一、延迟加载
1、在mybatis.xml配置文件中，开启延迟加载
<settings>
<!--开启延迟加载-->
<setting name="lazyLoadingEnabled" value="true"></setting>
<setting name="aggressiveLazyLoading" value="false"></setting>
<!--延迟加载触发方法，equals、hashCode、toString都会触发加载-->
<setting name="lazyLoadTriggerMethods" value="hashCode"></setting>
<!--数据库下划线（_）命名转驼峰命名-->
<setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>
2、配置mapper文件
1、一对一
* 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> <!--关闭延迟加载会做两次查询-->
<association column="grade_id" property="grade" javaType="Grade"
select="com.wuxi.daos.GradeMapper.selectById"></association>
</resultMap>
<select id="selectStudentGradeById" resultMap="studentGrade<mark>本文来源gaodaimacom搞#代%码@网-</mark>ById">
select * from student where id = #{id}
</select>
* 另一方
<select id="selectById" resultType="Grade">
select * from grade where id = #{id}
</select>
* 测试
Student student = smapper.selectStudentGradeById(4);
System.out.println(student);
// student.hashCode();
System.out.println(student.getGrade());
2、一对多
* 一方
<resultMap type="Grade" id="gradeStudents">
<id column="id" property="id"></id>
<result column="name" property="name"></result> <!--关闭延迟加载会做两次查询-->
<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>
* 测试
Grade grade = gmapper.selectById(1);
System.out.println(grade);
// student.hashCode();
System.out.println(grade.getStudents());
二、缓存
1、一级缓存
1、概念
一级缓存是SqlSession范围的缓存，当调用SqlSession的修改，添加，删除，commit()，close()等方法时，就会清空一级缓存。
2、测试
// Student student1 = smapper.selectStudentGradeById(1);
// Student student2 = smapper.selectStudentGradeById(1);
// System.out.println(student1 == student2); // true
// ********************************
Student student1 = smapper.selectStudentGradeById(1);
Student student = new Student();
student.setName(“杜兰特”);
student.setAge(28);
student.setSex(1);
smapper.insertStudent(student);
Student student2 = smapper.selectStudentGradeById(1);
System.out.println(student1 == student2); // false
转载请注明原文链接：Mybatis如何实现延迟加载及缓存
