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This article will explain in detail the example analysis of multi-table operation and annotation development of the Mybatis framework in Java. The editor thinks it is very practical, so I share it with you for reference. I hope you can get something after reading this article.

One-to-one query

Model of one-to-one query

The relationship between the user table and the order table is that a user has multiple orders, and an order belongs to only one user.

Demand for one-to-one query: query an order and at the same time find out who the order belongs to

One-to-one query statement

The corresponding sql statement: select * from orders ojournal user u where o.uidqiu.id; the result of the query is as follows:

Create Order and User entities

Create an OrderMapper interface

Public interface OrderMapper {/ / query all methods public List findAll ();}

Configure OrderMapper.xml

SELECT *, o.id oid FROM orders omega user u WHERE o.uid=u.id

Configure UserMapper.xml

SELECT *, o.id oid FROM USER uorder o WHERE u.id=o.uid SELECT * FROM USER uMagazine syscraper usernames role ur,sys_role r WHERE u.id=ur.userId AND ur.roleId=r.id

Configure sqlMapConfig.xml

Test code

@ Test public void test1 () throws IOException {InputStream resourceAsStream = Resources.getResourceAsStream ("sqlMapConfig.xml"); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder () .build (resourceAsStream); SqlSession sqlSession = sqlSessionFactory.openSession (); OrderMapper mapper = sqlSession.getMapper (OrderMapper.class); List orderList = mapper.findAll (); for (Order order: orderList) {System.out.println (order);} sqlSession.close () }

One-to-many query

One-to-many query model

The relationship between the user table and the order table is that a user has multiple orders, and an order only belongs to the one-to-many query needs of one user: query a user, and at the same time query the orders that the user has.

The corresponding sql statement: select *, o.id oid from user u left join orders o on u.iddistribuo.uid; the result of the query is as follows:

SELECT *, o.id oid FROM USER u, orders o WHERE u.id=o.uid

Modify User solid

Create a UserMapper interface

Configure UserMapper.xml

Test result

Many-to-many query

Many-to-many query model

The relationship between the user table and the role table is that a user has multiple roles, and a role is used by multiple users for many-to-many queries: query users query all roles of the user at the same time.

Many-to-many query statement

The corresponding sql statement: select u.recording journal r.recording journal r.id rid from user u left join user_role ur on u.id=ur.user_idinner join role r on ur.role_id=r.id

The query results are as follows:

Create Role entities and modify User entities

Add UserMapper interface method

Configure UserMapper.xml (above)

Test code

Summary:

MyBatis multi-table configuration method:

One-to-one configuration: using for configuration

One-to-many configuration: use + for configuration

Many-to-many configuration: use + for configuration

Annotation development of Mybatis

Common notes on Mybatis

Annotation development has become more and more popular in recent years, and Mybatis can also use annotation development, so we can write fewer Mapper mapping files. We first learn around some basic CRUD, and then learn about complex mapping multi-table operations.

@ Insert: add

@ Update: implement update @ Delete: implement deletion @ Select: implement query

@ Result: implement result set encapsulation

@ Results: can be used with @ Result to encapsulate multiple result sets @ One: achieve one-to-one result set encapsulation

@ Many: implement one-to-many result set encapsulation

Private UserMapper mapper; @ Before public void before () throws IOException {InputStream resourceAsStream = Resources.getResourceAsStream ("sqlMapConfig.xml"); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder () .build (resourceAsStream); SqlSession sqlSession = sqlSessionFactory.openSession (true); mapper = sqlSession.getMapper (UserMapper.class);} @ Test public void testSave () {User user = new User (); user.setUsername ("tom") User.setPassword ("abc"); mapper.save (user);} @ Test public void testUpdate () {User user = new User (); user.setId (18); user.setUsername ("lucy"); user.setPassword ("123"); mapper.update (user);} @ Test public void testDelete () {mapper.delete (18) @ Test public void testFindById () {User user = mapper.findById (2); System.out.println (user);} @ Test public void testFindAll () {List all = mapper.findAll (); for (User user: all) {System.out.println (user);}}

To modify the core configuration file of MyBatis, we use a mapping file instead of annotations, so we only need to load the Mapper interface that uses annotations

Or you can specify the package that scans the interface that contains the mapping relationship.

UserMapper:

Public interface UserMapper {@ Insert ("insert into user values (# {id}, # {username}, # {password}, # {birthday})") public void save (User user); @ Update ("update user set username=# {username}, password=# {password} where id=# {id}") public void update (User user); @ Delete ("delete from user where id=# {id}") public void delete (int id) @ Select ("select * from user where id=# {id}") public User findById (int id); @ Select ("select * from user") public List findAll () @ Select ("select * from user") @ Results ({@ Result (id=true, column = "id", property = "id"), @ Result (column = "username", property = "username"), @ Result (column = "password", property = "password"), @ Result (property = "orderList", column = "id") JavaType = List.class, many = @ Many (select = "com.longdi.mapper.OrderMapper.findByUid")}) public List findUserAndOrderAll () @ Select ("SELECT * FROM USER") @ Results ({@ Result (id = true,column = "id", property = "id"), @ Result (column = "username", property = "username"), @ Result (column = "password", property = "password"), @ Result (property = "roleList", column = "id") JavaType = List.class, many = @ Many (select = "com.longdi.mapper.RoleMapper.findByUid")}) public List findUserAndRoleAll () } annotations of MyBatis to realize complex mapping development

Before implementing complex relationship mapping, we can configure it in the mapping file. After developing with annotations, we can use @ Results annotation, @ Result annotation, @ One annotation and @ Many annotation to complete the configuration of complex relationship.

One-to-one query (configure Mapper with annotations)

Test the code:

One-to-many queries (configure Mapper with annotations)

Test code

Many-to-many queries (configure mapper with annotations)

Test the code:

On the "Java Mybatis framework multi-table operation and annotation development example analysis" this article is shared here, I hope the above content can be of some help to you, so that you can learn more knowledge, if you think the article is good, please share it out for more people to see.

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