cache_page (stores cache of anonymous pages)

cache_menu (stores cache for navigational menus)

cache_filter ( stores cache copy of node’s content)

• The drupal_page_cache_header() prepares the cache data by setting HTTP headers.
• Functions of cache API
  

Three important cache functions:

cache_set($cid, $table=’cache’, $data, $expire=CACHE_PERMANENT, $header=NULL)

where , $cid= Unique cache ID

$table= Name of the cache table to store the data, by default ‘cache’ table is used.

$data= data to store in the cache.

$expire=The cache data expire time. You can use CACHE_PERMANENT, CACHE_TEMPORARY or a Unix Timestamp. By default CACHE_PERMANENT is set.

$headers= The HTTP header passed to the browser.

cache_get($cid, $table=‘cache’ )

where $cid= The cahe id of the data to retrieve.

$table= The table name from which data retrieved. The cache table is used by Default.

cache_clear_all($cid=NULL,$table=NULL,$wildcard=NULL)

where $cid=if set,  clear only the given cache ID, otherwise delete all expire entries.

$table=the table to delete from.if not set entries from cache_block and cache_page table will be deleted.

$wildcard=if set to TRUE , all cache entries with ID contains a substring similar to $cid wil be deleted.

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Forms API

• The forms API abstracts forms into a nested array of properties and values.
• $form_values is array which holds form elements values.
• The form token (form unique id) is stored in the variables table as drupal_private_key.
• drupal_get_form() function interact with drupal form.
• hook_elements() function is used to define element type.
• hook_element() can be used to define your own element types in your module.
• element_info() hook collects all the properties for all form elements.

FORM PROPERTIES

• #validate property is used to validate the form elements.
• #base is used to apply same validator to several forms.
• #submit handles form submission. If there is no property named #submit, drupal looks for function name “formID_submit()” or failing that drupal again search for “#basevalue_submit”.
• #after_build property will call all functions of a form.
• #theme is used to set a theme to an existing form.
• #pre_render property used to call the functions just before the transformation of form from a data structure to HTML.
• #prepend, #suffix properties are used to prepend and append text to  the form elements. drupal also uses these properties while rendering the form.
• #method property is used to set the form method to post. By default it is set to post, Also get method is not supported by the form API.
• #tree : Setting #tree to TRUE gives a nested array of fields with there values. While #tree is set to FALSE, we get a flattened representation of field name and values.

FLOW of form formation:

when a module contains a form code is called by drupal the form datastructure renders form into html in the following sequence:

call drupal_get_form() -> call hook_elements()['defining element types such as radio buttons, chekcboxes, textfiels'] -> call elements_info() [information about the related properties ,values and functions] -> #validate property -> #submit property

Bibliography: Apress Pro Drupal Devlopement (ycu73k6ath)

How Sessions works on drupal:

The page request send by the browser includes a 32-character ID known as PHPSESSID under set- cookie tag, which is used as the key to the session information that drupal stores about session.

• The settings for session management are done in three files i.e. .htaccess, settings.php nad bootstarp.inc

• By default drupal uses the cookie based session management instead of URL base session management. If the browser doesn’t accept cookies , a session cannot be established

  • • The PHP directive ’sessions.use_only_cookies’ is set to 1 in settings.php to accept cookie based sessions.

    • The PHP directive ’sessions.use_trans_sid’ is set to 0 in settings.php to reject URL based sessions.

• At the installation time Drupal turns off the PHP’s ’session.auto_start’ functionality in .htaccess file to take full control over sessions.

Why Drupal need sessions?

• To handle the viewing preferences of the site content according to viewer status.

• To remember the viewing preferences: Drupal stores sessions in ’sessions’ table, the session table is used to associate the sessions Ids with the user ids to retrieve the viewing preferences of a user. It applies a join query on session and user tables using session ids and user ids to know the user role. Session data of a user is viewable by $user->session of $user object.

  • • To represent a session for anonymous user, the ’session’ table ‘uid’ column is set to 0.

    • To represent a session for login user, the ’session’ table ‘uid’ column is set to user Id with a new session Id such that the session does’nt get hijacked. If a user logs out, the row for that session is removed from the database immediately.

• To remember the comments preferences: In comment.module session is used to store viewing preferences for users, i.e.

  • • $_SESSIONS['comment_mode']=$mode

    • $_SESSIONS['comment_sort']=$order

    • $_SESSIONS['comment_comments_per_page']=$comments_per_page

• To handle file uploads

Session Life time

• Sessions lifetime related settings are located in settings.php, By default

  • • ini_set(’session.cache_expire’, 200000); // 138.9 days

    • ini_set(’session.cookie_lifetime’, 2000000); // 23.1 days

    • ini_set(’session.gc_maxlifetime’, 200000); // 55 hours

Other Information

• Writing session in the session table is the last task of drupal while serving pages.

• Drupal does not store session information , the first time a user visits a site. This is to reduce the load on the sessions table generated by crawlers.

• Drupal $user object is first built during the DRUPAL_BOOTSTRAP_SESSION phase of bootstrapping by sess_read().

• While deploying drupal on multiple subdomains, you can create a unique session name for each site by adding ini_set(’session.name’, ‘my-site-unique-name_PHPSESSID’); in settings.php

• If you need to store short term data for anonymous users, use the $_SESSION superglobal e.g.

  • • $_SESSION['anonymous_data']=$anonymous_data;

• If you want to store a permanent data to a user, save it in the $user object e.g.

  • • $user->login_name=$login_name; user_save();

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