MyBatis多表查詢和注解開發(fā)案例詳解
Mybatis多表查詢
一對一查詢
一對一查詢的模型
用戶表和訂單表的關(guān)系為，一個用戶有多個訂單，一個訂單只從屬于一個用戶
一對一查詢的需求：查詢一個訂單，與此同時查詢出該訂單所屬的用戶
一對一查詢的語句
對應(yīng)的sql語句：
SELECT *,o.id oid FROM orders o,USER u WHERE o.uid=u.id;
查詢的結(jié)果如下：
創(chuàng)建Order和User實(shí)體
public class Order {
private int id;
private Date ordertime;
private double total;
//代表當(dāng)前訂單從屬于哪一個客戶
private User user;
}
public class User {
private int id;
private String username;
private String password;
private Date birthday;
}創(chuàng)建OrderMapper接口
public interface OrderMapper {
List<Order> findAll();
}配置OrderMapper.xml
<mapper namespace="com.zjq.mapper.OrderMapper">
<resultMap id="orderMap" type="com.zjq.domain.Order">
<result column="uid" property="user.id"></result>
<result column="username" property="user.username"></result>
<result column="password" property="user.password"></result>
<result column="birthday" property="user.birthday"></result>
</resultMap>
<select id="findAll" resultMap="orderMap">
SELECT *,o.id oid FROM orders o,USER u WHERE o.uid=u.id
</select>
</mapper>其中還可以配置如下：
<resultMap id="orderMap" type="com.zjq.domain.Order">
<result property="id" column="id"></result>
<result property="ordertime" column="ordertime"></result>
<result property="total" column="total"></result>
<association property="user" javaType="com.zjq.domain.User">
<result column="uid" property="id"></result>
<result column="username" property="username"></result>
<result column="password" property="password"></result>
<result column="birthday" property="birthday"></result>
</association>
</resultMap>
<resultMap id="orderMap" type="com.zjq.domain.Order">
<result property="id" column="id"></result>
<result property="ordertime" column="ordertime"></result>
<result property="total" column="total"></result>
<association property="user" javaType="com.zjq.domain.User">
<result column="uid" property="id"></result>
<result column="username" property="username"></result>
<result column="password" property="password"></result>
<result column="birthday" property="birthday"></result>
</association>
</resultMap>測試結(jié)果
OrderMapper mapper = sqlSession.getMapper(OrderMapper.class);
List<Order> all = mapper.findAll();
for(Order order : all){
System.out.println(order);
}
輸出：
一對多查詢
一對多查詢的模型
用戶表和訂單表的關(guān)系為，一個用戶有多個訂單，一個訂單只從屬于一個用戶
一對多查詢的需求：查詢一個用戶，與此同時查詢出該用戶具有的訂單
一對多查詢的語句
對應(yīng)的sql語句：
select *,o.id oid from user u left join orders o on u.id=o.uid;
查詢的結(jié)果如下：
修改User實(shí)體
public class Order {
private int id;
private Date ordertime;
private double total;
//代表當(dāng)前訂單從屬于哪一個客戶
private User user;
}
public class User {
private int id;
private String username;
private String password;
private Date birthday;
//代表當(dāng)前用戶具備哪些訂單
private List<Order> orderList;
}創(chuàng)建UserMapper接口
public interface UserMapper {
List<User> findAll();
}配置UserMapper.xml
<mapper namespace="com.zjq.mapper.UserMapper">
<resultMap id="userMap" type="com.zjq.domain.User">
<result column="id" property="id"></result>
<result column="username" property="username"></result>
<result column="password" property="password"></result>
<result column="birthday" property="birthday"></result>
<collection property="orderList" ofType="com.zjq.domain.Order">
<result column="oid" property="id"></result>
<result column="ordertime" property="ordertime"></result>
<result column="total" property="total"></result>
</collection>
</resultMap>
<select id="findAll" resultMap="userMap">
select *,o.id oid from user u left join orders o on u.id=o.uid
</select>
</mapper>測試結(jié)果
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
List<User> all = mapper.findAll();
for(User user : all){
