Cross-field validation

Some validation rules depend on the values of multiple fields. Teki supports two mechanisms for this: conditional blocks with when() and whole-object invariants with constraint().

Both are available on schemas built with Teki.fromRules(...). They cannot be added to cached schemas obtained from Teki.from(Class).

Conditional validation

when(predicate, ...builders) runs a set of validation rules only when a predicate on the full object holds. The predicate receives the object being validated.

Teki schema = Teki.fromRules(
    number("age").required(),
    string("parentName").optional(),
    string("guardianEmail").optional()
)
.when(
    p -> p.getAge() < 18,
    string("parentName").required(),
    string("guardianEmail").required().email()
);

When age < 18, both parentName and guardianEmail are required and validated against their rules. When the predicate does not hold, those builders are skipped entirely.

Multiple when() blocks can be chained. Each is evaluated independently.

Teki schema = Teki.fromRules(
    string("accountType").required(),
    string("vatNumber").optional(),
    string("companyName").optional()
)
.when(
    p -> "business".equals(p.getAccountType()),
    string("vatNumber").required().pattern("[A-Z]{2}[0-9]+"),
    string("companyName").required().min(2)
);

You can also pass pre-built Validatable instances instead of builders:

Validatable vatRule = string("vatNumber").required().build();
schema.when(p -> "business".equals(p.getAccountType()), vatRule);

Whole-object invariants

constraint(predicate, field, message) checks an invariant after all per-field validation completes. The predicate should return true when the invariant holds. When it returns false, an error is attached to the named field.

Teki schema = Teki.fromRules(
    string("password").required(),
    string("passwordConfirm").required()
)
.constraint(
    p -> p.getPassword().equals(p.getPasswordConfirm()),
    "passwordConfirm",
    "Passwords do not match"
);

Use constraint() for checks that span fields but do not require running additional rule chains. Use when() when the condition should activate one or more full field validations.