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ExpressionEngine

2.9.0 User Guide

General Style and Syntax

File Format

Files should be saved with Unicode (UTF-8) encoding. The BOM should not be used. Unlike UTF-16 and UTF-32, there’s no byte order to indicate in a UTF-8 encoded file, and the BOM can have a negative side effect in PHP of sending output, preventing the application from being able to set its own headers. Unix line endings should be used (LF).

Here is how to apply these settings in some of the more common text editors. Instructions for your text editor may vary; check your text editor’s documentation.

TextMate

  1. Open the Application Preferences
  2. Click Advanced, and then the “Saving” tab
  3. In “File Encoding”, select “UTF-8 (recommended)”
  4. In “Line Endings”, select “LF (recommended)”
  5. Optional: Check “Use for existing files as well” if you wish to modify the line endings of files you open to your new preference.

BBEdit

  1. Open the Application Preferences
  2. Select “Text Encodings” on the left.
  3. In “Default text encoding for new documents”, select “Unicode (UTF-8, no BOM)”
  4. Optional: In “If file’s encoding can’t be guessed, use”, select “Unicode (UTF-8, no BOM)”
  5. Select “Text Files” on the left.
  6. In “Default line breaks”, select “Mac OS X and Unix (LF)”

PHP Closing Tag

The PHP closing tag on a PHP document ?> is optional to the PHP parser. However, if used, any whitespace following the closing tag, whether introduced by the developer, user, or an FTP application, can cause unwanted output, PHP errors, or if the latter are suppressed, blank pages. For this reason, all PHP files should OMIT the closing PHP tag, and instead use a comment block to mark the end of file and it’s location relative to the application root. This allows you to still identify a file as being complete and not truncated.

INCORRECT:

<?php
    echo "Here's my code!";
?>

CORRECT:

<?php
    echo "Here's my code!";

/* End of file myfile.php */
/* Location: ./system/expressionengine/thirs_party/mymodule/myfile.php */

Class and Method Naming

Class names should always have their first letter uppercase, and the constructor method should use __construct(). Multiple words should be separated with an underscore, and not CamelCased. All other class methods should be entirely lowercased and named to clearly indicate their function, preferably including a verb. Try to avoid overly long and verbose names.

INCORRECT:

class superclass
class SuperClass

CORRECT:

class Super_class

Example of an improper and proper constructor method:

INCORRECT:

class Super_class {
    function Super_class()      // does not use __construct()
    {
    }
}

CORRECT:

class Super_class {
    function __construct()
    {
    }
}

Examples of improper and proper method naming:

INCORRECT:

function fileproperties()       // not descriptive and needs underscore separator
function fileProperties()       // not descriptive and uses CamelCase
function getfileproperties()    // Better!  But still missing underscore separator
function getFileProperties()    // uses CamelCase
function get_the_file_properties_from_the_file()  // wordy

CORRECT:

function get_file_properties()  // descriptive, underscore separator, and all lowercase letters

Variable Names

The guidelines for variable naming is very similar to that used for class methods. Namely, variables should contain only lowercase letters, use underscore separators, and be reasonably named to indicate their purpose and contents. Very short, non-word variables should only be used as iterators in for() loops.

INCORRECT:

$j = 'foo';       // single letter variables should only be used in for() loops
$Str              // contains uppercase letters
$bufferedText     // uses CamelCasing, and could be shortened without losing semantic meaning
$groupid          // multiple words, needs underscore separator
$name_of_last_city_used // too long

CORRECT:

for ($j = 0; $j < 10; $j++)

$str
$buffer
$group_id
$last_city

Commenting

In general, code should be commented prolifically. It not only helps describe the flow and intent of the code for less experienced programmers, but can prove invaluable when returning to your own code months down the line. There is not a required format for comments, but the following are recommended.

DocBlock style comments preceding class and method declarations so they can be picked up by IDEs:

/**
* Super Class
*
* @package Package Name
* @subpackage  Subpackage
* @category    Category
* @author  Author Name
* @link    http://example.com
*/
class Super_class {

    /**
    * Encodes string for use in XML
    *
    * @access  public
    * @param   string
    * @return  string
    */
    function xml_encode($str)

Use single line comments within code, leaving a blank line between large comment blocks and code:

// break up the string by newlines
$parts = explode("\n", $str);

// A longer comment that needs to give greater detail on what is
// occurring and why can use multiple single-line comments.  Try to
// keep the width reasonable, around 70 characters is the easiest to
// read.  Don't hesitate to link to permanent external resources
// that may provide greater detail:
//
// http://example.com/information_about_something/in_particular/
$parts = $this->foo($parts);

Constants

Constants follow the same guidelines as do variables, except constants should always be fully uppercase. Always use ExpressionEngine constants when appropriate, i.e. ``LD``, ``RD``, ``PATH_CACHE``, etc.

