Mysql动态SQL

mysql动态SQL

解决

Error querying database.  Cause: org.apache.ibatis.executor.ExecutorException: A query was run and no Result Maps were found for the Mapped Statement 'com.zwt.mapper.AddressesMapper.queryTrim'.  It's likely that neither a Result Type nor a Result Map was specified.

的问题

在sql语句加上返回的类型 :

resultType="com.zwt.pojo.Addresses"

缓存

两次查询仅有一次调用SQL语句，第二次从缓存中命中。

SqlSession sqlSession = MybatisUtil.getSession();
AddressesMapper mapper = sqlSession.getMapper(AddressesMapper.class);
​
List<Addresses> addresses = mapper.listAll();
        System.out.println(addresses);
List<Addresses> addresses2 = mapper.listAll();
        System.out.println(addresses2);
        sqlSession.commit();
        sqlSession.close();

DEBUG [main] - ==> Preparing: select country,state,city from addresses DEBUG [main] - ==> Parameters: DEBUG [main] - <== Total: 7

 

缓存失效方式

查询后进行增删改会使缓存失效

SqlSession sqlSession = MybatisUtil.getSession(); 
AddressesMapper mapper = sqlSession.getMapper(AddressesMapper.class);
List<Addresses> addresses = mapper.listAll();
//缓存失效一：查询后增删改会使缓存失效 
Addresses a = new Addresses(); 
a.setId(2); 
a.setCountry("2"); 
a.setCity("3"); 
a.setState("4"); 
a.setZip("5"); 
mapper.update(a); 
List<Addresses> addresses2 = mapper.listAll(); 
sqlSession.commit(); 
sqlSession.close();

DEBUG [main] - ==> Preparing: select country,state,city from addresses DEBUG [main] - ==> Parameters: DEBUG [main] - <== Total: 7 DEBUG [main] - ==> Preparing: update addresses SET country = ?, city = ?, state = ?, zip = ? WHERE id = ? DEBUG [main] - ==> Parameters: 2(String), 3(String), 4(String), 5(String), 2(Long) DEBUG [main] - <== Updates: 1 DEBUG [main] - ==> Preparing: select country,state,city from addresses DEBUG [main] - ==> Parameters:

强制清空缓存

List<Addresses> addresses = mapper.listAll();
//强制清空会话所有缓存sqlSession.clearCache();
List<Addresses> addresses2 = mapper.listAll();
sqlSession.commit();
sqlSession.close();

DEBUG [main] - ==> Preparing: select country,state,city from addresses DEBUG [main] - ==> Parameters: DEBUG [main] - <== Total: 7 DEBUG [main] - ==> Preparing: select country,state,city from addresses DEBUG [main] - ==> Parameters: DEBUG [main] - <== Total: 7

 

动态SQL

动态SQL-if

<select id="queryByCountryCity" resultType="com.zwt.pojo.Addresses">    
    select * from addresses 
    <where> 
    <if test="country != null and city = '' "> and COUNTRY = #{country}</if>                   
<if test="city != null">and city = #{city}</if>                            
</where>
</select>

public void m3(){        
    SqlSession sqlSession = MybatisUtil.getSession();        
    AddressesMapper mapper = sqlSession.getMapper(AddressesMapper.class);//                 
List<Addresses> addresses = mapper.queryByCountryCity(null, "Perry");//                 
List<Addresses> addresses = mapper.queryByCountryCity("China", null);                   
List<Addresses> addresses = mapper.queryByCountryCity("Taylor", "");                    
System.out.println(addresses);        
    sqlSession.close();

 

当country不为空并且city为空时，通过country查询；

当city不为空时则通过city查询

动态SQL-模糊查询

第一种

在应用程序层面加入%：

List<Addresses> addresses = mapper.queryLike("%Luo%");
select * from addresses where city like  #{city}

第二种

通过mysql的函数 concat 完成：

select * from addresses where city like concat('%', #{city}, '%')

第二种

通过band标签对变量重新绑定，在用新的变量查询

<bind name = "_city" value = " '%' + city + '%'"></bind>
select * from addresses where city like  #{_city}