public @Interface By

Annotates a parameter of a repository method, specifying a mapping to a persistent field:

• if a field name is specified, the parameter maps to the persistent field with the specified name, or
• if the special value id(this) is specified, the parameter maps to the unique identifier field or property.

Arguments to the annotated parameter are compared to values of the mapped persistent field.

The field name may be a compound name like address.city.

For example, for a Person entity with attributes ssn, firstName, lastName, and address we might have:

@Repository
public interface People {

    @Find
    Person findById(@By(ID) String id); // maps to Person.ssn

    @Find
    List<Person> findNamed(@By("firstName") String first,
                           @By("lastName") String last);

    @Find
    Person findByCity(@By("address.city") String city);
}

The By annotation is unnecessary when the method parameter name matches the entity attribute name and the application is compiled with the -parameters compiler option that makes parameter names available at runtime.

Thus, when this compiler option is enabled, the previous example may be written without the use of By:

@Repository
public interface People {

    @Find
    Person findById(String ssn);

    @Find
    List<Person> findNamed(String firstName,
                           String lastname);

    @Find
    Person findByCity(String address_city);
}