【MyBatis学习18】使用注解配置Mapper

本文博客地址：http://blog.csdn.net/soonfly/article/details/67640653 （转载请注明出处）

MyBatis支持使用注解来配置映射的sql语句，这样可以省掉映射器xml文件。

一、映射语句

1、insert
比如入门实例中的：

public int insert(User user) throws Exception;

<insert id="insert"  parameterType="twm.mybatisdemo.pojo.User" useGeneratedKeys="true" keyProperty="id">
    
    insert into user (username,address,email) values (#{username},#{address},#{email})
insert>

改成注解来配置映射：

@Insert("insert into user (username,address,email) values (#{username},#{address},#{email})")
@Options(useGeneratedKeys = true, keyProperty = "id") 
public int insert(User user) throws Exception;

这里使用@Insert注解来定义一个INSERT映射语句。
并且使用@Options注解的userGeneratedKeys 和keyProperty属性，让数据库auto_increment生成的主键值，赋值到keyProperty标记的属性id中

还有一种获取主键的方法（oracle要用SELECT SEQ.NEXTVAL FROM DUAL ，且order设为before）

<insert id="insert"  parameterType="twm.mybatisdemo.pojo.User" >
    
    <selectKey keyProperty="id" order="AFTER" resultType="java.lang.Integer">
           select last_insert_id()
    selectKey>
    insert into user (username,address,email) values (#{username},#{address},#{email})
insert>

相应的注解是：

@Insert("insert into user (username,address,email) values (#{username},#{address},#{email})")
@SelectKey(statement="select last_insert_id()",keyProperty="id", resultType=int.class, before=true)
public int insert(User user) throws Exception;

2、select

@Select("select * from user where id=#{id}")
public User selectById(int id) throws Exception;

返回的是一个User对象，因此如果select语句返回多行记录，就会出现TooManyResultsException异常。

3、update

@Update("update user set username=#{username},address=#{address},email=#{email} where id=#{id}")
public int update(User user) throws Exception;

4、delete

@Delete("delete from user where id=#{id}")
public int delete(int id) throws Exception;

二、结果映射

在xml配置文件中，将查询结果和JavaBean属性映射起来的标签是。对应的是@Results注解

@Select("select * from user")
@Results({ @Result(id = true, column = "id", property = "id"),
        @Result(column = "username", property = "user_name"),
        @Result(column = "city", property = "city") })
public List selectAll() throws Exception;

@Results注解没办法复用。譬如我们的public User selectById(int id) throws Exception也要用到同样的@Results注解，但还是要重新写一个一模一样的@Results

@Select("select * from user where id=#{id}")
@Results({ @Result(id = true, column = "id", property = "id"),
        @Result(column = "username", property = "user_name"),
        @Result(column = "city", property = "city") })
public User selectById(int id) throws Exception;

如果要想使用可以复用的映射器，那么就使用@ResultMap注解。该注解依赖一个xml配置文件。
在接口文件同目录下新建一个userMapper.xml文件，并定义一个名为userMap的resultMap。

<mapper namespace="twm.mybatisdemo.mapper.UserMapper">
    
    <resultMap id="userMap" type="twm.mybatisdemo.pojo.User">
        <id column="id" property="id" jdbcType="INTEGER" />
        <result property="user_name" column="username">result>
        <result property="city" column="city">result>
    resultMap>
mapper>

在userMapper.java中，使用@ResultMap引用名为userMap的resultMap，实现复用。

@Select("select * from user where id=#{id}")  
@ResultMap("twm.mybatisdemo.mapper.UserMapper.userMap")  
public User selectById(int id) throws Exception;

@Select("select * from user")  
@ResultMap("twm.mybatisdemo.mapper.UserMapper.userMap")  
public List selectAll() throws Exception;

三、关联关系

1、一对一关系
MyBatis提供了@One注解来配合@Result注解，从而实现一对一关联查询数据的加载。
比如所有user对象都有个配偶信息spouse(本例中配偶本身也是一个user对象)

@Select("select * from user")
@Results({ @Result(id = true, column = "id", property = "id"),
        @Result(column = "username", property = "user_name"),
        @Result(column = "city", property = "city"),
        @Result(column = "account_id", property = "account",one = @One(select = "twm.mybatisdemo.mapper.AccountMapper.selectById")) })
public List selectAll() throws Exception;

在这里column = "account_id"指定了向twm.mybatisdemo.mapper.AccountMapper.selectById方法传递的参数。如果@OneSELECT查询返回了多行结果，则会抛出TooManyResultsException异常。

调用:

