Shulou(Shulou.com)06/03 Report--

Many novices are not very clear about how Mybatis uses @ one and @ Many to implement one-to-one and one-to-many related queries. In order to help you solve this problem, the following editor will explain it in detail. People with this need can come and learn. I hope you can get something.

First, the preparatory work 1. Create a springboot project with the following structure

two。 Add pom.xml configuration information org.mybatis mybatis 3.4.2 org.mybatis.spring.boot mybatis-spring-boot-starter 1.3.0 mysql mysql-connector-java 5.1.34 3. Configuration related information

Modify the suffix of the default application.properties file to ".yml", that is, the configuration file name is: application.yml, and configure the following information:

Spring: # DataSource data source datasource: url: jdbc:mysql://localhost:3306/mybatis_test?useSSL=false& username: root password: root driver-class-name: com.mysql.jdbc.Driver#MyBatis configuration mybatis: type-aliases-package: com.mye.hl07mybatis.api.pojo # alias definition configuration: log-impl: org.apache.ibatis.logging.stdout.StdOutImpl # specify the specific implementation of the log used by MyBatis Map-underscore-to-camel-case is automatically found when not specified: true # enables automatic hump naming rule (camel case) mapping lazy-loading-enabled: true # turns on delay loading switch aggressive-lazy-loading: false # changes positive loading to negative loading (that is, on-demand loading). The default value is false lazy-load-trigger-methods: "# blocking irrelevant operation triggers Implement lazy loading cache-enabled: true # turn on the global cache switch (secondary environment). The default value is true 2. Use @ One annotation to implement one-to-one relational query.

Requirements: get user information and get a list of one-to-many associated permissions

1. Create a user information table (tb_user) in the MySQL database

-- determine whether the data table exists, and delete the DROP TABLE IF EXISTS tb_user if it exists. -- create "user Information" data sheet CREATE TABLE IF NOT EXISTS tb_user (user_id INT AUTO_INCREMENT PRIMARY KEY COMMENT 'user number', user_account VARCHAR (50) NOT NULL COMMENT 'user account', user_password VARCHAR (50) NOT NULL COMMENT 'user password', blog_url VARCHAR (50) NOT NULL COMMENT 'blog address' Remark VARCHAR (50) COMMENT 'remarks') COMMENT = 'user information table' -- add data INSERT INTO tb_user (user_account,user_password,blog_url,remark) VALUES ('blog refusing to stay up late', '123456' https://blog.csdn.net/weixin_43296313/','', Welcome to visit blog that refuses to stay up late)

two。 Create ID card information table (tb_idcard) in MySQL database

-- determine whether the data table exists, then delete DROP TABLE IF EXISTS tb_idcard;-- create the "ID card information" data table CREATE TABLE IF NOT EXISTS tb_idcard (id INT AUTO_INCREMENT PRIMARY KEY COMMENT'ID card ID', user_id INT NOT NULL COMMENT 'user number', idCard_code VARCHAR (45) COMMENT'ID card number') COMMENT = "ID card information table" -- add data INSERT INTO tb_idcard (user_id,idCard_code) VALUE (1meme 123456789')

3. Create a user information persistence class (UserInfo.java)

@ Data@AllArgsConstructor@NoArgsConstructorpublic class UserInfo {private int userId; / / user ID private String userAccount; / / user account private String userPassword; / / user password private String blogUrl; / / blog address private String remark; / / remarks private IdcardInfo idcardInfo; / / ID card information}

4. Create a persistence class for ID card information (IdcardInfo.java)

@ Data@AllArgsConstructor@NoArgsConstructorpublic class IdcardInfo {public int id; / / ID card ID public int userId; / / user ID public String idCardCode; / / ID card number}

5. Create UserMapper interface (Mapper dynamic proxy interface for user information)

@ Repository@Mapperpublic interface UserMapper {/ * get user information and ID card information * one-to-one related query * / @ Select ("SELECT * FROM tb_user WHERE user_id = # {userId}") @ Results (id = "userAndIdcardResultMap", value = {@ Result (property = "userId", column = "user_id", javaType = Integer.class, jdbcType = JdbcType.INTEGER, id = true) @ Result (property = "userAccount", column = "user_account", javaType = String.class, jdbcType = JdbcType.VARCHAR), @ Result (property = "userPassword", column = "user_password", javaType = String.class, jdbcType = JdbcType.VARCHAR), @ Result (property = "blogUrl", column = "blog_url", javaType = String.class, jdbcType = JdbcType.VARCHAR), @ Result (property = "remark", column = "remark" JavaType = String.class, jdbcType = JdbcType.VARCHAR), @ Result (property = "idcardInfo", column = "user_id", one = @ One (select = "com.mye.hl07mybatis.api.mapper.UserMapper.getIdcardInfo", fetchType = FetchType.LAZY)}) UserInfo getUserAndIdcardInfo (@ Param ("userId") int userId) / * according to the user ID Obtain ID card information * / @ Select ("SELECT * FROM tb_idcard WHERE user_id = # {userId}") @ Results (id = "idcardInfoResultMap", value = {@ Result (property = "id", column = "id"), @ Result (property = "userId", column = "user_id"), @ Result (property = "idCardCode") Column = "idCard_code")}) IdcardInfo getIdcardInfo (@ Param ("userId") int userId) }

6. Implement the mapping relationship between entity classes and data tables

Add @ MapperScan (basePackages = "com.mye.hl07mybatis.api.mapper") to the SpringBoot startup class.

