[Java知识库] MyBatis注解开发

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[Java知识库]MyBatis注解开发

MyBatis的常用注解

MyBatis也可使用注解开发方式，这样就可以减少编写Mappper映射文件

注解	说明
@Insert	实现新增
@Update	实现更新
@Delete	实现删除
@Select	实现查询
@Result	实现结果集封装
@Results	可以与@Result一起使用，封装多个结果集
@One	实现一对一结果集封装
@Many	实现一对多结果集封装

使用XML方式

UserMapper.xml

<?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.zg.mapper.UserMapper" >

    <insert id="save" parameterType="user" >
        insert into user values (#{id},#{username},#{password},#{birthday})
    </insert>

    <update id="update" parameterType="user">
        update user set username=#{username},password=#{password} where id=#{id}
    </update>

    <delete id="delete" parameterType="int">
        delete  from user where id=#{id}
    </delete>

    <select id="findById" parameterType="int" resultType="user">
        select * from  user where id=#{id}
    </select>

    <select id="findAll" resultType="user">
        select * from user
    </select>
</mapper>

UserMapper

package com.zg.mapper;

import com.zg.domain.User;

import java.util.List;

public interface UserMapper {
    public void save(User user);

    public void update(User user);

    public void delete(int id);

    public User findById(int id);

    public List<User> findAll();
}

测试

package com.zg.test;

import com.zg.domain.User;
import com.zg.mapper.UserMapper;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

public class MyBatisTest {

    private UserMapper mapper;

    @Before
    public void before() throws IOException {
        InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession = sessionFactory.openSession(true);
        mapper = sqlSession.getMapper(UserMapper.class);
    }
    @Test
    public void testSave(){
        User user = new User();
        user.setId(7);
        user.setUsername("Bob");
        user.setPassword("123");
        mapper.save(user);

    }

    @Test
    public void testUpdate(){
        User user = new User();
        user.setId(7);
        user.setUsername("Alice");
        user.setPassword("123");
        mapper.update(user);
    }

    @Test
    public void testDelete(){
        User user = new User();

        mapper.delete(7);
    }

    @Test
    public void testFindById(){
        User byId = mapper.findById(2);
        System.out.println(byId);
    }

    @Test
    public void testFindAll(){
        List<User> all = mapper.findAll();
        for (User user : all) {
            System.out.println(user);
        }
    }




}

MyBatis的增删改查

当我们将UserMapper.xml文件删除后，在sqlMapConfig.xml中配置查询语句的映射文件UserMapper.xml就没有了，但是映射关系还依然在，此时在sqlMapConfig.xml中就不用加载映射文件而是加载映射关系，然后将注解写在接口中就好

UserMapper接口

package com.zg.mapper;

import com.zg.domain.User;
import org.apache.ibatis.annotations.Delete;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.annotations.Update;

import java.util.List;

public interface UserMapper {
    @Insert("insert into user values (#{id},#{username},#{password},#{birthday})")
    public void save(User user);

    @Update(" update user set username=#{username},password=#{password} where id=#{id}")
    public void update(User user);

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

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

    @Select(" select * from user")
    public List<User> findAll();
}

核心配置文件sqlMapConfig.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd">
<!--主要配置mybatis的核心配置-->
<configuration>
    <!--通过properties标签加载外部properties文件-->
    <properties resource="jdbc.properties"></properties>
    <!--自定义别名-->
    <typeAliases>
        <typeAlias type="com.zg.domain.User" alias="user"></typeAlias>
    </typeAliases>

    <!--配置当前数据源的环境-->
    <environments default="developement">
        <environment id="developement">
            <transactionManager type="JDBC"></transactionManager>
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driver}"/>
                <property name="url" value="${jdbc.url}"/>
                <property name="username" value="${jdbc.username}"/>
                <property name="password" value="${jdbc.password}"/>
            </dataSource>
        </environment>
    </environments>
    <!--加载映射关系-->
    <mappers>
        <!--指定接口所在的包-->
        <package name="com.zg.mapper"/>
    </mappers>
</configuration>

