new-rule

name	new-rule
description	Guide for creating a Rule in rulii — lambda-based and class-based styles, conditions, actions, otherwise, preCondition, and running rules manually
user-invocable	true

Creating a Rule in rulii

Use this guide when the user asks to create, compose, or explain a Rule.

A Rule is an if / then / otherwise construct: a Condition that is tested, one or more Actions run when it passes, and an optional otherwise Action run when it fails.

---

1. Minimal Rule (lambda-based)

Rule rule = Rule.builder()
        .name("AgeCheck")
        .given(condition((Integer age) -> age >= 18))
        .build();

• Rule.builder() returns the singleton RuleBuilder.
• .name(String) is required for lambda-based rules.
• .given(Condition) sets the main condition. A rule with no condition defaults to always-true (with a warning).

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2. Full builder API

Rule.builder()
  .name("RuleName")             // required for lambda rules; must match [A-Za-z][A-Za-z0-9_]*
  .name("RuleName", "desc")     // name + description shorthand
  .description("...")           // optional description
  .preCondition(condition)      // skip this rule entirely if false (no then/otherwise called)
  .given(condition)             // main condition — required
  .then(action)                 // action(s) when condition is true (chainable)
  .then(action2)
  .otherwise(action)            // action when condition is false
  .build()

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3. Condition and Action factories

Import the static helpers for concise lambda syntax:

import static org.rulii.model.condition.Conditions.condition;
import static org.rulii.model.action.Actions.action;

Condition examples:

// Single binding resolved by parameter name
condition((Integer age) -> age >= 18)

// Multiple bindings
condition((String firstName, String lastName) -> firstName != null && lastName != null)

// Always true / false
Conditions.TRUE()
Conditions.FALSE()

// Combine with .and() / .or() / .negate()
condition((Integer age) -> age >= 18).and(condition((String email) -> email.contains("@")))

Action examples:

// Mutation via Binding<T>
action((Binding<Integer> count) -> count.setValue(count.getValue() + 1))

// Side effect with a plain value
action((String name) -> System.out.println("Hello " + name))

// Access the full Bindings
action((Bindings bindings) -> bindings.bind(result -> "done"))

// No-op
Actions.EMPTY_ACTION()

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4. PreCondition vs. main Condition

	PreCondition	Condition
Fails → result	SKIP (no then/otherwise)	otherwise action runs (if set)
Typical use	Guard — wrong type, missing context	Business logic
Class-based	@PreCondition annotation	@Given annotation

Rule rule = Rule.builder()
        .name("NumericCheck")
        .preCondition(condition((Object value) -> value instanceof String))  // SKIP if not a String
        .given(condition((String value) -> value.matches("\\d+")))
        .otherwise(action((RuleViolations rv) -> rv.add(...)))
        .build();

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5. Class-based Rules

Annotate a plain class — rulii discovers @Given, @Then, @Otherwise, @PreCondition by annotation:

@org.rulii.annotation.Rule
@Description("User must be of legal age")
public class AgeCheckRule {

    @PreCondition
    public boolean isApplicable(Object value) {
        return value instanceof Integer;
    }

    @Given
    public boolean isValid(Integer age) {
        return age >= 18;
    }

    @Then
    public void onPass(Bindings bindings) {
        // runs when condition is true
    }

    @Otherwise
    public void onFail(RuleViolations violations) {
        // runs when condition is false
    }
}

// Build from class
Rule rule = Rule.builder().build(AgeCheckRule.class);

// Build from instance (useful when constructor arguments are needed)
Rule rule = Rule.builder().build(new AgeCheckRule());

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6. Class-based Rules with Spring injection

In a Spring context, rules discovered via @RuleScan are Spring-managed. Use @Value, @Autowired, or constructor injection:

@Rule
@Description("Validates that fromDate is before toDate.")
public class ConsistentDateRule {

    @Value("${errorCode.100}")
    private String message;

    @PreCondition
    public boolean check(LocalDate fromDate, LocalDate toDate) {
        return fromDate != null && toDate != null;
    }

    @Given
    public boolean isValid(LocalDate fromDate, LocalDate toDate) {
        return fromDate.isBefore(toDate);
    }

    @Otherwise
    public void otherwise(LocalDate fromDate, LocalDate toDate, RuleViolations violations) {
        violations.add(RuleViolation.builder().build("consistentDateRule", "errorCode.100", message));
    }
}

For rules built manually outside the scan, pass ObjectFactory to retain Spring support:

@Bean
public Rule myRule(ObjectFactory objectFactory) {
    return Rule.builder()
            .with(MyRule.class, objectFactory)
            .build();
}

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7. Running a Rule

Via RuleContext (normal path — used in RuleSets):

Bindings bindings = Bindings.builder().standard();
bindings.bind(age -> 25);
RuleContext ctx = RuleContext.builder().build(bindings);

RuleResult result = rule.run(ctx);
// result.getStatus() → PASS, FAIL, or SKIP

Manually testing the condition (no actions fired):

// Pass BindingDeclaration lambdas — parameter name becomes binding name
boolean passes = rule.getCondition().isTrue(age -> 25);
boolean passes = rule.getCondition().isTrue(age -> 25, email -> "[e-mail]");

// Or with a RuleContext
boolean passes = rule.isTrue(ctx);

Shorthand run with inline bindings:

rule.run(age -> 25, name -> "Alice");

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8. RuleResult status values

Status	Meaning
PASS	preCondition passed, condition returned true, then-actions ran
FAIL	preCondition passed, condition returned false, otherwise ran
SKIP	preCondition returned false — rule was bypassed entirely

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Common Mistakes

Mistake	Fix
No .name() on a lambda rule	Required — the framework throws IllegalArgumentException
Calling .run(bindings) instead of .run(ctx)	Wrap bindings: RuleContext.builder().build(bindings), then rule.run(ctx)
Expecting otherwise to fire on SKIP	It doesn't — only fires when condition is false, not when preCondition is false
Passing a Bindings container as a single lambda to isTrue()	Pass individual BindingDeclaration lambdas: isTrue(age -> 25, name -> "x")
Spring @Value not injected in manually-built rule	Use Rule.builder().with(MyRule.class, objectFactory).build() instead of Rule.builder().build(MyRule.class)