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();
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> <!--<!–开启全局的懒加载–>--> <!--<setting name="lazyLoadingEnabled" value="true"/>--> <!--<!–关闭立即加载，其实不用配置，默认为false–>--> <!--<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><User> 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><Account> 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()); } }}
测试结果：
