Mybatis基于注解实现多表查询

　　对应的四种数据库表关系中存在四种关系：一对多，多对应，一对一，多对多。在前文中已经实现了xml配置方式实现表关系的查询，本文记录一下Mybatis怎么通过注解实现多表的查询，算是一个知识的补充。

　　同样的先介绍一下Demo的情况:存在两个实体类用户类和账户类，用户类可能存在多个账户，即一对多的表关系。每个账户只能属于一个用户，即一对一或者多对一关系。我们最后实现两个方法，第一个实现查询所有用户信息并同时查询出每个用户的账户信息，第二个实现查询所有的账户信息并且同时查询出其所属的用户信息。

　　1.项目结构

　　2.领域类

public class Account implements Serializable{
    private Integer id;
    private Integer uid;
    private double money;
    private User user; //加入所属用户的属性
    省略get 和set 方法.............................        
}
public class User implements Serializable{

private Integer userId;

private String userName;

private Date userBirthday;

private String userSex;

private String userAddress;

private List<Account> accounts;

省略get 和set 方法.............................

}

　　在User中因为一个用户有多个账户所以添加Account的列表，在Account中因为一个账户只能属于一个User,所以添加User的对象。　

　　3.Dao层

 1 public interface AccountDao {
 2     /**
 3      *查询所有账户并同时查询出所属账户信息
 4      */
 5     @Select("select * from account")
 6     @Results(id = "accountMap",value = {
 7             @Result(id = true,property = "id",column = "id"),
 8             @Result(property = "uid",column = "uid"),
 9             @Result(property = "money",column = "money"),
10             //配置用户查询的方式 column代表的传入的字段，一对一查询用one select 代表使用的方法的全限定名， fetchType表示查询的方式为立即加载还是懒加载
11             @Result(property = "user",column = "uid",one = @One(select = "com.example.dao.UserDao.findById",fetchType = FetchType.EAGER))
12     })
13     List<Account> findAll();
14 
15     /**
16      * 根据用户ID查询所有账户
17      * @param id
18      * @return
19      */
20     @Select("select * from account where uid = #{id}")
21     List<Account> findAccountByUid(Integer id);
22 }
23 
24 
25 
26 public interface UserDao {
27     /**
28      * 查找所有用户
29      * @return
30      */
31     @Select("select * from User")
32     @Results(id = "userMap",value = {@Result(id = true,column = "id",property = "userId"),
33             @Result(column = "username",property = "userName"),
34             @Result(column = "birthday",property = "userBirthday"),
35             @Result(column = "sex",property = "userSex"),
36             @Result(column = "address",property = "userAddress"),
37             @Result(column = "id",property = "accounts",many = @Many(select = "com.example.dao.AccountDao.findAccountByUid",fetchType = FetchType.LAZY))
38     })
39     List<User> findAll();
40 
41     /**
42      * 保存用户
43      * @param user
44      */
45     @Insert("insert into user(username,birthday,sex,address) values(#{username},#{birthday},#{sex},#{address})")
46     void saveUser(User user);
47 
48     /**
49      * 更新用户
50      * @param user
51      */
52     @Update("update user set username=#{username},birthday=#{birthday},sex=#{sex},address=#{address} where id=#{id}")
53     void updateUser(User user);
54 
55     /**
56      * 删除用户
57      * @param id
58      */
59     @Delete("delete from user where id=#{id}")
60     void  deleteUser(Integer id);
61 
62     /**
63      * 查询用户根据ID
64      * @param id
65      * @return
66      */
67     @Select("select * from user where id=#{id}")
68     @ResultMap(value = {"userMap"})
69     User findById(Integer id);
70 
71     /**
72      * 根据用户名称查询用户
73      * @param name
74      * @return
75      */
76 //    @Select("select * from user where username like #{name}")
77     @Select("select * from user where username like '%${value}%'")
78     List<User> findByUserName(String name);
79 
80     /**
81      * 查询用户数量
82      * @return
83      */
84     @Select("select count(*) from user")
85     int findTotalUser();

View Code

　　在findAll()方法中配置@Results的返回值的注解，在@Results注解中使用@Result配置根据用户和账户的关系而添加的属性，User中的属性List<Account>一个用户有多个账户的关系的映射配置：@Result(column = "id",property = "accounts",many = @Many(select = "com.example.dao.AccountDao.findAccountByUid",fetchType = FetchType.LAZY))，使用@Many来向Mybatis表明其一对多的关系，@Many中的select属性对应的AccountDao中的findAccountByUid方法的全限定名，fetchType代表使用立即加载或者延迟加载，因为这里为一对多根据前面的讲解，懒加载的使用方式介绍一对多关系一般使用延迟加载，所以这里配置为LAZY方式。在Account中存在多对一或者一对一关系，所以配置返回值属性时使用：@Result(property = "user",column = "uid",one = @One(select = "com.example.dao.UserDao.findById",fetchType = FetchType.EAGER))，property代表领域类中声明的属性，column代表传入后面select语句中的参数，因为这里为一对一或者说为多对一，所以使用@One注解来描述其关系，EAGER表示使用立即加载的方式，select代表查询本条数据时所用的方法的全限定名，fetchType代表使用立即加载还是延迟加载。

