function.

  • 1:01

    Explode takes two parameters, a string delimiter and the string and

  • 1:06

    returns an array.

  • 1:07

    So let's assign this to a variable dateMatch.

  • 1:13

    We use explode, And first the string delimiter.

  • 1:18

    The string delimiter determines where the string is split.

  • 1:22

    In the case of the date, we're going to use the forward slash

  • 1:25

    since each piece of the date should be separated with a forward slash.

  • 1:30

    Next we use the date for the string.

  • 1:35

    Now let's var dump the dateMatch.

  • 1:43

    This will show us what we have so far.

  • 1:45

    Now, let's go back to the browser.

  • 1:48

    Let's start with the completely invalid date and just type today.

  • 1:53

    When we submit the form, we see that the date match is set to a single item array

  • 1:58

    with the entire string as the first element.

  • 2:02

    Now, let's change this to put in a valid date that's just in the wrong format.

  • 2:11

    This is a valid date but not the format we want.

  • 2:15

    Now we see that dateMatch is a three item array

  • 2:18

    with each piece of the date as a separate element.

  • 2:22

    Excellent, just what we want.

  • 2:24

    Now, let's start writing the conditional.

  • 2:27

    Let's add an elseif to this conditional.

  • 2:38

    Elseif count dateMatch does not = 3.

  • 2:43

    Then we're going to set our error_message.

  • 2:50

    Invalid Date.

  • 2:53

    We also want to give this error if the date is not the correct format.

  • 2:58

    So, let's check that each piece of the array is the correct link.

  • 3:00

    Or, string length.

  • 3:09

    DateMatch 0.

  • 3:11

    Meaning, our first element is not = to 2 or

  • 3:16

    the string length, DateMatch 1.

  • 3:22

    Meaning, our second element is not = to 2 and

  • 3:28

    also string length, dateMatch 2.

  • 3:34

    Our third element is not = to 4.

  • 3:38

    And finally, we want to check that the date is actually valid and

  • 3:42

    that the user has not entered the day that does not exist.

  • 3:46

    For example, day 31 in a month that only has 30 days.

  • 3:50

    We can use the checkdate function for this or not checkdate.

  • 3:58

    checkdate takes three parameters.

  • 4:01

    First the month which is our dateMatch 0.

  • 4:05

    And then the day, dateMatch 1 and

  • 4:10

    then the year, dateMatch 2.

  • 4:17

    Great job. Let's take out the var dump and

  • 4:18

    run some tests in the browser.

  • 4:25

    When we refresh the page, we see our error for

  • 4:28

    the required fields because we check for that first.

  • 4:32

    So let's make sure all the fields are filled in.

  • 4:40

    Now we see invalid date because the year only has two characters and not four.

  • 4:46

    Let's change this to 9/31.

  • 4:49

    2016.

  • 4:52

    We still see invalid date because

  • 4:57

    September does not have 31 days.

  • 5:03

    Now let's change this to 8/31.

  • 5:06

    This time our date was added because the date is valid, great job.

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