测试代码依然同xml开发的代码

MyBatis的注解实现复杂映射开发

实现复杂关系映射之前我们可以在映射文件中通过配置<resultMap>来实现，我们可以使用@Results注解，@result注解，@One注解，@Many注解组合完成复杂关系的配置

注解	用法
`@Results`	代替的是标签`<resultMap>`该注解中可以使用单个@Result注解，也可以使用@Result集合，使用格式：`@Results（{@Results(),@Result()}）或@Results(@Result())`
`@Result`	代替了`<id>`标签和`<result>`标签`@Result`中属性介绍：[column:数据库的列名；property：需要装配的属性名；one：需要使用的`@One`注解（`@Result（one=@One）()`）;many:需要使用的@Many注解(`@Result(many=@many)()`)]
`@One`(一对一)	代替了`<assocation>`标签，是多表查询的关键，在注解中用来指定子查询返回单一对象。`@One`注解属性介绍：[select：指定用来多表查询的sqlmapper,使用格式：`@Result(column=" " ,property="",one=@One(select=")) ]`
`@Many`（多对一）	代替了`<collection>`标签，是多表查询的关键，在注解中用来指定子查询返回对象集合。使用格式：`@Result(property="",column="",many=@Many(select=""))`

一对一查询

用户表和订单表的关系为，一个用户多个订单，一个订单只从属一个用户
一对一查询的需求：查询一个订单，与此同时查询出该订单所属的用户
在这里插入图片描述
在只查询order表的时候，也要查询user表，所以需要将所有数据全部查出进行封装SELECT *,o.id oid FROM orders o,USER u WHERE o.uid=u.id在封装时order中有user，但是user中的数据无法封装到order中，只能进行人工封装

创建Order和User实体

在这里插入图片描述

创建OrderMapper接口

package com.zg.mapper;


import com.zg.domain.Order;
import com.zg.domain.User;
import org.apache.ibatis.annotations.One;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;

import java.util.List;

public interface OrderMapper {


    @Select("select *,o.id oid from orders o,user u where o.uid=u.id")
    @Results({
            @Result(column = "oid",property = "id"),
            @Result(column = "ordertime",property = "ordertime"),
            @Result(column = "total",property = "total"),
            @Result(column = "uid",property = "user.id"),
            @Result(column = "username",property = "user.username"),
            @Result(column = "password",property = "user.password")
    })
    public List<Order> findAll();

}

测试

package com.zg.test;

import com.zg.domain.Order;
import com.zg.domain.User;
import com.zg.mapper.OrderMapper;
import com.zg.mapper.UserMapper;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

public class MyBatisTest1 {

    private OrderMapper mapper;

    @Before
    public void before() throws IOException {
        InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession = sessionFactory.openSession(true);
        mapper = sqlSession.getMapper(OrderMapper.class);
    }

    @Test
    public void test1(){
        List<Order> all = mapper.findAll();
        for (Order order : all) {
            System.out.println(order);
        }
    }



}

运行结果

在这里插入图片描述

通过外键查询另外一张表

uid属于order的外键，所以通过uid进行查询user表中的数据，但是在UserMapper中我们已经写过了findById方法，所以这里可直接使用一对一查询注解语法通过select -->UserMapper的全限定名即可

package com.zg.mapper;


import com.zg.domain.Order;
import com.zg.domain.User;
import org.apache.ibatis.annotations.One;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;

import java.util.List;

public interface OrderMapper {


    @Select("select *from orders")
    @Results({
            @Result(column = "id",property = "id"),
            @Result(column = "ordertime",property = "ordertime"),
            @Result(column = "total",property = "total"),
            @Result(
                    property = "user",//要封装的属性名称是谁
                    column = "uid",//根据哪个字段进行查询user表数据，即外键
                    javaType = User.class,//要封装的实体类型
                    //one = @One一对一查询注解语法
                    //select，属性，代表查询哪个接口（UserMapper）的方法findById（）获得数据
                    one = @One(select = "com.zg.mapper.UserMapper.findById")
            )
    })
    public List<Order> findAll();
}