　　4.Demo中Mybatis的配置

<?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">
<configuration>
    <settings>
        <!--&lt;!&ndash;开启全局的懒加载&ndash;&gt;-->
        <!--<setting name="lazyLoadingEnabled" value="true"/>-->
        <!--&lt;!&ndash;关闭立即加载，其实不用配置，默认为false&ndash;&gt;-->
        <!--<setting name="aggressiveLazyLoading" value="false"/>-->
        <!--开启Mybatis的sql执行相关信息打印-->
        <setting name="logImpl" value="STDOUT_LOGGING" />
        <!--<setting name="cacheEnabled" value="true"/>-->
    </settings>
    <typeAliases>
        <typeAlias type="com.example.domain.User" alias="user"/>
        <package name="com.example.domain"/>
    </typeAliases>
    <environments default="test">
        <environment id="test">
            <!--配置事务-->
            <transactionManager type="jdbc"></transactionManager>
            <!--配置连接池-->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/test1"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <package name="com.example.dao"/>
    </mappers>
</configuration>

　　主要是记得开启mybatis中sql执行情况的打印，方便我们查看执行情况。

　　5.测试

　　（1）测试查询用户同时查询出其账户的信息

　　　测试代码：

public class UserTest {
</span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> InputStream in;
</span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> SqlSessionFactory sqlSessionFactory;
</span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> SqlSession sqlSession;
</span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> UserDao userDao;
@Before
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span> init()<span style="color: rgba(0, 0, 255, 1)">throws</span><span style="color: rgba(0, 0, 0, 1)"> Exception{
    in </span>= Resources.getResourceAsStream("SqlMapConfig.xml"<span style="color: rgba(0, 0, 0, 1)">);
    sqlSessionFactory </span>= <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> SqlSessionFactoryBuilder().build(in);
    sqlSession </span>=<span style="color: rgba(0, 0, 0, 1)"> sqlSessionFactory.openSession();
    userDao </span>= sqlSession.getMapper(UserDao.<span style="color: rgba(0, 0, 255, 1)">class</span><span style="color: rgba(0, 0, 0, 1)">);
}
@After
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span> destory()<span style="color: rgba(0, 0, 255, 1)">throws</span><span style="color: rgba(0, 0, 0, 1)"> Exception{
    sqlSession.commit();
    sqlSession.close();
    in.close();
}
@Test
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> testFindAll(){
    List</span>&lt;User&gt; userList =<span style="color: rgba(0, 0, 0, 1)"> userDao.findAll();
    </span><span style="color: rgba(0, 0, 255, 1)">for</span><span style="color: rgba(0, 0, 0, 1)"> (User user: userList){
        System.out.println(</span>"每个用户信息"<span style="color: rgba(0, 0, 0, 1)">);
        System.out.println(user);
        System.out.println(user.getAccounts());
    }
}</span></pre>

　　测试结果：

（2）查询所有账户信息同时查询出其所属的用户信息

　　测试代码：

public class AccountTest {
</span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> InputStream in;
</span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> SqlSessionFactory sqlSessionFactory;
</span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> SqlSession sqlSession;
</span><span style="color: rgba(0, 0, 255, 1)">private</span><span style="color: rgba(0, 0, 0, 1)"> AccountDao accountDao;
@Before
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span> init()<span style="color: rgba(0, 0, 255, 1)">throws</span><span style="color: rgba(0, 0, 0, 1)"> Exception{
    in </span>= Resources.getResourceAsStream("SqlMapConfig.xml"<span style="color: rgba(0, 0, 0, 1)">);
    sqlSessionFactory </span>= <span style="color: rgba(0, 0, 255, 1)">new</span><span style="color: rgba(0, 0, 0, 1)"> SqlSessionFactoryBuilder().build(in);
    sqlSession </span>=<span style="color: rgba(0, 0, 0, 1)"> sqlSessionFactory.openSession();
    accountDao </span>= sqlSession.getMapper(AccountDao.<span style="color: rgba(0, 0, 255, 1)">class</span><span style="color: rgba(0, 0, 0, 1)">);
}
@After
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span> destory()<span style="color: rgba(0, 0, 255, 1)">throws</span><span style="color: rgba(0, 0, 0, 1)"> Exception{
    sqlSession.commit();
    sqlSession.close();
    in.close();
}
@Test
</span><span style="color: rgba(0, 0, 255, 1)">public</span> <span style="color: rgba(0, 0, 255, 1)">void</span><span style="color: rgba(0, 0, 0, 1)"> testFindAll(){
    List</span>&lt;Account&gt; accountList =<span style="color: rgba(0, 0, 0, 1)"> accountDao.findAll();
    </span><span style="color: rgba(0, 0, 255, 1)">for</span><span style="color: rgba(0, 0, 0, 1)"> (Account account: accountList){
        System.out.println(</span>"查询的每个账户"<span style="color: rgba(0, 0, 0, 1)">);
        System.out.println(account);
        System.out.println(account.getUser());
    }
}

}