Database¶

Entities¶

Creating an object¶

To create an object in your code, you need to instantiate an ElggObject. Setting data is simply a matter of adding instance variables or properties. The built-in properties are:

``guid`` The entity’s GUID; set automatically
``owner_guid`` The owning user’s GUID
``site_guid`` The owning site’s GUID. This is set automatically when an instance of ElggObject gets created)
``subtype`` A single-word arbitrary string that defines what kind of object it is, for example blog
``access_id`` An integer representing the access level of the object
``title`` The title of the object
``description`` The description of the object

The object subtype is a special property. This is an arbitrary string that describes what the object is. For example, if you were writing a blog plugin, your subtype string might be blog. It’s a good idea to make this unique, so that other plugins don’t accidentally try and use the same subtype. For the purposes of this document, let’s assume we’re building a simple forum. Therefore, the subtype will be forum:

$object = new ElggObject();
$object->subtype = "forum";
$object->access_id = 2;
$object->save();

access_id is another important property. If you don’t set this, your object will be private, and only the creator user will be able to see it. Elgg defines constants for the special values of access_id:

ACCESS_PRIVATE Only the owner can see it
ACCESS_FRIENDS Only the owner and his/her friends can see it
ACCESS_LOGGED_IN Any logged in user can see it
ACCESS_PUBLIC Even visitors not logged in can see it

Saving the object will automatically populate the $object->guid property if successful. If you change any more base properties, you can call $object->save() again, and it will update the database for you.

You can set metadata on an object just like a standard property. Let’s say we want to set the SKU of a product:

$object->SKU = 62784;

If you assign an array, all the values will be set for that metadata. This is how, for example, you set tags.

Metadata cannot be persisted to the database until the entity has been saved, but for convenience, ElggEntity can cache it internally and save it when saving the entity.

Loading an object¶

By GUID¶

$entity = get_entity($guid);
if (!$entity) {
    // The entity does not exist or you're not allowed to access it.
}

But what if you don’t know the GUID? There are several options.

By user, subtype or site¶

If you know the user ID you want to get objects for, or the subtype, or the site, you have several options. The easiest is probably to call the procedural function elgg_get_entities:

$entities = elgg_get_entities(array(
    'type' => $entity_type,
    'subtype' => $subtype,
    'owner_guid' => $owner_guid,
));

This will return an array of ElggEntity objects that you can iterate through. elgg_get_entities paginates by default, with a limit of 10; and offset 0.

You can leave out owner_guid to get all objects and leave out subtype or type to get objects of all types/subtypes.

If you already have an ElggUser – e.g. elgg_get_logged_in_user_entity, which always has the current user’s object when you’re logged in – you can simply use:

$objects = $user->getObjects($subtype, $limit, $offset)

But what about getting objects with a particular piece of metadata?

By metadata¶

The function elgg_get_entities_from_metadata allows fetching entities with metadata in a variety of ways.

Displaying entities¶

In order for entities to be displayed in listing functions you need to provide a view for the entity in the views system.

To display an entity, create a view EntityType/subtype where EntityType is one of the following:

object: for entities derived from ElggObject user: for entities derived from ElggUser site: for entities derived from ElggSite group: for entities derived from ElggGroup

A default view for all entities has already been created, this is called EntityType/default.

Entity Icons¶

Entities all have a method called ->getIcon($size).

This method accepts a $size variable, which can be either ‘large’, ‘medium’, ‘small’ or ‘tiny’.

The method triggers a plugin hook - ‘entity:icon:url’. This is passed the following parameters:

‘entity’ : The entity in question ‘viewtype’ : The type of view e.g. ‘default’ or ‘mobile’. ‘size’ : The size.

The hook should return a url.

