一、延遲載入

1、在mybatis.xml配置檔案中，開啟延遲載入
    <settings>
        <!--開啟延遲載入-->
        <setting name="lazyLoadingEnabled" value="true"></setting>
        <setting name="aggressiveLazyLoading" value="false"></setting>
        <!--延遲載入觸發方法，equals、hashCode、toString都會觸發載入-->
        <setting name="
 
lazyLoadTriggerMethods" value="hashCode"></setting>
    </settings>
2、配置mapper檔案
    1、一對一
        * 一方
            <resultMap id="studentGradeById" type="Student">
                <id column="id" property="id"></id>
                <result column="name" property="name
 
"></result>
                <result column="age" property="age"></result>
                <result column="sex" property="sex"></result>
　　　　　　　　　 <!--關閉延遲載入會做兩次查詢-->
                <association column="grade_id" property="grade" javaType="Grade"
                             select
 
="com.wuxi.daos.GradeMapper.selectById"></association>
            </resultMap>
            <select id="selectStudentGradeById" resultMap="studentGradeById">
                select * from student where id = #{id}
            </select>
        * 另一方
            <select id="selectById" resultType="Grade">
                select * from grade where id = #{id}
            </select>
        * 測試
            Student student = smapper.selectStudentGradeById(4);
            System.out.println(student);
            // student.hashCode();
            System.out.println(student.getGrade());
    2、一對多
        * 一方
            <resultMap type="Grade" id="gradeStudents">
                <id column="id" property="id"></id>
                <result column="name" property="name"></result>
　　　　　　　　　 <!--關閉延遲載入會做兩次查詢-->
                <collection property="students" ofType="Student" column="id"
                            select="com.wuxi.daos.StudentMapper.selectStudentsByGrade"></collection>
            </resultMap>
            <select id="selectById" resultMap="gradeStudents">
                select * from grade where id = #{id}
            </select>
        * 多方
            <select id="selectStudentsByGrade" resultType="Student">
                select * from student where grade_id=#{grade_id}
            </select>
        * 測試
            Grade grade = gmapper.selectById(1);
            System.out.println(grade);
            // student.hashCode();
            System.out.println(grade.getStudents());

二、快取