@ SpringBootApplication@MapperScan (basePackages = "com.mye.hl07mybatis.api.mapper") public class Hl07MybatisApplication {public static void main (String [] args) {SpringApplication.run (Hl07MybatisApplication.class, args);}}

7. Write an execution method to obtain user information and ID card information (one-to-one related query)

@ SpringBootTest (classes = Hl07MybatisApplication.class) @ RunWith (SpringRunner.class) public class Hl07MybatisApplicationTests {@ Autowired private UserMapper userMapper; / * get user information and ID card information * one-to-one related query * @ author pan_junbiao * / @ Test public void getUserAndIdcardInfo () {/ / execute the query method of Mapper proxy object UserInfo userInfo = userMapper.getUserAndIdcardInfo (1) / / print result if {System.out.println ("user ID:" + userInfo.getUserId ()); System.out.println ("user account:" + userInfo.getUserAccount ()); System.out.println ("user password:" + userInfo.getUserPassword ()); System.out.println ("blog address:" + userInfo.getBlogUrl ()) System.out.println ("remarks:" + userInfo.getRemark ()); System.out.println ("- -"); / / get ID card information IdcardInfo idcardInfo = userInfo.getIdcardInfo () If {System.out.println ("ID card ID:" + idcardInfo.getId ()); System.out.println ("user ID:" + idcardInfo.getUserId ()); System.out.println ("ID card number:" + idcardInfo.getIdCardCode ());}

Execution result:

Third, use @ Many annotation to implement one-to-many associative query

Requirements: get user information and get a list of one-to-many associated permissions

1. Create a permission information table (tb_role) in the MySQL database

-- determine whether the data table exists, and delete DROP TABLE IF EXISTS tb_role; if it exists-- create the "permission information" data table CREATE TABLE IF NOT EXISTS tb_role (id INT AUTO_INCREMENT PRIMARY KEY COMMENT 'permission ID', user_id INT NOT NULL COMMENT' user number', role_name VARCHAR (50) NOT NULL COMMENT 'permission name') COMMENT = "permission information table" INSERT INTO tb_role (user_id,role_name) VALUES (1) 'system administrator'), (1 'news administrator'), (1 'advertisement administrator')

two。 Create a permission information persistence class (RoleInfo.java)

@ Data@AllArgsConstructor@NoArgsConstructorpublic class RoleInfo {private int id; / / permission ID private int userId; / / user number private String roleName; / / permission name}

3. Modify the user information persistence class (UserInfo.java) to add the property field of the permission list

@ Data@AllArgsConstructor@NoArgsConstructorpublic class UserInfo {private int userId; / / user ID private String userAccount; / / user account private String userPassword; / / user password private String blogUrl; / / blog address private String remark; / / remarks private IdcardInfo idcardInfo; / / ID card information private List roleInfoList; / / permission list}

4. Write Mapper dynamic proxy interface (UserMapper.java) for user information

/ * * get user information and permission list * one-to-many related query * @ author pan_junbiao * / @ Select ("SELECT * FROM tb_user WHERE user_id = # {userId}") @ Results (id = "userAndRolesResultMap", value = {@ Result (property = "userId", column = "user_id", javaType = Integer.class, jdbcType = JdbcType.INTEGER, id = true), @ Result (property = "userAccount", column = "user_account") JavaType = String.class, jdbcType = JdbcType.VARCHAR), @ Result (property = "userPassword", column = "user_password", javaType = String.class, jdbcType = JdbcType.VARCHAR), @ Result (property = "blogUrl", column = "blog_url", javaType = String.class, jdbcType = JdbcType.VARCHAR), @ Result (property = "remark", column = "remark", javaType = String.class, jdbcType = JdbcType.VARCHAR), @ Result (property = "roleInfoList") Column = "user_id", many = @ Many (select = "com.pjb.mapper.UserMapper.getRoleList", fetchType = FetchType.LAZY)}) public UserInfo getUserAndRolesInfo (@ Param ("userId") int userId) / * according to the user ID Get permission list * @ author pan_junbiao * / @ Select ("SELECT * FROM tb_role WHERE user_id = # {userId}") @ Results (id = "roleInfoResultMap", value = {@ Result (property = "id", column = "id"), @ Result (property = "userId", column = "user_id"), @ Result (property = "roleName", column = "role_name")) public List getRoleList (@ Param ("userId") int userId)

5. Write execution methods to get user information and permission list (one-to-many associated queries)

/ * get user information and permission list * one-to-many association query * @ author pan_junbiao * / @ Test public void getUserAndRolesInfo () {/ / execute the query method of Mapper proxy object UserInfo userInfo = userMapper.getUserAndRolesInfo (1) / / print result if {System.out.println ("user ID:" + userInfo.getUserId ()); System.out.println ("user account:" + userInfo.getUserAccount ()); System.out.println ("user password:" + userInfo.getUserPassword ()); System.out.println ("blog address:" + userInfo.getBlogUrl ()) System.out.println ("remarks:" + userInfo.getRemark ()); System.out.println ("- -"); / / get permission list List roleInfoList = userInfo.getRoleInfoList () If (roleInfoListrated permissions null & & roleInfoList.size () > 0) {System.out.println ("permissions owned by the user:"); for (RoleInfo roleInfo: roleInfoList) {System.out.println (roleInfo.getRoleName ());}}

Execution result:

IV. The difference between FetchType.LAZY and FetchType.EAGER

FetchType.LAZY: lazy loading. Properties that define lazy loading are not immediately loaded from the database when an entity is loaded.

FetchType.EAGER: when an entity is loaded, the properties that define the emergency load are immediately loaded from the database.

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