CodeIgniter – Basic Concepts
CodeIgniter – Basic Concepts
Controllers
A controller
is
a simple
class
file.
As
the
name suggests,
it
controls
the
whole
application by URI.
Creating a Controller
First,
go
to
application/controllers folder.
You
will
find
two
files
there,
index.html
and Welcome.php. These files come with the CodeIgniter.
Keep
these
files
as
they
are.
Create
a
new
file
under
the
same
path
named
“Test.php”.
Write the following code in that file:
<?php
class Test
extends
CI_Controller
{
public function
index()
{
echo "Hello
World!";
}
}
?>
The Test class extends an in-built class called CI_Controller. This class must be extended whenever you want to make your own Controller class.
Calling a Controller
The above controller can be called by URI as follows:
Notice
the word
“test”
in
the above URI
after index.php. This indicates the class name of controller. As
we
have
given
the
name
of
the
controller
“Test”,
we
are
writing
“test” after
the
index.php.
The
class
name
must
start
with
uppercase letter but
we
need
to write
lowercase letter when
we
call
that
controller
by
URI.
The
general
syntax
for calling the controller is as follows:
http://www.your-domain.com/index.php/controller/method-name
Creating & Calling Constructor Method
Let us modify
the above class
and create
another method
named
“hello”.
<?php
class Test
extends
CI_Controller
{
public function
index()
{
echo "This
is
default
function.";
}
public function
hello()
{
echo "This
is
hello
function.";
}
}
?>
We can execute the above controller in the following three ways:
After
visiting
the
first
URI
in
the
browser,
we
get
the
output
as
shown
in
the
picture given
below.
As
you
can
see,
we
got
the
output
of
the
method
“index”,
even
though
we did
not
pass
the
name
of
the
method
the
URI.
We
have
used
only
controller
name
in
the URI. In such situations, the CodeIgniter calls the
default method “index”.
Visiting
the
second
URI
in
the
browser,
we
get
the
same
output
as
shown
in
the
above picture.
Here,
we
have
passed
method’s
name
after
controller’s
name
in
the
URI.
As
the name
of
the method
is
“index”,
we
are
getting the
same output.
Visiting the
third
URI in
the
browser,
we
get
the
output
as
shown
in
picture
given
below. As
you
can
see,
we
are
getting
the
output of the method “hello” because we have passed “hello”
as
the method name, after
the
name of
the controller
“test”
in the
URI.
Points to Remember:
·The name of the controller class must start with
an uppercase letter.
·The controller must be called with lowercase letter.
·Do not
use
the
same
name
of
the
method
as
your
parent
class,
as
it
will
override
parent class’s functionality.
Views
This can
be
a simple
or
complex webpage,
which
can
be
called
by
the controller.
The webpage
may
contain
header,
footer,
sidebar
etc.
View
cannot
be
called
directly.
Let
us
create
a simple view. Create
a new file under
application/views with
name
“test.php”
and copy the below given code in that file.
<!DOCTYPE
html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>CodeIgniter
View
Example</title>
</head>
<body>
CodeIgniter
View
Example
</body>
</html>
Change the code of application/controllers/test.php file as shown in the below.
Loading the View
The view can be loaded by the following syntax:
$this->load->view('name');
Where name is the view file, which is being rendered. If you have planned to store the view file in some directory then you can use the following syntax:
$this->load->view('directory-name/name');
It
is
not
necessary
to
specify
the
extension
as
php,
unless
something
other
than
.php
is used.
The
index()
method
is
calling
the
view
method
and
passing
the
“test”
as
argument
to
view() method because we have stored the html coding in “test.php” file under application/views/test.php.
<?php
class Test
extends
CI_Controller
{
public function
index()
{
$this->load->view('test');
}
}
?>
Here is the output of the above code:
Models
Models
classes
are
designed
to
work
with
information
in
the
database.
As
an
example,
if you
are
using
CodeIgniter
to
manage
users
in
your
application
then
you
must
have model
class,
which
contains
functions
to
insert,
delete,
update
and
retrieve
your
users’
data.
