Mybatis_8动态sql之if where

　　　　1.动态sql

　　　　　　通过mybatis提供的各种标签方法实现动态拼接sql

　　如根据性别和名字查询用户。

User.xml

 1 
 2     <select id="selectUserBySexAndUserName"
 3         parameterType="com.me.mybatis.pojo.User"
 4         resultType="com.me.mybatis.pojo.User">
 5         select * from user
 6         where
 7         <if test="sex !=null and sex !=''">
 8             sex = #{sex}
 9         if>
10         <if test="username !=null and username !=''">
11             and username =#{username}
12         if>
13     select>

User.xml

UserMapper.java

 1 package com.me.mybatis.mapper;
 2 
 3 import java.util.List;
 4 
 5 import com.me.mybatis.pojo.QueryVo;
 6 import com.me.mybatis.pojo.User;
 7 
 8 public interface UserMapper {
 9         //遵循四个原则
10         //1.接口方法名==user.xml文件中的id名
11         //2.返回值类型与mapper.xml文件中的返回值类型要一致
12         //3.方法的入参类型与mapper.xml中入参的类型一致
13         //4.mapper.xml文件的namespace与接口绑定在一起
14         public User findUserById(Integer id);
15         public List findUserByQueryVo(QueryVo vo);
16         public Integer countUsers();
17         public List selectUserBySexAndUserName(User user);
18 }

User.java

测试文件：

  1 package com.me.mybatis.junit;
  2 
  3 import java.io.InputStream;
  4 import java.util.List;
  5 
  6 import org.apache.ibatis.io.Resources;
  7 import org.apache.ibatis.session.SqlSession;
  8 import org.apache.ibatis.session.SqlSessionFactory;
  9 import org.apache.ibatis.session.SqlSessionFactoryBuilder;
 10 import org.junit.jupiter.api.Test;
 11 
 12 import com.me.mybatis.mapper.OrderMapper;
 13 import com.me.mybatis.mapper.UserMapper;
 14 import com.me.mybatis.pojo.Orders;
 15 import com.me.mybatis.pojo.QueryVo;
 16 import com.me.mybatis.pojo.User;
 17 
 18 public class MybatisMapperTest {
 19 
 20     @Test
 21     void testMapper() throws Exception {
 22         // 加载核心配置文件
 23         String resource = "SqlMapConfig.xml";
 24         InputStream resourceAsStream = Resources.getResourceAsStream(resource);
 25         // 创建sqlsessionFactory
 26         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
 27         // 创建sqlsession
 28         SqlSession openSession = sqlSessionFactory.openSession();
 29         //sqlsession生成一个实现类
 30         UserMapper mapper = openSession.getMapper(UserMapper.class);
 31         //利用接口调方法
 32         User user = mapper.findUserById(10);
 33         System.out.println(user);
 34     }
 35     
 36     @Test
 37     void testQueryVo() throws Exception {
 38         // 加载核心配置文件
 39         String resource = "SqlMapConfig.xml";
 40         InputStream resourceAsStream = Resources.getResourceAsStream(resource);
 41         // 创建sqlsessionFactory
 42         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
 43         // 创建sqlsession
 44         SqlSession openSession = sqlSessionFactory.openSession();
 45         //sqlsession生成一个实现类
 46         UserMapper mapper = openSession.getMapper(UserMapper.class);
 47         //利用接口调方法
 48         QueryVo vo=new QueryVo();
 49         User user=new User();
 50         user.setUsername("五");
 51         vo.setUser(user);
 52         List u = mapper.findUserByQueryVo(vo);
 53         for (User user2 : u) {
 54             System.out.println(user2);
 55         }
 56     }
 57     //查询用户总数
 58     @Test
 59     void testCountUser() throws Exception {
 60         // 加载核心配置文件
 61         String resource = "SqlMapConfig.xml";
 62         InputStream resourceAsStream = Resources.getResourceAsStream(resource);
 63         // 创建sqlsessionFactory
 64         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
 65         // 创建sqlsession
 66         SqlSession openSession = sqlSessionFactory.openSession();
 67         //sqlsession生成一个实现类
 68         UserMapper mapper = openSession.getMapper(UserMapper.class);
 69         //利用接口调方法
 70         Integer users = mapper.countUsers();
 71 
 72             System.out.println(users);
 73         
 74     }
 75     //查询所有订单
 76     @Test
 77     void testFindAllOrders() throws Exception {
 78         // 加载核心配置文件
 79         String resource = "SqlMapConfig.xml";
 80         InputStream resourceAsStream = Resources.getResourceAsStream(resource);
 81         // 创建sqlsessionFactory
 82         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
 83         // 创建sqlsession
 84         SqlSession openSession = sqlSessionFactory.openSession();
 85         //sqlsession生成一个实现类
 86         OrderMapper mapper = openSession.getMapper(OrderMapper.class);
 87         //利用接口调方法
 88         List orders = mapper.findAllOrders();
 89         for (Orders orders2 : orders) {
 90             
 91             System.out.println(orders2);
 92         }
 93         
 94     }
 95     //根据姓名和性别查询
 96     @Test
 97     void testFindUserBySexAndName() throws Exception {
 98         // 加载核心配置文件
 99         String resource = "SqlMapConfig.xml";
100         InputStream resourceAsStream = Resources.getResourceAsStream(resource);
101         // 创建sqlsessionFactory
102         SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
103         // 创建sqlsession
104         SqlSession openSession = sqlSessionFactory.openSession();
105         //sqlsession生成一个实现类
106         UserMapper mapper = openSession.getMapper(UserMapper.class);
107         //利用接口调方法
108         User user=new User();
109         user.setSex("1");
110         user.setUsername("张小明");
111         List users = mapper.selectUserBySexAndUserName(user);
112         for (User user1 : users) {
113             
114             System.out.println(user1);
115         }
116         
117     }
118 
119 }

测试类

发现可以查询出来：

 

 

注释掉名字的set方法

 

 

发现爱你结果可以查五个用户

 

 

 

但是注释掉关于名字的set方法，则会报错

 

 

 

这时便可以用if where来解决问题，因为