<MyBatis>入门五 查询的返回值处理

    /**
     * 返回List集合
     */
    List<Employee> getEmpsByNameLike(String name);

    <!--如果返回的是集合，resultType需要写集合中元素的类型-->
    <select id="getEmpsByNameLike" resultType="org.maple.pojo.Employee">
        SELECT id,last_name name,email,gender
        FROM tbl_employee
        WHERE last_name like concat(‘%‘,#{name},‘%‘);
    </select>

Employee{id=1, name=‘tom‘, gender=0, email=‘tom@atguigu.com‘}
Employee{id=8, name=‘rose‘, gender=1, email=‘rose@qq.com‘}
Employee{id=9, name=‘zhaozhihao‘, gender=1, email=‘chenquan@qq.com‘}
Employee{id=12, name=‘nihao‘, gender=1, email=‘nihao@qq.com‘}

    /**
     * 返回一条记录map,key就是列名，值就是表中的值
     */
    Map<String,Object> getEmpByIdReturnMap(Integer id);

    <!--如果返回的是map，resultType需要写map,mybatis为常用类起了别名-->
    <select id="getEmpByIdReturnMap" resultType="map">
        SELECT id,last_name name,email,gender
        FROM tbl_employee
        WHERE id = #{id}
    </select>

{gender=0, name=tom, id=1, email=tom@atguigu.com}

    /**
     * 多条记录封装Map,Map<Integer,Employee>
     * @MapKey 告诉mybaits使用哪个属性封装成map的key
     */
    @MapKey("id")
    Map<Integer,Employee> getEmpByNameLikeReturnMap(String name);

    <!--如果返回的是map，封装成emp,resultType需要写Employee-->
    <select id="getEmpByNameLikeReturnMap" resultType="org.maple.pojo.Employee">
        SELECT id,last_name name,email,gender
        FROM tbl_employee
        WHERE last_name like concat(‘%‘,#{name},‘%‘);
    </select>

{1=Employee{id=1, name=‘tom‘, gender=0, email=‘tom@atguigu.com‘}, 
8=Employee{id=8, name=‘rose‘, gender=1, email=‘rose@qq.com‘}, 
9=Employee{id=9, name=‘zhaozhihao‘, gender=1, email=‘chenquan@qq.com‘}, 
12=Employee{id=12, name=‘nihao‘, gender=1, email=‘nihao@qq.com‘}}

    /**
     * 根据id查询员工
     */
    Employee getEmpById(Integer id);

<mapper namespace="org.maple.mapper.EmployeeMapperPlus">

    <!--resultMap 自定义封装规则-->
    <!--
        id:唯一id,方便引用
        type:自定义规则的java类型
    -->
    <resultMap id="MyEmp" type="org.maple.pojo.Employee">
        <!--
            id 主键的封装规则,底层会有优化
            column 数据库中字段
            property javaBean中的字段
        -->
        <id column="id" property="id"/>
        <result column="last_name" property="name"/>
        <!--其他不指定的列，如果名字一样，会自动封装。但是写resultMap建议都写上-->
        <result column="email" property="email"/>
        <result column="gender" property="gender"/>
    </resultMap>

    <!--简单的使用resultMap-->
    <select id="getEmpById" resultMap="MyEmp">
        SELECT id,last_name,email,gender
        FROM tbl_employee
        WHERE id = #{id}
    </select>

</mapper>

public class Employee {

    private Integer id;

    private String name;

    private Character gender;

    private String email;

    private Department dept;
}

public class Department {

    private Integer id;
    private String deptName;
}

    /**
     * 根据id查出员工和部门信息
     */
    Employee getEmpAndDeptById(Integer id);

　　<!--1.级联属性的方式-->

   <resultMap id="myEmpAndDept" type="org.maple.pojo.Employee">
        <id column="id" property="id"/>
        <result column="last_name" property="name"/>
        <result column="email" property="email"/>
        <result column="gender" property="gender"/>
        <result column="did" property="dept.id"/>
        <result column="deptName" property="dept.deptName"/>
    </resultMap>

    <select id="getEmpAndDeptById" resultMap="myEmpAndDept">
        SELECT e.id,e.last_name,e.email,e.gender,d.id did,d.dept_name deptName
        FROM tbl_employee e
                 INNER JOIN tbl_dept d
                            ON e.d_id = d.id
        WHERE e.id = #{id}
    </select>

    <!--2.使用association-->
    <resultMap id="myEmpAndDept2" type="org.maple.pojo.Employee">
        <id column="id" property="id"/>
        <result column="last_name" property="name"/>
        <result column="email" property="email"/>
        <result column="gender" property="gender"/>
        <association property="dept" javaType="org.maple.pojo.Department">
            <id column="did" property="id"/>
            <result column="deptName" property="deptName"/>
        </association>
    </resultMap>

    /**
     * 根据id查出员工和部门信息，分部查询
     */
    Employee getEmpAndDeptByIdStep(Integer id);

    <!--使用association进行分布查询-->
    <resultMap id="myEmpAndDeptStep" type="org.maple.pojo.Employee">
        <id column="id" property="id" />
        <result column="last_name" property="name"/>
        <result column="email" property="email"/>
        <result column="gender" property="gender"/>
        <!--property:Employee中的属性
            select:调用DepartmentMapper中的查询方法 命名空间+方法
            column:传给select 方法哪个参数
        -->
        <association property="dept" select="org.maple.mapper.DepartmentMapper.getDeptById" column="d_id"/>
    </resultMap>

    <select id="getEmpAndDeptByIdStep" resultMap="myEmpAndDeptStep">
        select id,last_name,gender,email,d_id from tbl_employee where id = #{id}
    </select>

     <settings>
             <setting name="lazyLoadingEnabled" value="true"/>
            <setting name="aggressiveLazyLoading" value="false"/> 
     </settings>

public class Department {

    private Integer id;
    private String deptName;
    private List<Employee> emps;
}

    /**
     * 根据id查询部门信息和所有员工
     */
    Department getDeptAndEmpsById(Integer id);

    <!-- 要通过id查询部门信息和所有员工 -->
    <resultMap id="myDept" type="org.maple.pojo.Department">
        <id column="id" property="id"/>
        <result column="dept_name" property="deptName"/>
        <!--定义集合时，使用collection属性-->
        <collection property="emps" ofType="org.maple.pojo.Employee">
            <id column="eId" property="id"/>
            <result column="last_name" property="name"/>
            <result column="gender" property="gender"/>
            <result column="email" property="email"/>
        </collection>
    </resultMap>

    <select id="getDeptAndEmpsById" resultMap="myDept">
        SELECT d.id,d.dept_name,e.id eId,e.last_name,e.gender,e.email
        FROM tbl_dept d
                 LEFT JOIN tbl_employee e
                           ON d.id = e.d_id
        WHERE d.id = #{id}
    </select>

    /**
     * 根据id 分部查询出部门信息和所有员工
     */
    Department getDeptAndEmpsByIdStep(Integer id);

    <!--分部查询-->
    <resultMap id="myDeptStep" type="org.maple.pojo.Department">
        <id column="id" property="id"/>
        <result column="dept_name" property="deptName"/>
        <collection property="emps" select="org.maple.mapper.EmployeeMapper.findEmpsById" column="id"></collection>
    </resultMap>
    
    <select id="getDeptAndEmpsByIdStep" resultMap="myDeptStep">
        SELECT id,dept_name
        FROM tbl_dept
        WHERE id = #{id}
    </select>