HQL的内连接查询
对于HQL内链接查询,查询的是两张表的数据,这两张表的数据首先是保存在数组之中,然后在将每一个数组保存在List集合之中进行返回
代码片段:
1 @Test 2 // 内连接 3 public void fun1() { 4 SessionFactory factory = null; 5 Session session = null; 6 Transaction tx = null; 7 try { 8 factory = Tools.getSessionFactory(); 9 session = factory.openSession(); 10 tx = session.beginTransaction(); 11 // mans是Customer实体类的关联LinkMan实体类的一个集合属性 12 Query query = session.createQuery("from Customer c inner join c.mans"); 13 List list = query.list(); 14 tx.commit(); 15 } catch (Exception e) { 16 tx.rollback(); 17 e.printStackTrace(); 18 } finally { 19 session.close(); 20 } 21 }
debug截图:
HQL迫切内连接查询
hql的迫切内连接查询,只需要将内连接查询加上一个fetch就行,如下:
1 from Customer c inner join fetch c.mans
迫切内连接和内连接的主要的区别是,内连接的List每部分是一个对象数组,而迫切内连接的List每部分返回的是一个对象。
代码片段:
1 @Test 2 // 迫切内连接 3 public void fun2() { 4 SessionFactory factory = null; 5 Session session = null; 6 Transaction tx = null; 7 try { 8 factory = Tools.getSessionFactory(); 9 session = factory.openSession(); 10 tx = session.beginTransaction(); 11 // mans是Customer实体类的关联LinkMan实体类的一个集合属性 12 Query query = session.createQuery("from Customer c inner join fetch c.mans"); 13 List list = query.list(); 14 tx.commit(); 15 } catch (Exception e) { 16 tx.rollback(); 17 e.printStackTrace(); 18 } finally { 19 session.close(); 20 } 21 }
Debug截图:
HQL的左外连接
左外连接的hql语句:
1 from Customer c left outer join 关联另一个实体的属性
代码片段:
1 @Test 2 // 左外连接 3 public void fun3() { 4 SessionFactory factory = null; 5 Session session = null; 6 Transaction tx = null; 7 try { 8 factory = Tools.getSessionFactory(); 9 session = factory.openSession(); 10 tx = session.beginTransaction(); 11 Query query = session.createQuery("from Customer c left outer join c.mans"); 12 List list = query.list(); 13 tx.commit(); 14 } catch (Exception e) { 15 tx.rollback(); 16 e.printStackTrace(); 17 } finally { 18 session.close(); 19 } 20 }
Debug截图:
HQL的左外迫切连接
迫切左外连接hql语句:
from Customer c left outer join fetch 关联的另一个实体类在此类中的属性
代码片段:
1 @Test 2 // 迫切左外连接 3 public void fun4() { 4 SessionFactory factory = null; 5 Session session = null; 6 Transaction tx = null; 7 try { 8 factory = Tools.getSessionFactory(); 9 session = factory.openSession(); 10 tx = session.beginTransaction(); 11 Query query = session.createQuery("from Customer c left outer join fetch c.mans"); 12 List list = query.list(); 13 tx.commit(); 14 } catch (Exception e) { 15 tx.rollback(); 16 e.printStackTrace(); 17 } finally { 18 session.close(); 19 } 20 }
Debug截图:
时间: 2024-10-17 05:12:20