Hydratable

Interface — io.mateu.uidl.interfaces.Hydratable

By default, Mateu hydrates a ViewModel by iterating over the component state sent by the browser and writing each key-value pair into the matching field via reflection. When a ViewModel implements Hydratable, this automatic injection is skipped entirely and hydrate() is called instead, letting the ViewModel deserialise the request state however it needs.

public interface Hydratable {
    void hydrate(HttpRequest httpRequest);
}

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When to use it

Use Hydratable when:

• The ViewModel’s internal structure does not map 1-to-1 with the state fields the client sends.
• You need to deserialise state into a complex or nested structure that reflection cannot handle.
• You want to apply validation or transformation during hydration itself.
• The ViewModel wraps a domain object that should not expose public setters.

For the common case of running extra logic after automatic hydration, use PostHydrationHandler instead — it is simpler and does not require you to manually read all fields from the request.

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Execution order

1. ViewModel instantiated
2. hydrate() called ← replaces automatic field injection
3. PostHydrationHandler.onHydrated() called (if also implemented)
4. Action executed (if the request is an action call)
5. UI rendered and sent to the client

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Example

@UI("/orders/{id}")
public class OrderForm implements Hydratable {

    private Order order;  // domain object — no public setters

    @Override
    public void hydrate(HttpRequest httpRequest) {
        var state = httpRequest.getState(Map.class);
        var id = (String) state.get("id");
        this.order = orderRepository.findById(id).orElseThrow();
        // apply any edits the user made
        if (state.containsKey("status")) {
            this.order.setStatus((String) state.get("status"));
        }
    }

    public String getId()     { return order.getId(); }
    public String getStatus() { return order.getStatus(); }
}

Note: When implementing Hydratable, you are responsible for reading all relevant fields from httpRequest. Any state the client sends that you do not read in hydrate() will not be applied to the ViewModel.