Creating Model Class
Model classes are stored in
application/models directory. Following code shows how to create model class in CodeIgniter.
<?php
Class Model_name
extends
CI_Model{
Public function
construct()
{
parent:: construct();
}
}
?>
Where
Model_name
is
the
name
of
the
model
class
that
you
want
to
give.
Each
model class
must
inherit
the
CodeIgniter’s
CI_Model
class. The
first letter
of the
model
class must be in capital
letter.
Following
is
the
code for
users’
model
class.
<?php
Class zzzextends
CI_Model{
Public function
construct()
{
parent:: construct();
}
}
?>
The above model
class must be saved as User_model.php. The class name and file name must be same.
Loading Model
Model can be called in controller. Following code can be used to load any model.
$this->load->model('model_name');
Where
model_name
is
the
name
of
the
model
to
be
loaded.
After
loading
the
model
you can simply call its method as shown below.
$this->model_name->method();
Auto-loading Models
There
may
be
situations
where
you
want
some
model
class
throughout
your
application. In such situations, it is better if we autoload it.
As shown
in
the
above
figure,
pass
the
name
of
the
model
in
the
array
that
you
want
to autoload
and it
will
be
autoloaded,
while
system
is in initialization
state
and
is
accessible throughout the application.
Helpers
As the name suggests, it will help you build your system. It is divided into small functions to serve different functionality. A number of helpers are available in CodeIgniter, which are listed in the table below. We can build our own helpers too.
Helpers are typically stored in your system/helpers, or application/helpers directory.
Custom
helpers
are
stored
in
application/helpers directory
and systems’
helpers are stored in system/helpers directory. CodeIgniter will look first in your application/helpers directory.
If the directory does not exist or the specified helper is not
located,
CodeIgniter
will
instead,
look
in
your
global
system/helpers/ directory. Each helper, whether it is custom or system helper, must be loaded before using it.
Loading a Helper
A helper can be loaded as shown below:
$this->load->helper('name');
Where name is the name of the helper. For example, if you want to load the URL Helper, then it can be loaded as:
$this->load->helper('url');
Routing
CodeIgniter
has
user-friendly
URI
routing
system,
so
that
you
can
easily
re-route
URL. Typically,
there
is
a
one-to-one
relationship
between
a
URL
string
and
its
corresponding controller class/method. The segments in a URI normally follow this pattern:
your-domain.com/class/method/id/
·The first segment represents the controller class that should be invoked.
·The
second segment represents
the
class
function,
or
method,
that
should
be called.
·The
third,
and
any
additional
segments,
represent
the
ID
and
any
variables
that will be passed to the controller.
In some situations, you may want to change this default routing mechanism. CodeIgniter provides facility through which you can set your own routing rules.
Customize Routing Rules
There is a particular file where you can handle all these. The file is located at application/config/routes.php. You will find an array called $route in which you can customize
your
routing
rules.
The
key
in
the
$route
array
will
decide
what
to
route
and the value will decide where to route. There are three reserved routes in CodeIgniter.
Routes
can
be
customized
by
wildcards or
by
using
regular expressions but
keep
in mind that these customized rules for routing must come after the reserved rules.
Wildcards
We can use two wildcard characters as explained below:
·(:num) – It will match a segment containing only numbers.
·(:any) – It will match a segment containing any character.
Example
In
the
above
example,
if
the
literal
word
“product”
is
found
in
the
first
segment
of
the
URL, and a number is found in the second segment, the “catalog” class and the
“product_lookup”
method are
used instead.
Regular Expressions
Like
wildcards,
we
can
also
use
regular
expressions in
$route array key part.
If any URI matches
with
regular
expression,
then
it
will
be
routed
to
the
value
part
set
into
$route array.
Example
$route['products/([a-z]+)/(\d+)']='$1/id_$2';
In the above example, a URI similar to products/shoes/123 would instead call the
“shoes” controller class and the “id_123”
method.
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