Hibernate JPA 元模型——引用嵌套属性？

Question

Suppose an entity model where an Employee has a Supervisor who has an id . Using hibernate-jpamodelgen to generate the meta model for the entities, how can I query a nested field?

For instance, "get all employees whose supervisor has id 4", using JpaSpecificationExecutor :

Page<Employee> getEmployeesBySupervisorId(int id) {
  return findAll((root, query, criteriaBuilder) -> {
    return criteriaBuilder.equal(root.get(Employee_.supervisor.id), id);
  });
}

Note that Employee_ is the model meta class for Employee (and was generated by Hibernate).

This code will produce an error because the id symbol cannot be found on type SingularAttribute<Employee, Supervisor> . I get that, but it seems like these should somehow be chainable. I can't find great examples of how to do this cleanly.

Answer 1

In order to navigate to related entities, you must use From#join() join method, which works well with MetaModel:

CriteriaQuery<Employee> cq = criteriaBuilder.createQuery(Employee.class);
Root<Employee> from = cq.from(Employee.class);
Predicate p = criteriaBuilder.equal(from.join(Employee_.supervisor).get(Supervisor_.id), id);

See also

Oracle's Java EE Tutorial - Using the Criteria API and Metamodel API to Create Basic Typesafe Queries