MybatisSQL语句动态查询,传入有值,数据库有值,数据查不出来。

Question

图1

图2

代码如下
private RoleService roleService;

private AdminUserRoleService adminUserRoleService;

@Before
public void befor() {
    ApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:/spring/spring-content.xml");
    this.roleService = applicationContext.getBean(RoleService.class);
    this.adminUserRoleService = applicationContext.getBean(AdminUserRoleService.class);
}
@Test  
public void test() {  
        List<AdminUserRole> adminUserRoleList =              
            adminUserRoleService.queryByField("role_id",""+19);
        System.out.println(adminUserRoleList.size());      
}  

映射文件

   <select id="queryByField" resultMap="adminUserRole" >
    SELECT *
    FROM wady_admin_user_role
    WHERE #{0} = #{1}
    </select>
    
    

求解疑惑，为什么SQL能在MySql里面查询,java里面就查不出来
——补充——

<select id="queryByField" resultMap="adminUserRole" >
    SELECT 
         <include refid="Base_Column_List" />
    FROM wady_admin_user_role
    WHERE #{0} =19
</select>

<select id="queryByField" resultMap="adminUserRole" >
    SELECT 
         <include refid="Base_Column_List" />
    FROM wady_admin_user_role
    WHERE role_id =#{1}
</select>

问题应该是， Mybatis的SQL语句查询的列为什么不能通过传入参数代替

Answer 1

<select id="queryByField" resultMap="adminUserRole" parameterType="String">
    SELECT 
         <include refid="Base_Column_List" />
    FROM wady_admin_user_role
    WHERE #{fieldName} = #{fieldValue}
</select>

找到Dao层 该方法通过注解可以实现

List<T> queryByField((@Param("fieldName")String fieldName,(@Param("fieldValue")String
fieldValue);
还有更简单方便快捷的,欢迎回复,修改答案

Answer 2

用 '#{}' 是预编译了, 字段名可以用 '${}' 提前拼接好

Answer 3

用字段拼接的方式，把#号改成
用#是走了预编译，你传过去的对于数据库来说都是参数值还不是字段，你这个需要拼接sql，所以用$,底层就是jdbc的statement