How to Validate the Combination of Multiple Fields in JPA 2.0/Hibernate?

Question

How can I validate the combination of two fields in a JPA 2.0 model?

public class MyModel {
    private Integer value1;
    private String value2;

    public Integer getValue1() {
        return value1;
    }

    public String getValue2() {
        return value2;
    }
}

Answer

In JPA 2.0/Hibernate, conditional validation on field combinations can be achieved by implementing custom validation. This allows you to define complex validation logic beyond the standard annotations.

import javax.validation.Constraint;
import javax.validation.ConstraintValidator;
import javax.validation.ConstraintValidatorContext;
import javax.validation.Payload;

@Constraint(validatedBy = MyModelValidator.class)
@Target({ ElementType.TYPE })
@Retention(RetentionPolicy.RUNTIME)
public @interface ValidMyModel {
    String message() default "Either value1 or value2 must be non-null.";
    Class<?>[] groups() default {};
    Class<? extends Payload>[] payload() default {};
}

public class MyModel {
    private Integer value1;
    private String value2;

    @ValidMyModel
    public Integer getValue1() {
        return value1;
    }

    public String getValue2() {
        return value2;
    }
}

public class MyModelValidator implements ConstraintValidator<ValidMyModel, MyModel> {
    @Override
    public boolean isValid(MyModel model, ConstraintValidatorContext context) {
        return (model.getValue1() != null || model.getValue2() != null);
    }
}

Causes

If both fields are null, the model should be considered invalid, but using standard @NotNull annotations makes both fields checked independently.

Solutions

Create a custom validation annotation that checks the logic for both fields together.
Implement a validator class that contains the validation logic for the combination of the fields.

Common Mistakes

Mistake: Not implementing the 'isValid' method correctly in the custom validator.

Solution: Ensure that the logic checks for the combination of fields correctly. Only one of the fields should not be null for the validation to pass.

Mistake: Forgetting to annotate the class with custom validation.

Solution: Make sure the model class is annotated with the newly created @ValidMyModel annotation.

Helpers

JPA validation
Hibernate validation
custom validation annotation
field combination validation in Hibernate
JPA model validation