System.out.println(user.getUsername());
List<Order> orderList = user.getOrderList();
for(Order order : orderList){
System.out.println(order);
}
System.out.println("----------------------------------");
}
輸出：
15:00:24,330 DEBUG findAll:159 - ==> Preparing: select u.id uid,u.username ,o.id oid,o.ordertime,o.total from user u left join orders o on u.id=o.uid
15:00:24,360 DEBUG findAll:159 - ==> Parameters:
15:00:24,393 DEBUG findAll:159 - <== Total: 5
User{id=1, username='admin', password='null', birthday=null, roleList=null, orderList=[Order{id=1, ordertime=Sun Apr 16 14:23:50 CST 2023, total=2000.0, user=null}]}
User{id=2, username='共飲一杯無666', password='null', birthday=null, roleList=null, orderList=[Order{id=2, ordertime=Sun Apr 16 14:23:50 CST 2023, total=8888.0, user=null}]}
User{id=3, username='共飲一杯無', password='null', birthday=null, roleList=null, orderList=[Order{id=3, ordertime=Sun Apr 16 14:23:50 CST 2023, total=3699.0, user=null}]}
User{id=4, username='共飲一杯無', password='null', birthday=null, roleList=null, orderList=[]}
User{id=5, username='共飲一杯無', password='null', birthday=null, roleList=null, orderList=[]}
多對多查詢
多對多查詢的模型
用戶表和角色表的關(guān)系為，一個用戶有多個角色，一個角色被多個用戶使用
多對多查詢的需求：查詢用戶同時查詢出該用戶的所有角色
多對多查詢的語句
對應(yīng)的sql語句：
select u.*,r.*,r.id rid from user u left join sys_user_role ur on u.id=ur.userid inner join sys_role r on ur.roleid=r.id;
查詢的結(jié)果如下：
創(chuàng)建Role實(shí)體，修改User實(shí)體
public class User {
private int id;
private String username;
private String password;
private Date birthday;
//代表當(dāng)前用戶具備哪些訂單
private List<Order> orderList;
//代表當(dāng)前用戶具備哪些角色
private List<Role> roleList;
}
public class Role {
private int id;
private String rolename;
}添加UserMapper接口方法
List<User> findAllUserAndRole();
配置UserMapper.xml
<resultMap id="userRoleMap" type="com.zjq.domain.User">
<result column="id" property="id"></result>
<result column="username" property="username"></result>
<result column="password" property="password"></result>
<result column="birthday" property="birthday"></result>
<collection property="roleList" ofType="com.zjq.domain.Role">
<result column="rid" property="id"></result>
<result column="rolename" property="rolename"></result>
</collection>
</resultMap>
<select id="findAllUserAndRole" resultMap="userRoleMap">
select u.*,r.*,r.id rid from user u left join sys_user_role ur on u.id=ur.userid
inner join sys_role r on ur.roleid=r.id;
</select>測試結(jié)果
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
List<User> all = mapper.findAllUserAndRole();
for(User user : all){
System.out.println(user.getUsername());
List<Role> roleList = user.getRoleList();
for(Role role : roleList){
System.out.println(role);
}
System.out.println("----------------------------------");
}
11:45:51,443 DEBUG findUserAndRoleAll:159 - ==> Preparing: SELECT * FROM USER u,sys_user_role ur,sys_role r WHERE u.id=ur.userId AND ur.roleId=r.id
11:45:51,572 DEBUG findUserAndRoleAll:159 - ==> Parameters:
User{id=1, username='zjq', password='abc', birthday=Wed Jul 28 00:00:00 GMT+08:00 2021, roleList=[Role{id=1, roleName='CTO', roleDesc='CTO'}, Role{id=2, roleName='COO', roleDesc='COO'}]}
User{id=2, username='jack', password='123456', birthday=Fri Aug 20 00:00:00 GMT+08:00 2021, roleList=[Role{id=1, roleName='CTO', roleDesc='CTO'}, Role{id=2, roleName='COO', roleDesc='COO'}]}
11:45:51,610 DEBUG findUserAndRoleAll:159 - <== Total: 4
11:45:51,618 DEBUG JdbcTransaction:123 - Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@6ec8211c]
11:45:51,619 DEBUG JdbcTransaction:91 - Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@6ec8211c]
11:45:51,619 DEBUG PooledDataSource:363 - Returned connection 1858609436 to pool.