INCORRECT:

myConstant  // missing underscore separator and not fully uppercase
N           // no single-letter constants
S_C_VER     // not descriptive
$str = str_replace('{foo}', 'bar', $str);   // should use LD and RD constants

CORRECT:

MY_CONSTANT
NEWLINE
SUPER_CLASS_VERSION
$str = str_replace(LD.'foo'.RD, 'bar', $str);

TRUE, FALSE, and NULL

TRUE, FALSE, and NULL keywords should always be fully uppercase.

INCORRECT:

if ($foo == true) $bar = false;
function foo($bar = null)

CORRECT:

if ($foo == TRUE) $bar = FALSE;
function foo($bar = NULL)

Logical Operators

Use of || is discouraged as its clarity on some output devices is low (looking like the number 11 for instance). && is preferred over AND but either are acceptable, and a space should always precede and follow !.

INCORRECT:

if ($foo || $bar)
if ($foo AND $bar)  // okay but not recommended for common syntax highlighting applications
if (!$foo)
if (! is_array($foo))

CORRECT:

if ($foo OR $bar)
if ($foo && $bar) // recommended
if ( ! $foo)
if ( ! is_array($foo))

Comparing Return Values and Typecasting

Some PHP functions return FALSE on failure, but may also have a valid return value of "" or 0, which would evaluate to FALSE in loose comparisons. Be explicit by comparing the variable type when using these return values in conditionals to ensure the return value is indeed what you expect, and not a value that has an equivalent loose- type evaluation.

Use the same stringency in returning and checking your own variables. Use === and !== as necessary.

INCORRECT:

// If 'foo' is at the beginning of the string, strpos will return a 0,
// resulting in this conditional evaluating as TRUE
if (strpos($str, 'foo') == FALSE)

CORRECT:

if (strpos($str, 'foo') === FALSE)

INCORRECT:

function build_string($str = "")
{
    if ($str == "")     // uh-oh!  What if FALSE or the integer 0 is passed as an argument?
    {
    }
}

CORRECT:

function build_string($str = "")
{
    if ($str === "")
    {
    }
}

See also information regarding typecasting, which can be quite useful. Typecasting has a slightly different effect which may be desirable. When casting a variable as a string, for instance, NULL and boolean FALSE variables become empty strings, 0 (and other numbers) become strings of digits, and boolean TRUE becomes "1":

$str = (string) $str; // cast $str as a string

Comparing Version Numbers

When comparing version numbers, whether it be for comparing MySQL versions for compatibility with a particular feature, or for comparing the installed version of a module with the current version, these comparisons should not be made with loose typing, or even assuming that the version number will be entirely numeric. Use version_compare() instead.

INCORRECT:

if ($current < '2.3.1')

CORRECT:

if (version_compare($current, '2.3.1', '<'))

One of the big advantages here is that this PHP function accounts for many standard version numbering schemes, including alpha and beta suffixes.

Setting Strings from Method Calls

Sometimes it is desirable when setting a string from a method call to initialize with an empty string if the method returns FALSE. For speed and code legibility, instead of a ternary operator or conditional, simply cast the return value as a string.

INCORRECT:

$foo = ($this->input->post('foo')) ? $this->input->post('foo') : '';

$bar = $this->some_method();
if ($bar === FALSE)
{
    $bar = '';
}

CORRECT:

$foo = (string) $this->input->post('foo');

$bar = (string) $this->some_method();

Debugging Code

No debugging code can be left in place for submitted add-ons unless it is commented out, i.e. no var_dump(), print_r(), die(), and exit() calls that were used while creating the add-on, unless they are commented out.

// print_r($foo);

Whitespace in Files

No whitespace can precede the opening PHP tag. ExpressionEngine output is buffered, so whitespace in your files can cause output to begin before ExpressionEngine outputs its content, leading to errors and an inability for ExpressionEngine to send proper headers.

Compatibility

Unless specifically mentioned in your add-on’s documentation, all code must be compatible with PHP version 5.3.10+. Additionally, do not use PHP functions that require non-default libraries to be installed unless your code contains an alternative method when the function is not available, or you explicitly document that your add-on requires said PHP libraries.

Use of ee()->session->cache

ee()->session->cache is an array provided for you to use for “flash” content, i.e. values that you would like to persist during a page load, helping you eliminate redundant queries and PHP processing. To avoid conflicts with other first and third-party use of this array, always access it as a multi-dimensional array, using your class name as the primary array name, and your variables within. Naming conventions should follow that of other variables: lowercase letters, underscores for separators between words, and meaningful names.

