一、Mybatis学习。

（1）MyBatis的多表操作。

（1.1）一对一查询。

第1种映射OrderMapper.xml文件：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="mapper.OrderMapper">
    <resultMap id="orderMap" type="domain.Order">
        <!--手动指定字段与实体属性的映射关系
            column:数据表的字段名称
            property：实体的属性名称
        -->
        <id column="oid" property="id"></id><!--因为数据库多表查询的两个表都有id-->
        <result column="ordertime" property="ordertime"></result>
        <result column="total" property="total"></result>
        <result column="uid" property="user.id"></result>
        <result column="username" property="user.username"></result>
        <result column="password" property="user.password"></result>
        <result column="birthday" property="user.birthday"/>
    </resultMap>
    <select id="findAll" resultMap="orderMap">
        select *,o.id oid from orders o,user u where o.uid = u.id
    </select>
</mapper>

第2种映射OrderMapper.xml文件：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="mapper.OrderMapper">
    <resultMap id="orderMap" type="domain.Order">
        <!--手动指定字段与实体属性的映射关系
            column:数据表的字段名称
            property：实体的属性名称
        -->
        <id column="oid" property="id"></id><!--因为数据库多表查询的两个表都有id-->
        <result column="ordertime" property="ordertime"></result>
        <result column="total" property="total"></result>
        <!--association标签属性：
            property：当前实体（order）中的属性名称（private User user）user
            javaType：当前实体(order)中的属性的类型(User)
        -->
        <association property="user" javaType="domain.User">
            <id column="uid" property="id"></id>
            <result column="username" property="username"></result>
            <result column="password" property="password"></result>
            <result column="birthday" property="birthday"></result>
        </association>
    </resultMap>
    <select id="findAll" resultMap="orderMap">
        select *,o.id oid from orders o,user u where o.uid = u.id
    </select>
</mapper>

（1.2）一对多查询。

映射UserMapper.xml文件：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="mapper.UserMapper">
    <!--一对多查询的配置-->
    <resultMap id="userMap" type="domain.User">
        <!--user的信息-->
        <id column="uid" property="id"/>
        <result column="username" property="username"/>
        <result column="password" property="password"/>
        <result column="birthday" property="birthday"/>
        <!--配置集合信息:
                property：集合名称
                ofType：当前集合中的数据类型
        -->
        <collection property="orderList" ofType="domain.Order">
            <!--封装order的数据-->
            <id column="oid" property="id"/>
            <result column="ordertime" property="ordertime"/>
            <result column="total" property="total"/>
        </collection>
    </resultMap>
    <select id="findAll" resultMap="userMap">
        select *,o.id oid from user u,orders o where u.id = o.id
    </select>
</mapper>

（1.3）多对多查询。

映射UserMapper.xml文件：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="mapper.UserMapper">
    <resultMap id="userRoleMap" type="domain.User">
        <!--user的信息-->
        <id column="userid" property="id"/>
        <result column="username" property="username"/>
        <result column="password" property="password"/>
        <result column="birthday" property="birthday"/>
        <collection property="roleList" ofType="domain.Role">
            <!--user内部的roleList信息-->
            <id column="roleid" property="id"/>
            <result column="roleName" property="roleName"/>
            <result column="roleDesc" property="roleDesc"/>
        </collection>
    </resultMap>
    <!--多对多的查询配置-->
    <select id="findUserAndRole" resultMap="userRoleMap">
        select * from user u,sys_user_role ur,sys_role r where u.id = ur.userid and ur.roleid = r.id
    </select>
</mapper>