在这里插入图片描述

一对多查询

用户表和订单表的关系为，一个用户有多个订单，一个当但只从属一个用户
一对多查询需求：查询一个用户，与此同时查询出该用户具有的订单
在这里插入图片描述

select *,o.id oid from user u,orders o where u.id=o.uid

在这里插入图片描述

修改User实体

在这里插入图片描述

编写UserMapper接口

package com.zg.mapper;

import com.zg.domain.User;
import org.apache.ibatis.annotations.*;

import java.util.List;

public interface UserMapper {
    @Insert("insert into user values (#{id},#{username},#{password},#{birthday})")
    public void save(User user);

    @Update(" update user set username=#{username},password=#{password} where id=#{id}")
    public void update(User user);

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

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

    @Select(" select * from user")
    public List<User> findAll();

    @Select(" select * from user")
    @Results({
            //id=true表示这是一个为主键的id
            @Result(id = true ,column = "id",property = "id"),
            @Result(column = "username",property = "username"),
            @Result(column = "password",property = "password"),
            @Result(
                    property = "orderList",
                    column = "id",//取user中查询出的id当作对方查询出的uid
                    javaType = List.class,
                    many = @Many(select = "com.zg.mapper.OrderMapper.findByUid")
            )
    })
    public List<User> findUserAndOrderAll();
}

测试代码

package com.zg.test;

import com.zg.domain.Order;
import com.zg.domain.User;
import com.zg.mapper.OrderMapper;
import com.zg.mapper.UserMapper;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

public class MyBatisTest2 {

    private UserMapper mapper;

    @Before
    public void before() throws IOException {
        InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
        SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession = sessionFactory.openSession(true);
        mapper = sqlSession.getMapper(UserMapper.class);
    }

    @Test
    public void test1(){
        List<User> userAndOrderAll = mapper.findUserAndOrderAll();
        for (User user : userAndOrderAll) {
            System.out.println(user);
        }
    }



}

在这里插入图片描述

测试结果

在这里插入图片描述

多对多查询

用户表和角色表的关系为，一个用户有多个角色，一个角色被多个用户使用
多对多查询的需求：查询用户同时查询该用户的所有角色
在这里插入图片描述

select * from user u,sys_user_role ur ,sys_role r where u.id=ur.userId and ur.roleId=r.id

在这里插入图片描述

创建Role实体，修改User实体

在这里插入图片描述

添加UserMapper接口

package com.zg.mapper;

import com.zg.domain.User;
import org.apache.ibatis.annotations.*;

import java.util.List;

public interface UserMapper {
    @Insert("insert into user values (#{id},#{username},#{password},#{birthday})")
    public void save(User user);

    @Update(" update user set username=#{username},password=#{password} where id=#{id}")
    public void update(User user);

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

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

    @Select(" select * from user")
    public List<User> findAll();

    @Select(" select * from user")
    @Results({
            //id=true表示这是一个为主键的id
            @Result(id = true ,column = "id",property = "id"),
            @Result(column = "username",property = "username"),
            @Result(column = "password",property = "password"),
            @Result(
                    property = "orderList",
                    column = "id",//取user中查询出的id当作对方查询出的uid
                    javaType = List.class,
                    many = @Many(select = "com.zg.mapper.OrderMapper.findByUid")
            )
    })
    public List<User> findUserAndOrderAll();


    @Select("SELECT * FROM USER")
    @Results({
            @Result(id = true,column = "id",property = "id"),
            @Result(column = "username",property = "username"),
            @Result(column = "password",property = "password"),
            @Result(
                    property = "roleList",
                    column = "id",
                    javaType = List.class,
                    many = @Many(select = "com.zg.mapper.RoleMapper.findByUid")
            )
    })
    public List<User> findUserAndRoleAll();
}

RoleMapper接口

package com.zg.mapper;


import com.zg.domain.Role;
import org.apache.ibatis.annotations.Select;

import java.util.List;

public interface RoleMapper {

    @Select("SELECT * FROM sys_user_role ur,sys_role r WHERE ur.roleId=r.id AND ur.userId=#{uid}")
    public List<Role> findByUid(int uid);

}