mybatis接口用法

1、注意要点

1 namespace与接口全限定名一致
2 id和抽象函数保持一致
3 参数类型与返回类型保持一致
4 java类名与xml文件名保存一致

举例

public interface GoodsMapper {
    Goods selectGoodsById();
    int insertGoods(Goods goods);
}

<mapper namespace="com.study.mapper.GoodsMapper"><!--命名空间-->
    <select id="selectGoodsById" resultType="com.study.entity.Goods">
        select * from goods where gid=4
    </select>
    <insert id="insertGoods" parameterType="com.study.entity.Goods">
        INSERT INTO Goods(gname,gprice,num,description,good_type,create_time)
        VALUES (#{gname},#{gprice},#{num},#{description},#{goodtype},now())
    </insert>
</mapper>

public class GoodsMapperTest {
    SqlSessionFactory factory;
    SqlSession sqlSession;

    @Before//在方法前执行
    public void setUp() {
        try {
            InputStream is= Resources.getResourceAsStream("mybatis-config.xml");//获取主配置文件
            factory=new SqlSessionFactoryBuilder().build(is);//创建工厂对象
            sqlSession = factory.openSession(true);//获取SqlSession（相当于Connection）
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @After//在方法执行后执行
    public void tearDown() {
        sqlSession.close();
    }

    @Test
    public void selectGoodsById() throws Exception {
        GoodsMapper mapper = sqlSession.getMapper(GoodsMapper.class);
        Goods goods = mapper.selectGoodsById();
        System.out.println(goods);
    }

    @Test
    public void insertGoods() throws Exception {
        GoodsMapper mapper = sqlSession.getMapper(GoodsMapper.class);
        Goods goods = new Goods("lenovo", new BigDecimal(5000), "lianxiang", 200, 1);
        mapper.insertGoods(goods);
    }
}

mybatis-config.xml配置

创建一个db.properties文件，内容如下：

jdbc.driverClass=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql:///taobao?useUnicode=true&characterEncoding=utf-8
jdbc.user=root
jdbc.password=123

<!--加载配置文件-->
    <properties resource="db.properties"/>

配置log4j日志，内容如下：

# Global logging configuration
log4j.rootLogger=ERROR, stdout
# MyBatis logging configuration...
log4j.logger.com.study.mapper=TRACE
# Console output...
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p [%t] - %m%n

<settings>
    <!-- 日志的实现类，可以不写，会自动匹配 -->
    <setting name="logImpl" value="LOG4J"/>
    <!-- 将数据库字段的下划线自动转为驼峰命名 -->
    <setting name="mapUnderscoreToCamelCase" value="true"/>
    <!-- 自动映射，FULL表示无论是否关联都进行自动映射 -->
    <setting name="autoMappingBehavior" value="FULL"/>
</settings>

别名

<!-- 指定包下面的所有实体类都会将类名作为别名 -->
<typeAliases>
    <package name="com.study.entity"/>
</typeAliases>

<!-- 使用的使用直接使用别名Goods，不用写全限定名 -->
<select id="selectGoodsById" resultType="Goods">
    select * from goods where gid=4
</select>

输出映射

resultType

当数据库字段与属性名一致时使用

resultMap

1、解决数据库字段与属性名不一致

2、关联（可以使用别名来解决）

注意：resultType与resultMap不能同时使用！

关联

关联结果 resultMap与resultMap嵌套

public class Goods {
        private GoodType goodsType;//属性是pojo 普通的java对象
    }

<select id="selectGoodsById" resultMap="goodsResultMap">
        SELECT * FROM goods g INNER JOIN data_dictionary d ON g.good_type=d.value_id WHERE d.type_code='good_type' AND gid=4
    </select>

    <resultMap id="goodsResultMap" type="Goods">
        <id property="gid" column="gid"/>
        <!--关联结果-->
        <association property="goodsType"  resultMap="goodTypeResultMap"/>
    </resultMap>

    <resultMap id="goodTypeResultMap" type="GoodType"/>

注意：resultMap的id和association的resultMap应该保持一致，resultMap中的type="GoodType"，GoodType为创建的类

关联查询 resultMap与select嵌套

<resultMap id="goodsResultMap" type="Goods">
        <id property="gid" column="gid"/>
        <!--关联结果-->
        <association property="goodsType" select="selectGoodType" column="good_type" javaType="GoodType"/>
    </resultMap>
    <select id="selectGoodsById" resultMap="goodsResultMap">
        SELECT * FROM goods WHERE gid=6
    </select>
    <select id="selectGoods" resultMap="goodsResultMap">
        SELECT * FROM goods
    </select>
    <select id="selectGoodsType" resultType="GoodType">
        SELECT * FROM data_dictionary WHERE type_code="good_type" AND value_id=#{value}
    </select>

@Test
    public void selectGoodsById() throws Exception {
        GoodsMapper mapper = sqlSession.getMapper(GoodsMapper.class);
        Goods goods = mapper.selectGoodsById();
        System.out.println(goods);
    }

    @Test
    public void selectGoods() throws Exception {
        GoodsMapper mapper = sqlSession.getMapper(GoodsMapper.class);
        GoodType goodType = mapper.selectGoodsType(3);
        System.out.println(goodType);
        List<Goods> list = mapper.selectGoods();
        for (Goods goods:list) {
            System.out.println(goods);
        }
    }

public interface GoodsMapper {
    Goods selectGoodsById();
    int insertGoods(Goods goods);
    List<Goods> selectGoods();
    GoodType selectGoodsType(int value);
}

注意

Mapped Statements collection does not contain value for com.study.mapper.GoodsMapper.selectGoodType ，遇到类似的错误提示就去xml文件中检查id是否一致（建议最好复制粘贴）