UserMapper userMapper =sqlSession.getMapper(UserMapper.class);  
List userlist = userMapper.selectAll();  
System.out.println(userlist[0].getAccount().getBalance()); 

如果结果映射使用的是xml文件,那么可以association 来配置映射：

<mapper namespace="twm.mybatisdemo.mapper.UserMapper">
    
    <resultMap id="userMapWithAccount" type="twm.mybatisdemo.pojo.User">
        <id column="id" property="id" jdbcType="INTEGER" />
        <result property="user_name" column="username">result>
        <result property="city" column="city">result>
        <association property="account" javaType="Account" column="account_id" 
            select="twm.mybatisdemo.mapper.AccountMapper.selectById" />
    resultMap>
mapper>

接口如下：

@Select("select * from user")
@ResultMap("twm.mybatisdemo.mapper.UserMapper.userMapWithAccount")
public List selectAll() throws Exception;

2、一对多关系
MyBatis提供了@Many注解来配合@Result注解，从而实现一对多关联查询数据的加载。
现在让我们看一下如何使用@Many注解获取一个讲师及其教授课程列表信息：

public interface TutorMapper
{
    @Select("select * from courses where tutor_id=#{tutorId}")
    @Results(
    {
        @Result(id = true, column = "course_id", property = "courseId"),
        @Result(column = "name", property = "name"),
        @Result(column = "description", property = "description"),
        @Result(column = "start_date" property = "startDate"),
        @Result(column = "end_date" property = "endDate")
    })
    List findCoursesByTutorId(int tutorId);

    @Select("SELECT tutor_id, name as tutor_name, email, addr_id
            FROM tutors where tutor_id=#{tutorId}")
    @Results(
    {
        @Result(id = true, column = "tutor_id", property = "tutorId"),
        @Result(column = "tutor_name", property = "name"),
        @Result(column = "email", property = "email"),
        @Result(property = "address", column = "addr_id",
        one = @One(select = " com.mybatis3.
        mappers.TutorMapper.findAddressById")),
        @Result(property = "courses", column = "tutor_id",
        many = @Many(select = "com.mybatis3.mappers.TutorMapper.
        findCoursesByTutorId"))
    })
    Tutor findTutorById(int tutorId);
}

同样也可以采用配置xml中配置resultMaps的方式

"com.mybatis3.mappers.TutorMapper">
    "Course" id="CourseResult">
        <id column="course_id" property="courseId" />
        <result column="name" property="name" />
        <result column="description" property="description" />
        <result column="start_date" property="startDate" />
        <result column="end_date" property="endDate" />
    
    "Tutor" id="TutorResult">
        <id column="tutor_id" property="tutorId" />
        <result column="tutor_name" property="name" />
        <result column="email" property="email" />
        property="courses" resultMap="CourseResult" />
    

public interface TutorMapper
{
    @Select("SELECT T.TUTOR_ID, T.NAME AS TUTOR_NAME, EMAIL,
            A.ADDR_ID, STREET, CITY, STATE, ZIP, COUNTRY, COURSE_ID, C.NAME,
            DESCRIPTION, START_DATE, END_DATE  FROM TUTORS T LEFT OUTER
            JOIN ADDRESSES A ON T.ADDR_ID=A.ADDR_ID LEFT OUTER JOIN COURSES
            C ON T.TUTOR_ID=C.TUTOR_ID WHERE T.TUTOR_ID=#{tutorId}")
    @ResultMap("com.mybatis3.mappers.TutorMapper.TutorResult")
    Tutor selectTutorById(int tutorId);
}

四、动态SQL

MyBatis提供了各种注解如@InsertProvider,@UpdateProvider,@DeleteProvider和@SelectProvider，来帮助构建动态SQL语句，然后让MyBatis执行这些SQL语句。

这里重点用@SelectProvider举例：

创建一个TutorDynaSqlProvider.java类，以及findTutorByIdSql()方法，如下所示：

package com.mybatis3.sqlproviders;
import org.apache.ibatis.jdbc.SQL;
public class TutorDynaSqlProvider
{
    public String findTutorByIdSql(int tutorId)
    {
        return "SELECT TUTOR_ID AS tutorId, NAME, EMAIL FROM TUTORS
               WHERE TUTOR_ID=" + tutorId;
    }
}

在TutorMapper.java接口中创建一个映射语句，如下：

@SelectProvider(type=TutorDynaSqlProvider.class, method="findTutorByIdSql")  
Tutor findTutorById(int tutorId);  

本文博客地址：http://blog.csdn.net/soonfly/article/details/67640653 （转载请注明出处）