Hooks have already been defined, and will look in the following places for default values (in this order):

views/$viewtype/graphics/icons/$type/$subtype/$size.png
views/$viewtype/graphics/icons/$type/default/$size.png
views/$viewtype/graphics/icons/default/$size.png

Where

$viewtype : The type of view e.g. ‘default’ or ‘mobile’. $type : The type of entity - group, site, user, object. $subtype : Subtype of $type, e.g. blog, page. $size : Size - ‘large’, ‘medium’, ‘small’ or ‘tiny’

Adding, reading and deleting annotations¶

Annotations could be used, for example, to track ratings. To annotate an entity you can use the object’s annotate() method. For example, to give a blog post a rating of 5, you could use:

$blog_post->annotate('rating', 5);

To retrieve the ratings on the blog post, use $blogpost->getAnnotations('rating') and if you want to delete an annotation, you can operate on the ElggAnnotation class, eg $annotation->delete().

Retrieving a single annotation can be done with get_annotation() if you have the annotation’s ID. If you delete an ElggEntity of any kind, all its metadata, annotations, and relationships will be automatically deleted as well.

Extending ElggEntity¶

If you derive from one of the Elgg core classes, you’ll need to tell Elgg how to properly instantiate the new type of object so that get_entity() et al. will return the appropriate PHP class. For example, if I customize ElggGroup in a class called “Committee”, I need to make Elgg aware of the new mapping. Following is an example class extension:

// Class source
class Committee extends ElggGroup {

    protected function initializeAttributes() {
        parent::initializeAttributes();
        $this->attributes['subtype'] = 'committee';
    }

    // more customizations here
}

function committee_init() {

    register_entity_type('group', 'committee');

    // Tell Elgg that group subtype "committee" should be loaded using the Committee class
    // If you ever change the name of the class, use update_subtype() to change it
    add_subtype('group', 'committee', 'Committee');
}

register_elgg_event_handler('init', 'system', 'committee_init');

Now if you invoke get_entity() with the GUID of a committee object, you’ll get back an object of type Committee.

This template was extracted from the definition of ElggFile.

Advanced features¶

Entity Icons¶

A url for an icon representing a given entity can be retrieved by the getIcon() method.

This is handy as it provides a generic interface which allows the Elgg framework to draw an icon for your data - it also allows you to override icons for existing data types - for example providing Gravatar support for user icons.

If no icon can be provided for the data type a default one is used, defined either by your current theme or the Elgg default.

Overriding the url for a specific instance¶

To override the icon of a specific instance of an entity in a non-permanent and one off way, you can use the entity’s setIcon() method.

Replacing icons via the views interface¶

If you want to provide an icon for a new data type, or override an existing one you can do this simply through the views interface.

Views are in the format:

icon/``[TYPE]``/``[SUBTYPE]``/``[SIZE]``

Where:

[TYPE]: is the elgg type of the object - “user”, “group”, “object” or “site”. [SUBTYPE]: is the specific subtype of the object, or “default” for the default icon for the given type. [SIZE]: the size, one of the following “master”, “large”, “medium”, “small”, “topbar” or “tiny”.

This view should contain the URL to the image only.

Overriding icons via a handler¶

The final way to replace icons is via a handler to a plugin hook.

This method lets you perform some additional logic in order to decide better which url to return.

The hook triggered is:

trigger_plugin_hook('entity:icon:url', $entity->getType(), array('entity' => $entity, 'viewtype' => $viewtype, 'size' => $size));

`` ``

Entity URLs¶

Entity urls are provided by the getURL() interface and provide the Elgg framework with a common way of directing users to the appropriate display handler for any given object.

For example, a profile page in the case of users.

The url is set using the elgg\_register\_entity\_url\_handler() function. The function you register must return the appropriate url for the given type - this itself can be an address set up by a page handler.

The default handler is to use the default export interface.

Pre-1.8 Notes¶

update_subtype(): This function is new in 1.8. In prior versions, you would need to edit the database by hand if you updated the class name associated with a given subtype.

elgg_register_entity_url_handler(): This function is new in 1.8. It deprecates register_entity_url_handler(), which you should use if developing for a pre-1.8 version of Elgg.

elgg_get_entities_from_metadata(): This function is new in 1.8. It deprecates get_entities_from_metadata(), which you should use if developing for a pre-1.8 version of Elgg.