php-and-mysql

Getting Started
Basics
Arrays
Loop/Branch
Functions
OOP
Libraries
Files
MySQL
SQL
PHP/MySQL
Regex
Email
Date/Time
Web
Forms

Working with Date and Time

Understanding Timestamps
Using the "date" Command
Using the DateTime Class
Performing Date Arithmetic
LAB: Capturing Date of Birth Using DateTime

Understanding Timestamps

What is a timestamp?

The timestamp comes from UNIX and represents the number of seconds since midnight, 1 January 1970 GMT
When would you use a timestamp?

Timestamps are often used to store date and time information in a database
How can you get a timestamp using PHP?

Use the "time()", "mktime()" or "strtotime()" commands
What are some "relative" formats?

Relative formats include day names, numbers, ordinality (e.g. first, third),
relative (e.g. next, last) and units (e.g. hour, day, month)

Using the "date" Command

What is the "date" command?

The date() command is used to generate a date in the form of a string from a timestamp
When would you use the "date" command?

The date() command is used to display dates for the benefit of website users
What is a date format string?

The date format string is much like a format string when using printf().
There are format letters which represent parts of a date or time
What are some of the more common date formats?

Y = 4 digit year, m = 2 digit month, d = 2 digit day
H = 24 hour, i = minutes, s = seconds

Using the DateTime Class

What is the DateTime class?

The DateTime class is a standard PHP extension
and encompasses the various time commands into a single class
When would you want to use the DateTime class instead of the "date" command?

The DateTime class is useful when using Object Oriented Programming.
This class also lets you do date arithmetic without having to calculate minutes, hours, days, weeks, etc.
How do you use the DateTime class?

$date = new DateTime()
Optionally $date = new DateTime("date_string")
or $date->setTimestamp(timestamp)
How can you capture date information in a web form?

Have separate fields for year, month, day, etc.

Performing Date Arithmetic

What is "date arithmetic"?

Date arithmetic is the process of adding or subtracting time periods to or from a given date
How can you determine a date knowing how many
days, weeks or months you need to add or subtract?

The easiest way is to use the DateInterval and DateTime classes
How can date arithmetic help with a website?

Date arithmetic is useful when you need figure out the exact date
only knowing how many days or weeks into the future or past
How can you determine the day of week from a date?

1. Build the timestamp which represents the date
2. date("l", $timestamp)

LAB: Capturing Date of Birth Using DateTime

What is the purpose of this lab?
- In this lab you will learn how to handle a birthdate.
- The date will be entered when a new member signs up.
- In the lab you will use DateTime to validate the date
- Using DateTime arithmetic you will detect if the new member is under age 21
Modify sweetscomplete/addmember.php ...
- From your editor open sweetscomplete/addmember.php
- Add a three fields:
  - Day should be a drop down list from 1 to 31
  - Month should be a drop down list with the months
  - Year should be a drop down list from this year to this year - 120
  - HINT: use a "for()" loop, arrays, and the "range()" function to produce the lists
Use DateTime to validate the date ...
- Build a DateTime object from the three fields
- Use try { xxx; } catch() { xxx } to capture any errors
- If an exception is thrown assume the information given was invalid
- Using date arithmetic generate an error if the birthdate indicates an age under 21
Test in the browser ...
- From your browser open http://localhost/sweetscomplete/addmember.php
- Try entering 2001-02-31

+ o -