Mybatis的注解開發(fā)
MyBatis的常用注解
這幾年來注解開發(fā)越來越流行，Mybatis也可以使用注解開發(fā)方式，這樣我們就可以減少編寫Mapper
映射文件了。我們先圍繞一些基本的CRUD來學(xué)習(xí)，再學(xué)習(xí)復(fù)雜映射多表操作。
@Insert：實(shí)現(xiàn)新增@Update：實(shí)現(xiàn)更新@Delete：實(shí)現(xiàn)刪除@Select：實(shí)現(xiàn)查詢@Result：實(shí)現(xiàn)結(jié)果集封裝@Results：可以與@Result 一起使用，封裝多個結(jié)果集@One：實(shí)現(xiàn)一對一結(jié)果集封裝@Many：實(shí)現(xiàn)一對多結(jié)果集封裝
MyBatis的增刪改查
我們完成簡單的user表的增刪改查的操作
private UserMapper userMapper;
@Before
public void before() throws IOException {
InputStream resourceAsStream = Resources.getResourceAsStream("SqlMapConfig.xml");
SqlSessionFactory sqlSessionFactory = new
SqlSessionFactoryBuilder().build(resourceAsStream);
SqlSession sqlSession = sqlSessionFactory.openSession(true);
userMapper = sqlSession.getMapper(UserMapper.class);
}
@Test
public void testAdd() {
User user = new User();
user.setUsername("測試數(shù)據(jù)");
user.setPassword("123");
user.setBirthday(new Date());
userMapper.add(user);
}
@Test
public void testUpdate() throws IOException {
User user = new User();
user.setId(16);
user.setUsername("測試數(shù)據(jù)修改");
user.setPassword("abc");
user.setBirthday(new Date());
userMapper.update(user);
}
@Test
public void testDelete() throws IOException {
userMapper.delete(16);
}
@Test
public void testFindById() throws IOException {
User user = userMapper.findById(1);
System.out.println(user);
}
@Test
public void testFindAll() throws IOException {
List<User> all = userMapper.findAll();
for(User user : all){
System.out.println(user);
}
}修改MyBatis的核心配置文件，我們使用了注解替代的映射文件，所以我們只需要加載使用了注解的Mapper接口即可
<mappers>
<!--掃描使用注解的類-->
<mapper class="com.zjq.mapper.UserMapper"></mapper>
</mappers>或者指定掃描包含映射關(guān)系的接口所在的包也可以
<mappers>
<!--掃描使用注解的類所在的包-->
<package name="com.zjq.mapper"></package>
</mappers>MyBatis的注解實(shí)現(xiàn)復(fù)雜映射開發(fā)
實(shí)現(xiàn)復(fù)雜關(guān)系映射之前我們可以在映射文件中通過配置來實(shí)現(xiàn)，使用注解開發(fā)后，我們可以使用@Results注解，@Result注解，@One注解，@Many注解組合完成復(fù)雜關(guān)系的配置
一對一查詢
一對一查詢的模型
用戶表和訂單表的關(guān)系為，一個用戶有多個訂單，一個訂單只從屬于一個用戶
一對一查詢的需求：查詢一個訂單，與此同時查詢出該訂單所屬的用戶
一對一查詢的語句
對應(yīng)的sql語句：
select * from orders; select * from user where id=查詢出訂單的uid;
創(chuàng)建Order和User實(shí)體
public class Order {
private int id;
private Date ordertime;
private double total;
//代表當(dāng)前訂單從屬于哪一個客戶
private User user;
}
public class User {
private int id;
private String username;
private String password;
private Date birthday;
}創(chuàng)建OrderMapper接口
public interface OrderMapper {
List<Order> findAll();
}使用注解配置Mapper
public interface OrderMapper {
@Select("select * from orders")
@Results({
@Result(id=true,property = "id",column = "id"),
@Result(property = "ordertime",column = "ordertime"),
@Result(property = "total",column = "total"),
@Result(property = "user",column = "uid",
javaType = User.class,
one = @One(select = "com.zjq.mapper.UserMapper.findById"))
})
List<Order> findAll();
}public interface UserMapper {
@Select("select * from user where id=#{id}")
User findById(int id);
}測試結(jié)果
@Test
public void testSelectOrderAndUser() {
List<Order> all = orderMapper.findAll();
for(Order order : all){
System.out.println(order);
}
}
一對多查詢
一對多查詢的模型
用戶表和訂單表的關(guān)系為，一個用戶有多個訂單，一個訂單只從屬于一個用戶
一對多查詢的需求：查詢一個用戶，與此同時查詢出該用戶具有的訂單
一對多查詢的語句
對應(yīng)的sql語句：
