Mybatis Plus official documentation has been very complete, why need to write such a document?

  • Official documents focus on the organization of knowledge structure, not on the learning sequence of learners
  • The cases in the official documents focus on API description, which is more suitable for learning MyBatis Plus and then referring to problems. It is not very friendly for beginners who use Mybatis for the first time.
  • The official documentation considers a comprehensive and complete introduction to Mybatis Plus, and I consider it from the perspective of “best practice”.
  • A lot of things in the world conform to the 2/8 principle, the purpose of this document is to help you extract the most important and most commonly used 20%, and quickly start using it! . The other 80% are not commonly used, free to go to the official documents to learn it!

Mybatis. Plus/Guide /

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Spring Boot integration Mybatis Plus

Importing dependencies through Maven coordinates

<! -- mybatis --> <dependency> <groupId>com.baomidou</groupId> <artifactId>mybatis-plus-boot-starter</artifactId> The < version > 3.1.2 < / version > < / dependency > <! -- mysql --> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <scope>runtime</scope> </dependency> <! -- lombok --> <dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <optional>true</optional> </dependency>Copy the code

Application Configures the data source and log output level

# configuration data source spring: a datasource: driver - class - name: the mysql. Cj.. JDBC driver url: JDBC: mysql: / / localhost: 3306 / mp? useUnicode=true&characterEncoding=utf8&serverTimezone=Asia/Shanghai username: test password: Fill in the database access password > < # configuration log logging: level: root: warn com. Zimug. Boot. Launch. Mapper: traceCopy the code

Step 3: Configure the packet scanning path of Mybatis Mapper class files

@SpringBootApplication
@MapperScan(basePackages = {"com.zimug.boot.launch.mapper"})
public class BootLaunchApplication {
    public static void main(String[] args) {
        SpringApplication.run(BootLaunchApplication.class, args);
    }
}Copy the code

Second, code to build entities and Mapper

Write entity class user.java, corresponding database table create SQL at the end of the text.

@data //lombok public class User {private Long ID; private String name; private Integer age; private String email; }Copy the code

Write the Mapper class usermapper.java

public interface UserMapper extends BaseMapper<User> {

}Copy the code

Basic CRUD use cases

3.1. Add a record

User user = new User(); User.setname (" Antetokounmpo "); user.setAge(18); int row = userMapper.insert(user); System.out.println(" count: "+row); System.out.println(" id: "+ user.getid ());Copy the code

After writing the above Java code, MP will automatically construct the following SQL to execute the database according to the Java code. Note: The primary key uses the snowflake algorithm by default

INSERT INTO user (id, name, age) VALUES (? ,? ,?)Copy the code

3.2. Delete a record based on the primary key

int rows = userMapper.deleteById(1170243901535006722L);
System.out.println("影响记录数：" + rows);Copy the code

1170243901535006722L is the ID generated according to the snowflake algorithm during data insertion

DELETE FROM user 
WHERE id=?Copy the code

3.3. Delete records based on conditions

// Construct conditional Map<String,Object> Map = new HashMap<>(); Map. Put ("name"," antetokounmpo "); map.put("age",18); Int rows = usermapper.deleteByMap (map); System.out.println(" rows: "+ rows);Copy the code
DELETE FROM user 
WHERE name = ? 
AND age = ?Copy the code

3.4. Query a data item by primary key

User user = userMapper.selectById(1089911557332887553L);
System.out.println(user);Copy the code
SELECT id,name,age,email
FROM user 
WHERE id=?Copy the code

3.5. Batch search data according to IDS

List<Long> ids = Arrays.asList(
    1087982257332887553L,
    1094590409767661570L,
    1094592041087729666L
);
List<User> list = userMapper.selectBatchIds(ids);
list.forEach(System.out::println);Copy the code
SELECT id,name,age,email FROM user WHERE id IN ( ? ,? ,?)Copy the code

3.6. Query information based on the specified parameters

Map<String, Object> map = new HashMap<>(); Map.put ("name", "Jone"); List<User> list = userMapper.selectByMap(map); list.forEach(System.out::println);Copy the code
SELECT id,name,age,email
FROM user 
WHERE name = ?Copy the code

3.7. Specify the query result field

1.

QueryWrapper<User> query = new QueryWrapper<>(); In ("age", arrays.asList (30, 31, 34, 35)). Last ("limit 1"); List<User> list = userMapper.selectList(query); list.forEach(System.out::println);Copy the code
SELECT name,age FROM user WHERE age IN (? ,? ,? ,?) LIMIT 1Copy the code

2.

QueryWrapper<User> query = new QueryWrapper<>(); Query. Like ("name", "J%").lt("age", 40).lt("age", 40).select("name", "age"); List<Map<String, Object>> maps = userMapper.selectMaps(query); maps.forEach(System.out::println);Copy the code
SELECT name,age 
FROM user 
WHERE name LIKE ? 
AND age < ?Copy the code

3.8. Modify data by primary key ID

User user = new User();
user.setId(1088248199570832385L);
user.setAge(18);
user.setEmail("[email protected]");

int rows = userMapper.updateById(user);
System.out.println("影响记录数：" + rows);Copy the code
UPDATE user SET age=? , email=? WHERE id=?Copy the code

3.9. Modify data according to UpdateWrapper custom conditions

UpdateWrapper<User> update = new UpdateWrapper<>(); update.eq("name", "Jack").eq("age", 28); //eq is the conditional constructor of MP, which stands for "equal" relation User User = new User(); user.setAge(29); user.setEmail("[email protected]"); int rows = userMapper.update(user, update); System.out.println(" rows: "+ rows);Copy the code
UPDATE user SET age=? , email=? WHERE name = ? AND age = ?Copy the code

Appendix — Test SQL:

DROP TABLE IF EXISTS user; CREATE TABLE user (id BIGINT(20) NOT NULL COMMENT 'id ', name VARCHAR(30) NULL DEFAULT NULL COMMENT' iD ', Age INT(11) NULL DEFAULT NULL COMMENT 'age ', email VARCHAR(50) NULL DEFAULT NULL COMMENT' mailbox ', PRIMARY KEY (ID));Copy the code

The corresponding database Data script is as follows:

DELETE FROM user;

INSERT INTO user (id, name, age, email) VALUES
(1, 'Jone', 18, '[email protected]'),
(2, 'Jack', 20, '[email protected]'),
(3, 'Tom', 28, '[email protected]'),
(4, 'Sandy', 21, '[email protected]'),
(5, 'Billie', 24, '[email protected]');Copy the code

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