Data models in TYPO3
Data models in TYPO3 have to be maintained as two independent instruction sets. Any model needs one configuration file per database table called TCA in the TYPO3 lingo. These determine what properties (or rows) a given table has, what values are allowed, how they behave in the backend, and how they are stored in the database.
In addition, most custom extensions also implement an Extbase data model
on top of this table configuration, which enables the clean getting and
setting of values by means of one PHP object per database table. For each of
these, and in addition to the TCA, Extbase needs a model and a repository.
The model describes all properties, and a repository generates instances of
objects from the database. In addition to these, controllers orchestrate how
instances of objects may be accessed in the view. If the TCA configures tables
with multiple types (different sets of properties based on the value of
one property), these are implemented in models via inheritance: an
Abstract class defines all basic properties and other classes extend the
Abstract one to add the properties they need. While simple TCA tables and
models are mapped automatically, rules for model inheritance need to be made
explicit in the file Configuration/Extbase/Persistence/Classes.php.
Because the Extbase logic is built on top of a standard TCA, some aspects
may need to be implemented in both: default sorting of object instances,
for example, needs to be configured in both the TCA (for backend views) and
the repository (for accessing object instances in code and in the frontend),
multiple types in the same TCA table need to be adapted to class inheritance,
required fields must be marked both in the TCA and in the __construct()
method of a model, and if you want to limit the values that can be used in a
given property, this needs to be implemented in the TCA (for backend users)
and in the model's validators to allow for scenarios in which new object
instances are added through import routines, for example. While models use
camel case for properties (e.g., revisionDate), Extbase exptects their
respective database columns to use underscores (e.g., revision_date).
The 'view' in Extbase's model/view/controller logic is realised by TYPO3's templating engine called Fluid. In theory, Fluid also works with basic TCA configuration without the Extbase overhead, but a full object model maked Fluid more comfortable and allows you to add data programmatically instead of straight into the database.