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1. JPQL查询

Employee employee = entityManager.createQuery(    "select e " +    "from Employee e " +    "left join fetch e.projects " +    "where " +    "    e.username = :username and " +    "    e.password = :password",    Employee.class).setParameter( "username", username).setParameter( "password", password).getSingleResult();

2. Criteria查询

CriteriaBuilder builder = entityManager.getCriteriaBuilder();CriteriaQuery
   
     query = builder.createQuery( Employee.class );Root
    
      root = query.from( Employee.class );root.
     fetch( "projects", JoinType.LEFT);query.select(root).where(    builder.and(        builder.equal(root.get("username"), username),        builder.equal(root.get("password"), password)    ));Employee employee = entityManager.createQuery( query ).getSingleResult();
    
   

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