@Override
public Category findById(Client client, Long id) {
    CriteriaBuilder builder = sessionFactory.getCurrentSession().getCriteriaBuilder();

    CriteriaQuery<Category> query = builder.createQuery(Category.class);

    Root<Category> root = query.from(Category.class);

    query.where(builder.equal(root.get("id"), id))
            .where(builder.and(builder.equal(root.get("client"), client)));

    query.select(root);

    return sessionFactory.getCurrentSession().createQuery(query).uniqueResultOptional().orElse(null);
}

select category0_.id as id1_0_0_, category0_.created as created2_0_0_, category0_.clientId as clientId4_0_0_, category0_.name as name3_0_0_, client1_.id as id1_1_1_, client1_.created as created2_1_1_, client1_.admin as admin3_1_1_, client1_.email as email4_1_1_, client1_.firstName as firstNam5_1_1_, client1_.lastName as lastName6_1_1_, client1_.password as password7_1_1_ from category category0_ inner join client client1_ on category0_.clientId=client1_.id where category0_.id=?

query.select(root).where(builder.and(builder.equal(root.get("id"), id), builder.equal(root.get("client"), client)));