select * from user; select * from orders where uid=查詢出用戶的id;
修改User實(shí)體
public class Order {
private int id;
private Date ordertime;
private double total;
//代表當(dāng)前訂單從屬于哪一個客戶
private User user;
}
public class User {
private int id;
private String username;
private String password;
private Date birthday;
//代表當(dāng)前用戶具備哪些訂單
private List<Order> orderList;
}創(chuàng)建UserMapper接口
List<User> findAllUserAndOrder();
使用注解配置Mapper
public interface UserMapper {
@Select("select * from user")
@Results({
@Result(id = true,property = "id",column = "id"),
@Result(property = "username",column = "username"),
@Result(property = "password",column = "password"),
@Result(property = "birthday",column = "birthday"),
@Result(property = "orderList",column = "id",
javaType = List.class,
many = @Many(select = "com.zjq.mapper.OrderMapper.findByUid"))
})
List<User> findAllUserAndOrder();
}
public interface OrderMapper {
@Select("select * from orders where uid=#{uid}")
List<Order> findByUid(int uid);
}測試結(jié)果
List<User> all = userMapper.findAllUserAndOrder();
for(User user : all){
System.out.println(user.getUsername());
List<Order> orderList = user.getOrderList();
for(Order order : orderList){
System.out.println(order);
}
System.out.println("-----------------------------");
}
多對多查詢
多對多查詢的模型
用戶表和角色表的關(guān)系為，一個用戶有多個角色，一個角色被多個用戶使用
多對多查詢的需求：查詢用戶同時查詢出該用戶的所有角色
多對多查詢的語句
對應(yīng)的sql語句：
select * from user; select * from role r,user_role ur where r.id=ur.role_id and ur.user_id=用戶的id
創(chuàng)建Role實(shí)體，修改User實(shí)體
public class User {
private int id;
private String username;
private String password;
private Date birthday;
//代表當(dāng)前用戶具備哪些訂單
private List<Order> orderList;
//代表當(dāng)前用戶具備哪些角色
private List<Role> roleList;
}
public class Role {
private int id;
private String rolename;
}添加UserMapper接口方法
List<User> findAllUserAndRole();
使用注解配置Mapper
public interface UserMapper {
@Select("select * from user")
@Results({
@Result(id = true,property = "id",column = "id"),
@Result(property = "username",column = "username"),
@Result(property = "password",column = "password"),
@Result(property = "birthday",column = "birthday"),
@Result(property = "roleList",column = "id",
javaType = List.class,
many = @Many(select = "com.zjq.mapper.RoleMapper.findByUid"))
})
List<User> findAllUserAndRole();}
public interface RoleMapper {
@Select("select * from role r,user_role ur where r.id=ur.role_id and ur.user_id=#{uid}")
List<Role> findByUid(int uid);
}測試結(jié)果
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
List<User> all = mapper.findAllUserAndRole();
for(User user : all){
System.out.println(user.getUsername());
List<Role> roleList = user.getRoleList();
for(Role role : roleList){
System.out.println(role);
}
System.out.println("----------------------------------");
}
到此這篇關(guān)于MyBatis多表查詢和注解開發(fā)的文章就介紹到這了,更多相關(guān)MyBatis多表查詢內(nèi)容請搜索腳本之家以前的文章或繼續(xù)瀏覽下面的相關(guān)文章希望大家以后多多支持腳本之家！
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本文介紹如何在IDEA中配置Tomcat服務(wù)器,并創(chuàng)建Web項(xiàng)目,首先檢查Tomcat是否安裝完成,然后在IDEA中創(chuàng)建Web項(xiàng)目并添加Web結(jié)構(gòu),接著,配置編譯輸出路徑和依賴,將Tomcat的jar包復(fù)制到項(xiàng)目中,最后,配置Tomcat服務(wù)器并運(yùn)行項(xiàng)目,本文給大家介紹的非常詳細(xì),感興趣的朋友一起看看吧2025-01-01