mybatis的通用mapper，多用於單表查詢，接口內部爲我們提供了單表查詢的基礎查詢語法，可以極大地幫助我們簡化編程。
接下來讓我們動手試一試：
我建的是springboot項目：
先導依賴：
<dependency>
<groupId>tk.mybatis</groupId>
<artifactId>mapper-spring-boot-starter</artifactId>
<version>2.0.4</version>
</dependency>
這裏連接池我用的是阿里的druid,數據庫用的mysql
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>druid</artifactId>
<version>1.1.12</version>
</dependency>
我的數據庫兩張測試用表：
接下來搭建基本框架，先寫實體類:
需要注意的是：使用通用Mapper需要給實體類加註解：
@Entity
@Table(name="t_users")
public class User implements Serializable{
private static final long serialVersionUID = 8941012353272388061L;
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private Long id;
@Column
private String name;
@Column
private String password;
@Column(name="role_id")
private Long roleId;
}
別忘了實體類的getter/setter方法，然後dao層實現Mapper接口，注意UserMapper是接口不是類
public interface UserMapper extends Mapper<User> {
}
然後在主類上打開mapper掃描，
注意是tk.mybatis下的@MapperScan, 不要導成org.mybatis.spring.annotation.MapperScan
import tk.mybatis.spring.annotation.MapperScan;
@SpringBootApplication
@MapperScan("com.test.dao")
public class MapperTestApplication {
public static void main(String[] args) {
SpringApplication.run(MapperTestApplication.class, args);
}
}
準備就緒，接下來測試；
1)、（單條件查詢）根據role_id查詢所有人
業務類：
/*
* 根據role_id查詢所有人
* select * from t_users where role_id = ？;
*/
@Override
public List<User> selectByUser1(User user) {
Example example = new Example(User.class,true,true);
Example.Criteria ec = example.createCriteria();
ec.andEqualTo("roleId", user.getRoleId());
return userMapper.selectByExample(example);
}
測試類：
@RunWith(SpringRunner.class)
@SpringBootTest
public class MapperTestApplicationTests {
@Autowired
private IUserServ userServ;
@Test
public void contextLoads() {
User user = new User();
user.setRoleId(1L);
List<User> ulist = userServ.selectByUser1(user);
ulist.forEach(System.err::println);
}
}
測試結果：通過：控制檯打印
DEBUG 6268 --- [main] com.test.dao.UserMapper.selectByExample : ==> Preparing: SELECT id,name,password,role_id FROM t_users WHERE ( role_id = ? )
DEBUG 6268 --- [main] com.test.dao.UserMapper.selectByExample : ==> Parameters: 1(Long)
DEBUG 6268 --- [main] com.test.dao.UserMapper.selectByExample : <== Total: 4
User [id=2, name=員工1, password=111, roleId=1, role=Role [id=null, describe=null]]
User [id=3, name=員工2, password=222, roleId=1, role=Role [id=null, describe=null]]
User [id=4, name=員工3, password=333, roleId=1, role=Role [id=null, describe=null]]
User [id=5, name=員工4, password=444, roleId=1, role=Role [id=null, describe=null]]
2）測試二：（多條件查詢）
業務類：
/*
（多條件查詢）根據role_id查詢id大於min小於max，或者name爲？的人
* select * from t_users where role_id = ？ and id between min and max and name = ?
*/
@Override
public List<User> selectByUser2(Long min,Long max,User user) {
Example example = new Example(User.class,true,true);
Example.Criteria ec = example.createCriteria();
ec.andEqualTo("roleId", user.getRoleId()).andBetween("id", min, max).orEqualTo("name", user.getName());
return userMapper.selectByExample(example);
}
測試類：
@Test
public void contextLoads() {
User user = new User();
user.setRoleId(1L);
user.setName("員工4");
List<User> ulist = userServ.selectByUser2(2L,3L,user);
ulist.forEach(System.err::println);
}
測試結果：通過。控制檯打印：
DEBUG 14728 --- [main] com.test.dao.UserMapper.selectByExample : ==> Preparing: SELECT id,name,password,role_id FROM t_users WHERE ( role_id = ? and id between ? and ? or name = ? )
DEBUG 14728 --- [main] com.test.dao.UserMapper.selectByExample : ==> Parameters: 1(Long), 2(Long), 3(Long), 員工4(String)
DEBUG 14728 --- [main] com.test.dao.UserMapper.selectByExample : <== Total: 3
User [id=2, name=員工1, password=111, roleId=1, role=Role [id=null, describe=null]]
User [id=3, name=員工2, password=222, roleId=1, role=Role [id=null, describe=null]]
User [id=5, name=員工4, password=444, roleId=1, role=Role [id=null, describe=null]]
3）排序（我們繼續用剛纔的多條件查詢，結果倒序）
select * from t_users where ( role_id = ? and id between ? and ? or name = ? ) order by id DESC
業務層：（加example.setOrderByClause("id DESC");）
@Override
public List<User> selectByUser2(Long min,Long max,User user) {
Example example = new Example(User.class,true,true);
Example.Criteria ec = example.createCriteria();
ec.andEqualTo("roleId", user.getRoleId()).andBetween("id", min, max).orEqualTo("name", user.getName());
example.setOrderByClause("id DESC");
return userMapper.selectByExample(example);
}
測試類不變：
測試結果：通過：控制檯打印
DEBUG 10780 --- [main] com.test.dao.UserMapper.selectByExample : ==> Preparing: SELECT id,name,password,role_id FROM t_users WHERE ( role_id = ? and id between ? and ? or name = ? ) order by id DESC
DEBUG 10780 --- [main] com.test.dao.UserMapper.selectByExample : ==> Parameters: 1(Long), 2(Long), 3(Long), 員工4(String)
DEBUG 10780 --- [main] com.test.dao.UserMapper.selectByExample : <== Total: 3
User [id=5, name=員工4, password=444, roleId=1, role=Role [id=null, describe=null]]
User [id=3, name=員工2, password=222, roleId=1, role=Role [id=null, describe=null]]
User [id=2, name=員工1, password=111, roleId=1, role=Role [id=null, describe=null]]
此外：Example類還爲我們封裝了指定列查詢，排除列查詢等許多單表查詢的方法，具體需求具體分析，我們可以去追 Example類的源碼找尋自己需要的方法。
總結：通用Mapper適合於基於單表的複雜查詢，涉及多張表的查詢建議使用反向映射生成mapper.XML查詢