INCORRECT:

ee()->session->cache['admins']
ee()->session->cache['Super_class']['admins']

CORRECT:

ee()->session->cache['super_class']['admins']

Here is an example of how one might utilize the $EE->session->cache array. This way, no matter how many times this method is called on a given page load (for instance, a tag being used twice on a template, or within a tag that might loop, such as a plugin within the Channel entries tag), the query and loading of the array occurs only once:

if ( ! isset(ee()->session->cache['super_class']['admins']))
{
    $query = ee()->db->query("SELECT member_id FROM exp_super_class_admins");

    if ($query->num_rows()() > 0)
    {
        foreach($query->result_array() as $row)
        {
            ee()->session->cache['super_class']['admins'][] = $row['member_id'];
        }
    }
}  // set a local variable from the cached

You can see an example of real-world usage of $EE->session->cache in the Channel module’s fetch_custom_channel_fields() and next_prev_entry() methods, and the IP to Nation module’s get_country() method.

Class and File Names using Common Words

When your class or filename is a common word, or might quite likely be identically named in another PHP script, provide a unique prefix to help prevent collision. Always realize that your end users may be running other add-ons or third party PHP scripts. Choose a prefix that is unique to your identity as a developer or company.

INCORRECT:

class Email
pi.email.php
class Xml
ext.xml.php
clasimport_request_variables()_request_variables()rt
mod.import.php

CORRECT:

class Pre_email
pi.pre_email.php
class Pre_xml
ext.pre_xml.php
class Pre_import
mod.pre_import.php

Database Table Names

Any tables that your add-on might use must use the exp_ prefix, followed by a prefix uniquely identifying you as the developer or company, and then a short descriptive table name. You do not need to be concerned about the database prefix being used on the user’s installation, as ExpressionEngine’s database class will automatically convert exp_ to what is actually being used.

INCORRECT:

email_addresses     // missing both prefixe
pre_email_addresses // missing exp_ prefix
exp_email_addresses // missing unique prefix

CORRECT:

exp_pre_email_addresses

Note

Be mindful that MySQL has a limit of 64 characters for table names. This should not be an issue as table names that would exceed this would likely have unreasonable names. For instance, the following table name exceeds this limitation by one character. Silly, no:

exp_pre_email_addresses_of_registered_users_in_seattle_washington

One File per Class

Use separate files for each class your add-on uses, unless the classes are closely related. An example of ExpressionEngine files that contains multiple classes is the Database class file, which contains both the DB class and the DB_Cache class, and the Magpie plugin, which contains both the Magpie and Snoopy classes.

Whitespace

Use tabs for whitespace in your code, not spaces. This may seem like a small thing, but using tabs instead of whitespace allows the developer looking at your code to have indentation at levels that they prefer and customize in whatever application they use. And as a side benefit, it results in (slightly) more compact files, storing one tab character versus, say, four space characters.

Line Breaks

Files must be saved with Unix line breaks. This is more of an issue for developers who work in Windows, but in any case ensure that your text editor is setup to save files with Unix line breaks.

Code Indenting

Use Allman style indenting. With the exception of Class declarations, braces are always placed on a line by themselves, and indented at the same level as the control statement that “owns” them.

INCORRECT:

function foo($bar) {
    // ...
}

foreach ($arr as $key => $val) {
    // ...
}

if ($foo == $bar) {
    // ...
} else {
    // ...
}

for ($i = 0; $i < 10; $i++)
    {
    for ($j = 0; $j < 10; $j++)
        {
            // ...
        }
    }

CORRECT:

function foo($bar)
{
    // ...
}

foreach ($arr as $key => $val)
{
    // ...
}

if ($foo == $bar)
{
    // ...
}
else
{
    // ...
}

for ($i = 0; $i < 10; $i++)
{
    for ($j = 0; $j < 10; $j++)
    {
        // ...
    }
}

Bracket and Parenthetic Spacing

In general, parenthesis and brackets should not use any additional spaces. The exception is that a space should always follow PHP control structures that accept arguments with parenthesis (declare, do- while, elseif, for, foreach, if, switch, while), to help distinguish them from functions and increase readability:

INCORRECT: $arr[ $foo ] = 'foo';
CORRECT: $arr[$foo] = 'foo';     // no spaces around array keys

INCORRECT: function foo ( $bar )
CORRECT: function foo($bar)      // no spaces around parenthesis in function declarations

INCORRECT: foreach( $query->result_array() as $row )
CORRECT: foreach ($query->result_array() as $row)    // single space following PHP control structures, but not in interior parenthesis

Long Lines and Indentation

In cases where the line length is longer than 80 characters and the line includes method calls with multiple parameters, put individual parameters (including additional method calls) on separate lines:

return str_replace(
  $match[1],
  preg_replace(
    "#href=.*?(alert\(|alert&\#40;|javascript\:|livescript\:|mocha\:|charset\=|window\.|document\.|\.cookie|<script|<xss|base64\s*,)#si",
    "",
    $attributes
  ),
  $match[0]
);

Also note that long strings don’t need to be broken up and closing parenthesis always appear at the same indentation level as the opening parenthesis.

