Using PHP – Arrays, Databases and programming
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Transcript Using PHP – Arrays, Databases and programming
PHP (2) –
Functions, Arrays,
Databases, email and
sessions
Location of User defined PHP
functions
Where can PHP Functions be located ?
The short answer is: Anywhere!
Before the <head> section.
In the <head> ... </head> section.
In the <body> ... </body> section
PHP
Function
Location
The output of the previous
slide
External PHP Functions
Can we put PHP functions in external
files and load them into pages ? - Yes !
When a website gets beyond a few
pages in size, then it is most convenient
to put the PHP functions in one or more
external files. This also facilitates the
maintenance and upgrading of the site
Example of external PHP
function file
Result of interpreting the php file
on the previous page
Returning Values from
functions
PHP functions can return a value – note that
returning a value from a function is optional.
The syntax for returning a single value is
fairly straightforward – you just use the
return keyword followed by the variable or
value you want to return from the function.
PHP functions can also return nothing at all.
i.e a function doesn’t have to use the return
keyword at all or it can use return and not
have a variable or value after it.
Example function returning a
value
Result of interpreting the code
in the previous slide
PHP Arrays
An array in PHP is a list of key/value elements in
which any number of values can be stored
(provided there is enough memory available).
There are 2 types of arrays in PHP – indexed and
associative
Indexed arrays are the ones most people are
familiar with. The key (or index) to each value is an
integer.
Associative arrays can be useful at times. Members
of associative arrays are accessed by means of text
strings. The key (or index) to each value is a string.
When working with arrays in PHP, there is
frequently more than one way of accomplishing a
task.
Creating
Indexed
Arrays
and the
scope of
loops
The result of accessing the
previous page
Creating Associative Arrays
Accessing the elements of an
Associative Array
Elements can be accessed easily by
means of their key.
If you want to access each element
in sequence there are a number of
approaches.
One simple approach is to use the
each() function.
Using each() and reset()
The result of running the
previous page.
The foreach() function
This is similar to the each() function, but it
incorporates a loop and traverses the whole
array it is applied to.
The foreach() function takes two arguments.
The first argument is the name of the array
to be traversed. The second argument is the
name of the variable to hold the individual
element.
The foreach() function can be applied to
multidimensional arrays and associative
arrays as well as indexed arrays.
Using
the
foreach()
function
The result of accessing the
previous page
PHP functions supporting MYSQL
operations
PHP has a large number of functions
that enable it to interact with mysql
databases.
This includes functions to open and
close connections with databases, pass
SQL queries to MYSQL tables, and
process the results of queries.
The results of MYSQL queries in PHP
can usually be treated as an array
PHP and MySQL (2)
PHP functions that interact with MySQL may be
classified into groups. These are shown in the table
below:-
Connecting and Disconnecting to
MySQL Databases using PHP
Define a PHP constant by using
the define() function
The PHP define() function enables PHP
programmers to create named data
items whose value cannot be changed.
Once a constant is defined, it can
never be changed or undefined in
the script.
Using the define() function
Creating and dropping
databases in PHP
There are 2 functions in this group. These
are mysql_create_db and mysql_drop_db.
These functions would normally only be used
by the administrator of an e-commerce
website.
The power to create and destroy tables is not
something that outside users of e-commerce
sites should be allowed to do. There are very
severe security considerations associated
with these commands.
MySQL Access Privileges
In MySQL (and most other serious database
systems) it is possible to set different access
levels for different users.
Access privileges for MySQl include select (i.e.
query), insert, update, delete, create, drop,
reload and many others.
Casual users of database systems (e.g. the
user “potiro” in the poti database system)
are normally only given the “select” privilege.
This means that they can only read tables
using the “select” statement.
Performing MySQL queries
using PHP
MySQL Queries
As outlined last week, MySQL groups data into
databases. Each database consists of one or
more tables. It is the tables that actually contain
useful data.
An example database is the poti database on the
MySQL server on sally.
The user “potiro” has access to the mysql server
on sally.
Rather than having unrestricted access to all
databases on the mysql server on sally, the user
potiro only has access to the database poti. This
access is further restricted to read access only.
That is, the user potiro can only read tables in
the database poti.
MySQL Select Query example
Consider a table called “books” in a
database called “wea”. The table has the
structure outlined below:-
To run a query that selects all columns of all rows in the
table books that have the author_lastname column equal to
“Barrow” we can either run a select command interactively or
use the PHP mysql_query command.
Contents of books table
A form driven query can be constructed to
search the table
Searchbooks.php
The result of running the
previous slide
Accessing the array $a_row as
an indexed array
We can also treat each row of the output of the
mysql query as an indexed array.
The best alternative for handling
the output – an associative array
As shown on the previous slides,
processing the result of mysql_query
using an indexed array works quite well.
However, processing the result of the
query as an associative array gives us a
lot more flexibility.
Processing the results
associative array
If we treat the results of mysql_query
as an associative array, we actually
have a lot more freedom with what we
can do.
For example, we can alter the order in
which the columns are printed out. We
can also ignore some columns if we
wish.
Processing the results
associative array (2)
Processing the results
associative array (3)
PHP functions returning other
information about MySQL
Example usage of
mysql_list_dbs()
Output of the previous slide
Sending email from PHP
PHP can send email.
The function to do this is called mail()
Understanding Sessions
To use sessions we need to bring
together a number of concepts that we
have already looked at in this course.
These are : Forms – getting and posting
data
Arrays : Associative and indexed
Server $_GET,$_POST and $_REQUEST
arrays, also the $_SESSION array.
PHP Sessions
PHP Sessions
are a way of
storing
persistent
data, created
in one web
page, on the
server so it
can be
accessed by
multiple web
pages.
Example Session
The next few pages show some example php
and HTML for creating a session and storing
two variables “products[]” (an array) and
“pos” an integer giving the index number of
the next available position in the array.
All 3 pages (setup.php, view.php and
unreg.php) begin with a call to
session_start()
setup.php is used to create the session
initially, view.php is used to view the stored
data and unreg.php is used to end the
session and destroy any stored data.
Session files structure
PHP Session – setup form
Running setup.php
Running setup.php
view.php
Running
view.php
Ending a session - unreg.php
Some more facts
about sessions
The session data is stored in a file that can only
be read by the user running the server (at least on
Unix systems this is the case)
Every session has a unique session id
The stored session data is stored in a special
format inside the file.
When the session_start() function is called the
file is created but is empty.
Calling session_unreg() deletes the session file
Yet more facts about
Sessions
Sessions normally use cookies to store the
session id on the client side.
The location of the session files is set by
the PHP configuration file (php.ini) which
uses the directive session.save_path to set it.
References:
Textbook (Meloni)
The php.net site has a lot of information about
sessions and MySQL . See
http://au2.php.net/session and
http://au2.php.net/mysql
There is a good discussion of sessions at
http://www.oreilly.com/catalog/webdbapps/ch
apter/ch08.html
In addition, a search on Google will bring up
many other websites.