JPA EntityManager查询--使用原生sql查询

SQL查询多个字段

query.getResultList() 返回List类型，每个对象类型是Obejct类型的数组。List<Object[]>

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import java.math.BigDecimal; import java.util.List;   import javax.persistence.EntityManager; import javax.persistence.PersistenceContext; import javax.persistence.Query;   public class JpaDemoTest {     @PersistenceContext     private EntityManager em;       public void testJpaNativeQuery() {           BigDecimal classNo = null;              BigDecimal studentNo = null;         String remark = null;               String sql = "select t.class_no ,t.student_no ,t.remark   from t_student t where t.class_no =:class_no ";         Query query = em.createNativeQuery(sql);         query.setParameter("class_no", 20);         //返回Object[] 类型的List         List objecArraytList = query.getResultList();         for (int i = 0; i < objecArraytList.size(); i++) {             //每个结果是Obect[] 类型             Object[] obj = (Object[]) objecArraytList.get(i);             classNo = (BigDecimal) obj[0];             studentNo = (BigDecimal) obj[1];             remark = (String) obj[2];         }         System.out.println("classNo==" + classNo + ";studentNo==" + studentNo + ";remark==" + remark);     }   }

　　

SQL查询一个字段

query.getResultList() 返回List类型，每个对象类型是Obejct。List<Object>

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import java.math.BigDecimal; import java.util.List;   import javax.persistence.EntityManager; import javax.persistence.PersistenceContext; import javax.persistence.Query;   public class JpaDemoTest {     @PersistenceContext     private EntityManager em;       public void testJpaNativeQuery() {           BigDecimal classNo = null;                    String sql = "select t.class_no  from t_student t where t.class_no =:class_no ";         Query query = em.createNativeQuery(sql);         query.setParameter("class_no", 20);         //返回Object 类型的List         List objecArraytList = query.getResultList();         for (int i = 0; i < objecArraytList.size(); i++) {             //每个结果是Obect类型             classNo = (BigDecimal) objecArraytList.get(i);         }         System.out.println("classNo==" + classNo );     }   }