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我想执行一个简单的本机查询,但它不起作用:

@Autowired
private EntityManager em;

Query q = em.createNativeQuery("SELECT count(*) FROM mytable where username = :username");
em.setProperty("username", "test");
(int) q.getSingleResult();

为什么我得到这个例外？

org.hibernate.QueryException: Not all named parameters have been set: [username]