RuleSupplier and ValidationSupplier

These interfaces let a ViewModel provide conditional UI rules and cross-field validations programmatically, as an alternative to using the @Rule annotation or bean validation constraints.

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RuleSupplier

Interface — io.mateu.uidl.interfaces.RuleSupplier

When a ViewModel implements RuleSupplier, Mateu merges the returned rules with any annotation-defined rules before sending them to the client. Rules are evaluated client-side: when the filter expression is truthy, the action is executed against the target field or action.

public interface RuleSupplier {
    List<Rule> rules();
}

Rule fields

Field	Type	Description
filter	String	Client-side JS expression; rule fires when this evaluates to truthy
action	RuleAction	What to do when the rule fires
fieldName	String	Target field name
fieldAttribute	RuleFieldAttribute	Which attribute of the field to modify
value	Object	Static value to set
expression	String	Client-side JS expression whose result is set as the value
actionId	String	Target action id (for RunAction)
result	RuleResult	Continue to keep evaluating rules, Stop to halt

RuleAction values

Value	Description
SetDataValue	Sets a field attribute (hidden, disabled, required, style, …)
SetStateValue	Sets a field value in the component state
SetAppStateValue	Sets a value in the application-level state
SetAppDataValue	Sets a data value at application level
RunAction	Triggers a named action
RunJS	Executes arbitrary JavaScript
SetAttributeValue	Sets an HTML attribute on the field element
SetCssClass	Adds or removes a CSS class
SetStyle	Sets an inline CSS style

RuleFieldAttribute values

required, disabled, hidden, pattern, minValue, maxValue, minLength, maxLength, css, style, theme, errorMessage, description

Example

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

    public String status;
    public double discount;

    @Override
    public List<Rule> rules() {
        return List.of(
            Rule.builder()
                .filter("state.status === 'closed'")
                .action(RuleAction.SetDataValue)
                .fieldName("discount")
                .fieldAttribute(RuleFieldAttribute.disabled)
                .expression("true")
                .result(RuleResult.Continue)
                .build(),
            Rule.builder()
                .filter("state.discount > 50")
                .action(RuleAction.SetDataValue)
                .fieldName("discount")
                .fieldAttribute(RuleFieldAttribute.errorMessage)
                .value("Discount cannot exceed 50%")
                .result(RuleResult.Continue)
                .build());
    }
}

Note: RuleSupplier is evaluated once on the server and the rules are sent to the client for repeated evaluation. For purely server-side visibility/disabled control, use VisibilitySupplier or DisabledSupplier instead — they remove or disable fields at render time without sending client expressions.

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ValidationSupplier

Interface — io.mateu.uidl.interfaces.ValidationSupplier

When a ViewModel implements ValidationSupplier, Mateu merges the returned validations with any bean-validation constraints before processing a form submission. Validations are evaluated server-side when an action is triggered.

public interface ValidationSupplier {
    List<Validation> validations();
}

Validation fields

Field	Type	Description
condition	String	Server-side SpEL expression; validation fails when this evaluates to true
fieldId	String	The field to highlight when the validation fails
message	String	Error message shown to the user

Example

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

    public LocalDate startDate;
    public LocalDate endDate;
    public double discount;

    @Override
    public List<Validation> validations() {
        return List.of(
            Validation.builder()
                .condition("endDate != null && startDate != null && endDate.isBefore(startDate)")
                .fieldId("endDate")
                .message("End date must be after start date")
                .build(),
            Validation.builder()
                .condition("discount < 0 || discount > 100")
                .fieldId("discount")
                .message("Discount must be between 0 and 100")
                .build());
    }
}