mybatis高级查询

sqlSession的获取

SqlSessionFactoryBean bean = new SqlSessionFactoryBean();
bean.setDataSource(mysqlDataSource());
bean.setConfigLocation(new PathMatchingResourcePatternResolver().getResource("classpath:mybatis/mybatis-config.xml"));
bean.setMapperLocations(new PathMatchingResourcePatternResolver().getResources("classpath:mapper/mysql/*.xml"));
bean.setTypeAliasesPackage("com.getword.entity");
sqlSessionFactory = bean.getObject();

one to one

方式一

假设user和role是一对一关系，中间表为Sys_user_role

public class SysUser{
    private SysRole role;
    ...
}

<select id="findUserAndRoleById" resultType="SysUser">
    select
    u.id,
    u.userName userName,
    u.userPassword userPassword,
    r.id "role.id",
    r.roleName "role.roleName"
    from sys_user u
    inner join sys_user_role ur on u.id=ur.userId
    inner join sys_role r on r.id = ur.roleId
    where u.id = #{id}
</select>

方式二

使用resultmap，和第一种方式类似

<resultMap id="userRoleMap" type="SysUser">
    <id property="id" column="id" />
    <result property="userName" column="userName" />
    <result property="userPassword" column="userPassword" />
    <result property="role.id" column="roleId" />
    <result property="role.roleName" column="roleName" />
</resultMap>
<select id="findUserAndRoleById" resultMap="userRoleMap">
    select
    u.id,
    u.userName userName,
    u.userPassword userPassword,
    r.id roleId,
    r.roleName roleName
    from sys_user u
    inner join sys_user_role ur on u.id=ur.userId
    inner join sys_role r on r.id = ur.roleId
    where u.id = #{id}
</select>

方式三，association一一对应

此种方式，对于多表查询，只会封装指定的result标签的字段

<resultMap id="userRoleMap" type="SysUser">
    <id property="id" column="id" />
    <result property="userName" column="userName" />
    <result property="userPassword" column="userPassword" />
    <association property="role" columnPrefix="role" javaType="SysRole">
        <result property="id" column="Id" />
        <result property="roleName" column="Name" />
    </association>
</resultMap>
<select id="findUserAndRoleById" resultMap="userRoleMap">
    select
    u.id,
    u.userName userName,
    u.userPassword userPassword,
    r.id roleId,
    r.roleName roleName
    from sys_user u
    inner join sys_user_role ur on u.id=ur.userId
    inner join sys_role r on r.id = ur.roleId
    where u.id = #{id}
</select>

resultMap可以继承

<resultMap id="userRoleMap" type="SysUser" extends="userMap">
    <result property="userPassword" column="userPassword" />
    <association property="role" columnPrefix="role" javaType="SysRole">
        <result property="id" column="Id" />
        <result property="roleName" column="Name" />
    </association>
</resultMap>
<select id="findUserAndRoleById" resultMap="userRoleMap">
    select
    u.id,
    u.userName userName,
    u.userPassword userPassword,
    r.id roleId,
    r.roleName roleName
    from sys_user u
    inner join sys_user_role ur on u.id=ur.userId
    inner join sys_role r on r.id = ur.roleId
    where u.id = #{id}
</select>

方式四，association嵌套查询，最简单的方式

<resultMap id="userMap" type="SysUser">
    <id property="id" column="id" />
    <result property="userName" column="userName" />
</resultMap>

<resultMap id="userRoleMap" type="SysUser" extends="userMap">
    <result property="userPassword" column="userPassword" />
    <association property="role" column="roleId" select="com.getword.dao.SysRoleDao.findById" />
</resultMap>
<select id="findUserAndRoleById" resultMap="userRoleMap">
    select
    u.id,
    u.userName userName,
    u.userPassword userPassword,
    r.id roleId
    from sys_user u
    inner join sys_user_role ur on u.id=ur.userId
    inner join sys_role r on r.id = ur.roleId
    where u.id = #{id}
</select>

简写

<resultMap id="userRoleMap" type="SysUser">
    <result property="userPassword" column="userPassword" />
    <association property="role" column="roleId" select="com.getword.dao.SysRoleDao.findById" />
</resultMap>
<select id="findUserAndRoleById" resultMap="userRoleMap">
    select
    *
    from sys_user u
    inner join sys_user_role ur on u.id=ur.userId
    where u.id = #{id}
</select>

one to many

方式一

<resultMap id="userMap" type="SysUser">
    <id property="id" column="id" />
    <result property="userName" column="userName" />
    <result property="userPassword" column="userPassword" />
</resultMap>

<resultMap id="userRoleMap" type="SysUser" extends="userMap">
    <collection property="roles" javaType="SysRole" columnPrefix="role">
        <id property="id" column="Id" />
        <result property="roleName" column="Name" />
    </collection>
</resultMap>
<select id="findUserAndRoleById" resultMap="userRoleMap">
    select
    u.id,
    u.userName userName,
    u.userPassword userPassword,
    r.id roleId,
    r.roleName roleName
    from sys_user u
    inner join sys_user_role ur on u.id=ur.userId
    inner join sys_role r on r.id = ur.roleId
    where u.id = #{id}
</select>

对于id相同的user被归为一个user，相当于分组了

转载于:https://www.cnblogs.com/zhuxiang1633/p/11532123.html