Content classes for apps #

This page is for app developers who turn content classes into screens and data models. It explains how to learn what a class contains, how to use classIdentifier in the app, and how to stay robust when the site team changes a class.

Contents #

1. Learning the classes
2. classIdentifier as the switch
3. Surviving class changes
4. Fields that help apps

Learning the classes #

Three ways, from simplest to most complete:

expclass::identifiers gives a light map of class ids, identifiers and names to any signed-in user. The class services are declared in extension/expservices/classes/content/expclassservices.php.

classIdentifier as the switch #

Every node, object and list entry carries classIdentifier. Use it to choose the cell and the detail screen:

when (item.classIdentifier) {
    "article" -> ArticleCell
    "event"   -> EventCell
    "folder"  -> FolderCell (drill down with the list route)
    else      -> GenericCell (objectName only)
}

Always have the generic case: editors can place a class the app does not know in a folder it shows, and the app must not crash or hide the whole list because of it.

Surviving class changes #

Administrators can add, remove and reorder fields and change classes while the app is in users' hands. To stay robust:

• Read fields by identifier, never by position.
• Treat every field as optional, even if the class marks it required; old content may predate the requirement.
• Check type before parsing; skip a field whose type changed.
• Agree with the site team that renaming or removing a field the app uses is announced, like an API change.
• Add a test that reads one item of every class the app uses on a test installation and fails on unexpected types (A local test installation).

Fields that help apps #

If the site team builds or extends classes with the app in mind, a few fields make an app simpler:

How classes are designed is the site team's subject: Content classes for websites, Choosing datatypes.

Related pages #

• Fields and field values
• Designing your content model
• Content modeling for apps
• Free documentation: this page is free to copy, translate and improve under the GNU FDL 1.3.