package com.company.entity; 
import java.io.Serializable; 
import java.util.Date; 
public class Student implements Serializable{ 
private static final long serialVersionUID = 1L; 
private int id; 
private String name; 
private Date birth; 
private Group group; 
public Group getGroup() { 
return group; 
} 
public void setGroup(Group group) { 
this.group = group; 
} 
public int getId() { 
return id; 
} 
public void setId(int id) { 
this.id = id; 
} 
public String getName() { 
return name; 
} 
public void setName(String name) { 
this.name = name; 
} 
public Date getBirth() { 
return birth; 
} 
public void setBirth(Date birth) { 
this.birth = birth; 
} 
@Override 
public String toString() { 
return "Student [birth=" + birth + ", group=" + group + ", id=" + id 
+ ", name=" + name + "]"; 
} 
}

package com.company.entity; 
import java.util.List; 
public class Group { 
private int id; 
private String name; 
private String position; 
private List<Student> students; 
public List<Student> getStudents() { 
return students; 
} 
public void setStudents(List<Student> students) { 
this.students = students; 
} 
public int getId() { 
return id; 
} 
public void setId(int id) { 
this.id = id; 
} 
public String getName() { 
return name; 
} 
public void setName(String name) { 
this.name = name; 
} 
public String getPosition() { 
return position; 
} 
public void setPosition(String position) { 
this.position = position; 
} 
@Override 
public String toString() { 
return "Group [id=" + id + ", name=" + name + ", position=" + position 
+ "]"; 
} 
}

create table student(
id int primary key,
name varchar(20),
birth date,
group_id int references g_group(g_id));

create table g_group(
g_id int primary key,
g_name varchar(20),
g_position varchar(30));

create sequence student_id_sequence;
create sequence group_id_sequence;

<?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="com.company.dao.IStudentDAO"> 
<!-- mybatis緩存 --> 
<cache eviction="LRU" flushInterval="600000" size="1024" readOnly="false" /> 
<!-- sql標(biāo)簽用來定義一些可以被重用的sql語句或字段或片段等 --> 
<sql id="studentColumns">select id,name,birth from student</sql> 
<!-- 此處獲得多對一的關(guān)系 ,但就單條記錄而言卻是一對一的關(guān)系，所以一對一的寫法跟此相同--> 
<resultMap type="Student" id="getStudentAndGroup" > 
<id column="id" property="id"/> 
<result column="name" property="name"/> 
<result column="birth" property="birth"/> 
<association property="group" column="group_id" javaType="Group"> 
<id column="g_id" property="id"/> 
<result column="g_name" property="name"/> 
<result column="g_position" property="position"/> 
</association> 
</resultMap> 
<select id="many2one" resultMap="getStudentAndGroup" parameterType="int" > 
select s.id,s.name,s.birth,s.group_id,g.g_id,g.g_name,g.g_position 
from student s 
left join g_group g on s.group_id = g.g_id 
where s.id = #{id} 
</select> 
<!-- 意圖是獲得一個學(xué)生，并且獲得該學(xué)生所屬的組，跟上面的意思差不多 ,用association的select屬性--> 
<!-- 于上面的相比個人感覺上面的效率要高些，因?yàn)樯厦嬷挥幸粭lsql語句 --> 
<resultMap type="Student" id="getStudentAndGroupUseSelectMap"> 
<id column="id" property="id"/> 
<result column="name" property="name"/> 
<result column="birth" property="birth"/> 
<association property="group" column="group_id" javaType="Group" select="selectGroup" /> 
</resultMap> 
<select id="getStudentAndGroupUseSelect" resultMap="getStudentAndGroupUseSelectMap" parameterType="int"> 
select * 
from student 
where id = #{id} 
</select> 
<select id="selectGroup" resultType="Group" parameterType="int" flushCache="false" useCache="true"><!-- 此處實(shí)用緩存 --> 
select g_id as id, g_name as name, g_position as position 
from g_group 
where g_id = #{id} 
</select> 
<!-- 動態(tài)sql語句 的測試dynamic sql--> 
<select id="getStudentBySomeCondition" parameterType="Student" resultType="Student"> 
select * 
from student 
<where> 
<if test="id != null"> 
id>2 
</if> 
<if test="name != null"> 
and name like '%g%' 
</if> 
</where> 
</select> 
<!-- MyBatis調(diào)用存儲過程 --> 
<resultMap type="Student" id="studentMap"> 
<id column="id" property="id"/> 
<result column="name" property="name"/> 
<result column="birth" property="birth"/> 
</resultMap> 
<select id="getAllUser" statementType="CALLABLE" > 
{call get_all_student(#{students ,mode=OUT, jdbcType=CURSOR, javaType=ResultSet, resultMap=studentMap} )} 
</select> 
<!-- MyBatis向student表中插入一條數(shù)據(jù) --> 
<insert id="add" parameterType="Student" keyColumn="id"> 
<selectKey keyProperty="id" order="BEFORE" resultType="int"> 
select stu_id_sequence.nextval from dual 
</selectKey> 
insert into student(id,name,birth) values(#{id},#{name},#{birth}) 
</insert> 
<!-- 根據(jù)id獲得學(xué)生的信息 --> 
<select id="getById" parameterType="int" resultType="Student"> 
<include refid="studentColumns"/> where id=#{id} 
</select> 
<!-- 此處的實(shí)現(xiàn)方法是一個分頁的原型,請查看IStudentDAOImpl.java中的調(diào)用方法 --> 
<select id="getAllStudent" resultMap="studentMap"> 
<include refid="studentColumns"/> order by id<!--此處是引用了上面預(yù)定義好的sql語句--> 
</select> 
</mapper>