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MyBatis多表查询

MyBatis的多表查询只需要DAO接口和sql语句即可，主要的是mapper里的返回字段要正确

现在有4张表

SELECT * FROM mybatis.user;
select * from mybatis.role;
select * from mybatis.account;
select * from mybatis.user_role;

user

role

account

user_role

工程结构

DAO层

import com.jinke.domain.Account;

import java.util.List;

public interface AccountDao {

    List<Account> findAll();
}

import com.jinke.domain.Role;

import java.util.List;

public interface RoleDao {

    List<Role> findAll();
}

import com.jinke.domain.User;

import java.util.List;

public interface UserDao {
    List<User> findAll();
}

实体类

import java.io.Serializable;

public class Account implements Serializable {

    private Integer id;
    private Integer uid;
    private Double money;

    private User user;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public Integer getUid() {
        return uid;
    }

    public void setUid(Integer uid) {
        this.uid = uid;
    }

    public Double getMoney() {
        return money;
    }

    public void setMoney(Double money) {
        this.money = money;
    }

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }

    @Override
    public String toString() {
        return "Account{" +
                "id=" + id +
                ", uid=" + uid +
                ", money=" + money +
                '}';
    }
}

import java.io.Serializable;
import java.util.List;

public class Role implements Serializable {
    private Integer id;
    private String rolename;
    private String roledesc;

    private List<User> users;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getRolename() {
        return rolename;
    }

    public void setRolename(String rolename) {
        this.rolename = rolename;
    }

    public String getRoledesc() {
        return roledesc;
    }

    public void setRoledesc(String roledesc) {
        this.roledesc = roledesc;
    }

    public List<User> getUsers() {
        return users;
    }

    public void setUsers(List<User> users) {
        this.users = users;
    }

    @Override
    public String toString() {
        return "Role{" +
                "id=" + id +
                ", rolename='" + rolename + '\'' +
                ", roledesc='" + roledesc + '\'' +
                '}';
    }
}

import java.io.Serializable;
import java.util.Date;
import java.util.List;

public class User implements Serializable {
    private Integer id;
    private String username;
    private String address;
    private String sex;
    private Date birthday;

    private List<Role> roles;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public List<Role> getRoles() {
        return roles;
    }

    public void setRoles(List<Role> roles) {
        this.roles = roles;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", address='" + address + '\'' +
                ", sex='" + sex + '\'' +
                ", birthday=" + birthday +
                '}';
    }
}

sql配置文件

AccountDao.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.jinke.dao.AccountDao">

    <resultMap id="accountUserMap" type="account">
        <id property="id" column="aid"/>
        <result property="uid" column="uid"/>
        <result property="money" column="money"/>
        <!--一对一的关系映射，配置封装user的内容-->
        <association property="user" column="uid" javaType="user">
            <id property="id" column="id"/>
            <result column="username" property="username"/>
            <result column="address" property="address"/>
            <result column="sex" property="sex"/>
            <result column="birthday" property="birthday"/>
        </association>
    </resultMap>

    <select id="findAll" resultMap="accountUserMap">
        select * from user a,account b where a.id = b.uid
    </select>
</mapper>

RoleDao.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.jinke.dao.RoleDao">

    <resultMap id="roleMap" type="role">
        <id property="id" column="rid"/>
        <result property="rolename" column="rolename"/>
        <result property="roledesc" column="roledesc"/>
        <collection property="users" ofType="user">
            <id property="id" column="id"/>
            <result property="username" column="username"/>
            <result property="sex" column="sex"/>
            <result property="address" column="address"/>
            <result property="birthday" column="birthday"/>
        </collection>
    </resultMap>

    <select id="findAll" resultMap="roleMap">
        select u.*,r.id as rid,r.rolename,r.roledesc from mybatis.role as r
        left outer join mybatis.user_role as ur on r.id = ur.rid
        left outer join mybatis.user as u on u.id = ur.uid
    </select>
</mapper>

UserDao.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.jinke.dao.UserDao">

    <resultMap id="userAccountMap" type="user">
        <id property="id" column="id"/>
        <result property="username" column="username"/>
        <result property="address" column="address"/>
        <result property="sex" column="sex"/>
        <result property="birthday" column="birthday"/>
        <collection property="roles" ofType="role">
            <id property="id" column="rid"/>
            <result property="rolename" column="rolename"/>
            <result property="roledesc" column="roledesc"/>
        </collection>
    </resultMap>

    <select id="findAll" resultMap="userAccountMap">
        select u.*,r.id as rid,r.rolename,r.roledesc from mybatis.user as u
        left outer join mybatis.user_role as ur on u.id = ur.uid
        left outer join mybatis.role as r on r.id = ur.rid
    </select>

    <select id="findById" parameterType="Integer" resultType="user">
        select * from user where id = #{uid};
    </select>
</mapper>

测试类

import com.jinke.dao.AccountDao;
import com.jinke.dao.RoleDao;
import com.jinke.dao.UserDao;
import com.jinke.domain.Account;
import com.jinke.domain.Role;
import com.jinke.domain.User;
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.After;
import org.junit.Before;
import org.junit.Test;

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

public class MyBatisTest {

    private InputStream in;
    private SqlSession sqlSession;
    private UserDao userDao;
    private AccountDao accountDao;
    private RoleDao roleDao;

    @Before
    public void init() throws Exception {
        in = Resources.getResourceAsStream("SqlMapConfig.xml");
        SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
        SqlSessionFactory factory = builder.build(in);
        sqlSession = factory.openSession();
        userDao = sqlSession.getMapper(UserDao.class);
        accountDao = sqlSession.getMapper(AccountDao.class);
        roleDao = sqlSession.getMapper(RoleDao.class);
    }

    @After
    public void destroy() throws Exception {
        sqlSession.commit();
        sqlSession.close();
        in.close();
    }

    @Test
    public void testFindAccount() {
        List<Account> accounts = accountDao.findAll();
        for (Account account : accounts) {
            System.out.println(account + " " + account.getUser());
        }
    }

    @Test
    public void testFindUser() {
        List<User> users = userDao.findAll();
        for (User user : users) {
            System.out.println(user + " " + user.getRoles());
        }
    }

    @Test
    public void testFindRole() {
        List<Role> roles = roleDao.findAll();
        for (Role role : roles) {
            System.out.println(role + " " + role.getUsers());
        }
    }
}