如何在JPA中按名称获取Entity？

Question

I have entity

@Entity
@Table(name = "USER")
public class CrmUser implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String username;
    ...

And I have DAO with EntityManager How can I get user by username ?

@Override
    public User getUser(String login) throws Exception {
        User crmUser = (User) userJpaDao.getEntityManager()..............
        return crmUser;
    }

Answer 1

    @Entity
    @Table(name = "USER")
    @NamedQueries({
        @NamedQuery(
                name="CrmUser.getManagerByUserName",
                query="Select o From CrmUser o Where lower(o.username) = lower(:prm_sUserName)"
            )

    })
    public class CrmUser implements Serializable {

        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        private Long id;
        private String username;

Function To Retrieve User according to your username .

 private CrmUser findByUserName(String prm_userName){
    TypedQuery<CrmUser > v_objQuery;
    CrmUser obj_UserFoundWithUserName;
    EntityManager g_objUserEntityManager;
    g_objUserEntityManager= ?????.getEntityManager(); //provide your dao Class to get your entity Manager.
    v_objQuery = g_objUserEntityManager.createNamedQuery(CrmUser .class.getSimpleName() + ".getUserByUserName", CrmUser.class);
    v_objQuery.setParameter("prm_sUserName", prm_userName);
    obj_UserFoundWithUserName= v_objQuery.getSingleResult();
}