Chapter 11: Truth of Models - The soul of Wicket

IModel

IModel<T> abstracts data access for components. It decouples UI elements from storage and retrieval details.

PropertyModel

PropertyModel binds to bean properties and simplifies common form/page bindings.

CompoundPropertyModel

CompoundPropertyModel reduces boilerplate by resolving child component IDs against a shared backing object.

LoadableDetachableModel

Use LoadableDetachableModel when data should be reloaded lazily per request and detached safely to reduce session footprint.

Practical Pitfalls

Problem
Model bindings become hard to follow and maintenance gets risky.

Cause
Too much reliance on implicit compound bindings hides intent and ownership.

Solution
Make critical bindings explicit with focused models so intent remains readable.
Problem
Property evaluation behaves differently by lifecycle timing.

Cause
Resolution happens before component hierarchy/context is fully established.

Solution
Resolve model expressions after hierarchy setup phases.
Problem
Session memory grows over time.

Cause
Detachable model assumptions are broken and heavy references remain alive.

Solution
Design for load-on-demand and detach-at-end-of-request discipline.
Problem
Final values differ depending on edit sequence.

Cause
Multiple form components mutate one shared model without explicit ordering.

Solution
Separate models by responsibility, or define deterministic update order with tests.