Programming Social Applications

Link

The Link element allows a developer to take advantage of application life-cycle events defined by a container. Such events might be application installs or uninstalls, or any other event in the day-to-day life of a social application. The container supports these features by sending relevant query parameters denoting the event to a URL endpoint specified within the Link node.

A Link node may take the following form under the ModulePrefs element:

<ModulePrefs>
    <Link rel="event" href="http://www.mysite.com/ping.php" method="POST" />
    <Link rel="event.addapp" href="http://www.mysite.com/add_app.php" />
    <Link rel="event.removeapp" href="http://www.mysite.com/remove_app.php" />
</ModulePrefs>

As you can see in the preceding example, the Link node has several associated attributes. They are listed in Table 3-5.

Table 3-5. Link attributes

Attribute	Description
rel	The string value that denotes the event being triggered. This value is required.
href	The URL to make a request to once the event has been triggered. This value is required.
method	The HTTP request method, either GET or POST, to use when making a request to the URL supplied in the href attribute. The default request method is GET. This is an optional attribute.

If a Link node is specified with a rel of opensocialevent (e.g., rel="event"), then any undefined life-cycle event types will be sent through to that href value by default. If there are one or more Link nodes with a rel of opensocialevent.type (e.g., rel="event.addapp"), then any ...