Localized Text in Control Panel

Any text that is output in the control panel should use language variables in your module’s lang file to allow localization:

INCORRECT: return "Invalid Selection";
CORRECT: return lang('invalid_selection');

Private Methods and Variables

Methods and variables that are only accessed internally by your class, such as utility and helper functions that your public methods use for code abstraction, should be prefixed with an underscore:

convert_text()        // public method
_convert_text()     // private method

PHP Errors

Code must run error free and not rely on warnings and notices to be hidden to meet this requirement. For instance, never access a variable that you did not set yourself (such as $_POST array keys) without first checking to see that it isset().

Make sure that while developing your add-on, error reporting is enabled for ALL users, and that display_errors is enabled in the PHP environment. You can check this setting with:

if (ini_get('display_errors') == 1)
{
  exit "Enabled";
}

On some servers where display_errors is disabled, and you do not have the ability to change this in the php.ini, you can often enable it with:

ini_set('display_errors', 1);

Note

Setting the display_errors setting with ini_set() at runtime is not identical to having it enabled in the PHP environment. Namely, it will not have any effect if the script has fatal errors

Short Open Tags

Always use full PHP opening tags, in case a server does not have short_open_tag enabled.

INCORRECT:

<? echo $foo; ?>
<?=$foo?>

CORRECT:

<?php echo $foo; ?>

One Statement Per Line

Never combine statements on one line.

INCORRECT:

$foo = 'this'; $bar = 'that'; $bat = str_replace($foo, $bar, $bag);

CORRECT:

$foo = 'this'; $bar = 'that';
$bat = str_replace($foo, $bar, $bag);

Strings

Always use single quoted strings unless you need variables parsed, and in cases where you do need variables parsed, use braces to prevent greedy token parsing. You may also use double-quoted strings if the string contains single quotes, so you do not have to use escape characters.

INCORRECT:

"My String"                 // no variable parsing, so no use for double quotes
"My string $foo"            // needs braces
'SELECT foo FROM bar WHERE baz = \'bag\''   // ugly

CORRECT:

'My String'
"My string {$foo}"
"SELECT foo FROM bar WHERE baz = 'bag'"

SQL Queries

MySQL keywords are always capitalized: SELECT, INSERT, UPDATE, WHERE, AS, JOIN, ON, IN, etc.

Break up long queries into multiple lines for legibility, preferably breaking for each clause:

INCORRECT:

// keywords are lowercase and query is too long for
// a single line (... indicates continuation of line)
$query = ee()->db->query("select foo, bar, baz, foofoo, foobar as raboof, foobaz from exp_pre_email_addresses where foo != 'oof' and baz != 'zab' order by foobaz limit 5, 100");

CORRECT:

$query = ee()->db->query("SELECT foo, bar, baz, foofoo, foobar AS raboof, foobaz
    FROM exp_pre_email_addresses
    WHERE foo != 'oof'
    AND baz != 'zab'
    ORDER BY foobaz
    LIMIT 5, 100");

MySQL Table Key Naming

Table key definitions must be explicitly named, to avoid accidental duplicate keys or inadvertent operations on the wrong index. Multiple column keys should be named distinctly, and preferably use all column names, separated with an underscore. (Additional info)

INCORRECT:

PRIMARY KEY (`field_name`)
PRIMARY KEY (`field_one`, `field_two`)

CORRECT:

PRIMARY KEY `field_name` (`field_name`)
PRIMARY KEY `field_one_field_two` (`field_one`, `field_two`)

Default Function Arguments

Whenever appropriate, provide function argument defaults, which helps prevent PHP errors with mistaken calls and provides common fallback values which can save a few lines of code. Example:

function foo($bar = '', $baz = FALSE)

Overlapping Tag Parameters

Avoid multiple tag parameters that have effect on the same thing. For instance, instead of include= and exclude=, perhaps allow include= to handle the parameter alone, with the addition of “not”, e.g. include="not bar". This will prevent problems of parameters overlapping or having to worry about which parameter has priority over another.

User Contributed Notes

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