hql ( hibernate query language ) 查询语言是面向对象的查询语言,也是在 hibernate 中最常见的。其语法和 sql 语法有一些相似,功能十分强大,几乎支持除特殊 sql 扩展外的所有查询功能。此种查询方式为 hibernate 官方推荐的标准查询方式。
以下我直接使用上一篇文章配置好的持久化类和工具类来写。
这篇文章我多以代码的形式来说明 hql 语法的使用。
// 基本语法 @test public void fun1() { session session = hibernateutils.opensession(); transaction tx = session.begintransaction(); // ----------------------------------------------------- string hql = "from customer"; query query = session.createquery(hql); list<customer> list = query.list(); system.out.println(list); // ----------------------------------------------------- tx.commit(); session.close(); }
// 条件查询 @test public void fun2() { session session = hibernateutils.opensession(); transaction tx = session.begintransaction(); // ----------------------------------------------------- string hql = "from customer where cust_id = ?"; string hql1 = "from customer where cust_id = :id";//另外一种查询语句写法 query query = session.createquery(hql1); // query.setparameter(0, 2l); query.setparameter("id", 2l); list<customer> list = query.list(); system.out.println(list); // ----------------------------------------------------- tx.commit(); session.close(); }
// 排序 @test public void fun3() { session session = hibernateutils.opensession(); transaction tx = session.begintransaction(); // ----------------------------------------------------- string hql = "from customer order by cust_id asc";// asc:升序 desc:降序 query query = session.createquery(hql); list<customer> list = query.list(); system.out.println(list); // ----------------------------------------------------- tx.commit(); session.close(); }
// 分页查询 @test public void fun4() { session session = hibernateutils.opensession(); transaction tx = session.begintransaction(); // ----------------------------------------------------- string hql = "from customer"; query query = session.createquery(hql); // 开始的下标=(当前页数-1)*每页条数 query.setfirstresult(0); query.setmaxresults(3); list<customer> list = query.list(); system.out.println(list); // ----------------------------------------------------- tx.commit(); session.close(); }
// 统计查询 // count // sum // avg // max // min @test public void fun5() { session session = hibernateutils.opensession(); transaction tx = session.begintransaction(); // ----------------------------------------------------- string hql1 = "select count(*) from customer"; // 统计条数 string hql2 = "select sum(cust_id) from customer"; // 求和 string hql3 = "select avg(cust_id) from customer"; // 求平均值 string hql4 = "select max(cust_id) from customer"; // 求最大值 string hql5 = "select min(cust_id) from customer"; // 求最小值 query query = session.createquery(hql3); number result = (number) query.uniqueresult(); system.out.println(result); // ----------------------------------------------------- tx.commit(); session.close(); }
// 投影查询 @test public void fun6() { session session = hibernateutils.opensession(); transaction tx = session.begintransaction(); // ----------------------------------------------------- string hql1 = "select new customer(cust_id,cust_name) from customer"; query query = session.createquery(hql1); list<customer> list = query.list(); system.out.println(list); // ----------------------------------------------------- tx.commit(); session.close(); }
以上查询都是单表查询,没有涉及多表查询,多表查询等我们熟悉好这几个查询,才继续学习多表查询。多表查询比单表查询复杂一点点。
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