mybatis之旅第六篇-关联查询
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一、引言
通过动态SQL我们可以进行复杂SQL的编写,但之前的例子都是单表查询,在实际开发中,当然不可能都是单表,很多时候我们需要进行关联多表查询(有些公司为了性能还是尽量的使用单表查询),表与表之间的关系分为一对一,一对多,多对多,我们讲讲这三种是如何编写的。
先进行表和实体的创建:
CREATE TABLE `user` ( `id` int(11) NOT NULL AUTO_INCREMENT, `username` varchar(32) NOT NULL COMMENT \'用户名称\', `birthday` date DEFAULT NULL COMMENT \'生日\', `sex` char(1) DEFAULT NULL COMMENT \'性别\', `address` varchar(256) DEFAULT NULL COMMENT \'地址\', PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=27 DEFAULT CHARSET=utf8; -- ---------------------------- -- Records of user -- ---------------------------- INSERT INTO `user` VALUES (\'1\', \'王五\', null, \'2\', null); INSERT INTO `user` VALUES (\'10\', \'张三\', \'2014-07-10\', \'1\', \'北京市\'); INSERT INTO `user` VALUES (\'16\', \'张小明\', null, \'1\', \'河南郑州\'); INSERT INTO `user` VALUES (\'22\', \'陈小明\', null, \'1\', \'河南郑州\'); INSERT INTO `user` VALUES (\'24\', \'张三丰\', null, \'1\', \'河南郑州\'); INSERT INTO `user` VALUES (\'25\', \'陈小明\', null, \'1\', \'河南郑州\'); INSERT INTO `user` VALUES (\'26\', \'王五\', null, null, null); DROP TABLE IF EXISTS `order`; CREATE TABLE `order` ( `id` int(11) NOT NULL AUTO_INCREMENT, `user_id` int(11) NOT NULL COMMENT \'下单用户id\', `number` varchar(32) NOT NULL COMMENT \'订单号\', `createtime` datetime NOT NULL COMMENT \'创建订单时间\', `note` varchar(100) DEFAULT NULL COMMENT \'备注\', PRIMARY KEY (`id`), KEY `FK_order_1` (`user_id`), CONSTRAINT `FK_order_id` FOREIGN KEY (`user_id`) REFERENCES `user` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION ) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8; -- ---------------------------- -- Records of order -- ---------------------------- INSERT INTO `order` VALUES (\'3\', \'1\', \'1000010\', \'2015-02-04 13:22:35\', null); INSERT INTO `order` VALUES (\'4\', \'1\', \'1000011\', \'2015-02-03 13:22:41\', null); INSERT INTO `order` VALUES (\'5\', \'10\', \'1000012\', \'2015-02-12 16:13:23\', null);
User:
@Data public class User implements Serializable { private Integer id; // 用户姓名 private String username; // 性别 private String sex; // 生日 private Date birthday; // 地址 private String address; }
Order:
@Data public class Order { // 订单id private int id; // 用户id private Integer userId; // 订单号 private String number; // 订单创建时间 private Date createtime; // 备注 private String note; }
二、
订单表与用户表,一个订单是由一个客户创建的,当我们通过订单去反查用户时,就是一对一关系。
有两种方式可以实现
2.1、
@Data public class OrderUserVO extends Order { /** * 客户名称 */ private String username; /** * 客户地址 */ private String address; }
xml文件:
<select id="queryOrderUser" resultType="com.yuanqinnan.pojo.OrderUserVO"> SELECTo.id,o.user_id,userId,o.number,o.createtime,o.note,u.username,u.address FROM `order` o LEFT JOIN `user` u ON o.user_id = u.id </select>
接口:
public interface OrderMapper { List<Order> queryOrderAll(); List<Order> queryOrderAll2(); List<OrderUserVO> queryOrderUser(); }
测试:
@Test public void queryOrderUser(){ SqlSession sqlSession = this.sqlSessionFactory.openSession(); OrderMapper orderMapper = sqlSession.getMapper(OrderMapper.class); List<OrderUserVO> list = orderMapper.queryOrderUser(); for (OrderUserVO u : list) { System.out.println(u); } sqlSession.close(); }
结果:
定义专门的pojo类作为输出类型,其中定义了sql查询结果集所有的字段。此方法较为简单,企业中使用普遍。
2.2、
@Data public class Order { // 订单id private int id; // 用户id private Integer userId; // 订单号 private String number; // 订单创建时间 private Date createtime; // 备注 private String note; /** * 客户 */ private User user; }
先定义resultMap:
<resultMap type="com.yuanqinnan.model.Order" id="orderUserResultMap"> <id property="id" column="id"/> <result property="userId" column="user_id"/> <result property="number" column="number"/> <result property="createtime" column="createtime"/> <result property="note" column="note"/> <!-- association :配置一对一属性 --> <!-- property:order里面的User属性名 --> <!-- javaType:属性类型 --> <association property="user" javaType="user"> <!-- id:声明主键,表示user_id是关联查询对象的唯一标识--> <id property="id" column="user_id"/> <result property="username" column="username"/> <result property="address" column="address"/> </association> </resultMap>
再添加查询
<!-- 一对一关联,查询订单,订单内部包含用户属性 --> <select id="queryOrderUserResultMap" resultMap="orderUserResultMap"> SELECT o.id,o.user_id,o.number,o.createtime,o.note,u.username,u.address FROM `order` o LEFT JOIN `user` u ON o.user_id = u.id </select>
接口:
List<Order> queryOrderUserResultMap();
测试:
