A IModel wraps the actual model Object used by a Component. IModel implementations are used as a facade for the real model so that users have control over the actual persistence strategy. Note that objects implementing this interface will be stored in the Session. Hence, you should use (non-transient) instance variables sparingly.

• Basic Models - To implement a basic (non-detachable) model which holds its entire state in the Session, you can either subclass AbstractModel , or use the simple model wrapper Model directly.
• Detachable Models - IModel inherits a hook, detach() , so that interface implementers can detach transient information when a model is no longer being actively used by the framework. This reduces memory use and reduces the expense of replicating the model in a clustered server environment. To implement a detachable model, you should generally extend AbstractDetachableModel instead of implementing IModel directly.
• Nested Models - IModels can be nested and the innermost model is also known as the "root" model since it is the model on which the outer models rely. The getNestedModel() method on IModel gets any nested model within the given model. This allows Component.sameRootModel() to compare two models to see if they both have the same root model (the same most nested model).

  For example, a Form might have a Person model and then a TextField might have a PropertyModel which is the "name" property of the Person model. In this case, PropertyModel will implement getNestedModel(), returning the Person model which is the root model of the property model.

• Property Models - The AbstractPropertyModel class provides default functionality for property models. A property model provides access to a particular property of its wrapped model.
• Compound Property Models - The IModel interface is parameterized by Component, allowing a model to be shared among several Components. When the getObject(Component) method is called, the value returned will depend on the Component which is asking for the value. Likewise, the setObject(Component, Object) method sets a different property depending on which Component is doing the setting. For more information on CompoundPropertyModels and model inheritance, see CompoundPropertyModel and Page .