@Test public void queryOrderUserResultMap(){ SqlSession sqlSession = this.sqlSessionFactory.openSession(); OrderMapper orderMapper = sqlSession.getMapper(OrderMapper.class); List<Order> list = orderMapper.queryOrderUserResultMap(); for (Order u : list) { System.out.println(u); } sqlSession.close(); }
结果:
三、
一个客户会创建多个订单,当我们查询客户订单时,就会产生一对多的情况,我们以此为例。
首先,我们在User类中增加订单列表
@Data public class User implements Serializable { //id private Integer id; //用户姓名 private String username; //性别 private String sex; //生日 private Date birthday; //地址 private String address; //订单列表 private List<Order> orderList; }
然后增加resultMap:
<resultMap type="com.yuanqinnan.model.Order" id="orderUserResultMap"> <id property="id" column="id"/> <result property="userId" column="user_id"/> <result property="number" column="number"/> <result property="createtime" column="createtime"/> <result property="note" column="note"/> <!-- association :配置一对一属性 --> <!-- property:order里面的User属性名 --> <!-- javaType:属性类型 --> <association property="user" javaType="user"> <!-- id:声明主键,表示user_id是关联查询对象的唯一标识--> <id property="id" column="user_id"/> <result property="username" column="username"/> <result property="address" column="address"/> </association> </resultMap>
增加查询:
<!-- 一对一关联,查询订单,订单内部包含用户属性 --> <select id="queryOrderUserResultMap" resultMap="orderUserResultMap"> SELECT o.id,o.user_id,o.number,o.createtime,o.note,u.username,u.address FROM `order` o LEFT JOIN `user` u ON o.user_id = u.id </select>
测试:
@Test public void queryUserOrder(){ SqlSession sqlSession = this.sqlSessionFactory.openSession(); UserMapper userMapper = sqlSession.getMapper(UserMapper.class); List<User> list = userMapper.queryUserOrder(); for (User u : list) { System.out.println(u); } sqlSession.close(); }
结果:
四、
CREATE TABLE `product` ( `id` int(11) NOT NULL AUTO_INCREMENT, `name` varchar(50) DEFAULT NULL COMMENT \'产品名称\', PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf; -- ---------------------------- -- Records of product -- --------------------------- INSERT INTO product VALUES(\'1\',\'笔记本电脑\'); INSERT INTO product VALUES(\'2\',\'小米手机\'); CREATE TABLE `order_product` ( `id` int(11) NOT NULL AUTO_INCREMENT, `oid` int(11) DEFAULT NULL COMMENT \'订单id\', `pid` int(11) DEFAULT NULL COMMENT \'产品id\', PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8 -- ---------------------------- -- Records of order_product -- --------------------------- INSERT INTO order_product VALUES(\'1\',\'3\',\'1\'); INSERT INTO order_product VALUES(\'2\',\'3\',\'2\'); INSERT INTO order_product VALUES(\'3\',\'4\',\'1\');
我们可能遇到的多对多查询是:查询这个订单的所有产品或者查询这个产品的所有订单
那这个时候我们的订单和产品表里都应该对应多个中间表,实体就应该这么设计:
order实体增加中间表:
@Data public class Order { // 订单id private int id; // 用户id private Integer userId; // 订单号 private String number; // 订单创建时间 private Date createtime; // 备注 private String note; //客户 private User user; //中间表 private List<OrderProduct> products; }
OrderProduct:
@Data public class OrderProduct { private Integer id; //订单主键 private Integer oid; //产品主键 private Integer pid; //订单 private Order order; //产品 private Product product; }
product:
@Data public class Product { //产品id private Integer id; //产品名称 private String name; //中间表 List<OrderProduct> orders; }
resultmap:
<resultMap type="com.yuanqinnan.model.Order" id="orderBean"> <id column="id" property="id"/> <result property="userId" column="user_id"/> <result property="number" column="number"/> <result property="createtime" column="createtime"/> <result property="note" column="note"/> <collection property="products" ofType="com.yuanqinnan.model.OrderProduct"> <id column="oiid" property="id"/> <result column="oid" property="oid"/> <result column="pid" property="pid"/> <association property="product" javaType="com.yuanqinnan.model.Product"> <id column="pid" property="id"/> <result column="pname" property="name"/> </association> </collection> </resultMap>
新增查询订单的产品信息方法:
<select id="listOrder" resultMap="orderBean"> SELECT o.*, o.id oid, p.id pid, oi.id oiid, p.NAME pname FROM `order` o LEFT JOIN order_product oi ON o.id = oi.oid LEFT JOIN product p ON p.id = oi.pid </select>
测试:
@Test public void listOrder(){ SqlSession sqlSession = this.sqlSessionFactory.openSession(); OrderMapper orderMapper = sqlSession.getMapper(OrderMapper.class); List<Order> list = orderMapper.listOrder(); for (Order u : list) { System.out.println(u); } sqlSession.close(); }
结果:
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