MyBatisPlus conditional constructor MyBatisPlus conditional constructor MyBatisPlus conditional constructor

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MyBatisPlus profile

A list,

MyBatis-Plus (MP for short) is a MyBatis enhancement tool, on the basis of MyBatis only do enhancement do not change, to simplify the development and improve efficiency.

Second, the characteristics of

No intrusion: only enhancements are made, no changes are made, and its introduction will not affect the existing project, as smooth as silk
Low loss: Basic CURD will be injected automatically upon startup, with basically no loss in performance and direct object-oriented operation
Powerful CRUD operations: built-in universal Mapper, universal Service, only through a small amount of configuration can achieve a single table most CRUD operations, more powerful — conditional constructor, to meet all types of use requirements
Support Lambda form call: through Lambda expressions, it is convenient to write all kinds of query conditions, without worrying about field write errors
Supports multiple databases: supports MySQL, MariaDB, Oracle, DB2, H2, HSQL, SQLite, Postgre, SQLServer2005, SQLServer and other databases
Support automatic generation of primary keys: support up to four primary key policies (including distributed unique ID generator – Sequence), can be freely configured, perfect solution to the primary key problem
Support for XML hot loading: Mapper’s CORRESPONDING XML supports hot loading and can even start without XML for simple CRUD operations
Support for ActiveRecord mode: Support for ActiveRecord form calls, entity classes only need to inherit from Model classes to perform powerful CRUD operations
Support custom global universal operations: support Write once (use anywhere)
Support automatic keyword escape: support database keywords (order, key……) Automatic escape, but also custom keywords
Built-in code generator: using code or Maven plug-in can quickly generate Mapper, Model, Service, Controller layer code, support template engine, more than a lot of custom configuration you to use
Built-in paging plug-in: Based on MyBatis physical paging, developers do not need to care about specific operations, after configuring the plug-in, write paging is equal to ordinary List query
Built-in performance analysis plug-in: outputs Sql statements and their execution time. It is recommended to enable this function during development and testing to quickly find out slow queries
Built-in global interception plug-in: provides intelligent analysis and blocking of delete and UPDATE operations on all tables, and can customize interception rules to prevent misoperations
Built-in Sql injection stripper: supports Sql injection stripper to effectively prevent Sql injection attacks

Introduction to MyBatisPlus

Use Spring Initializr to quickly initialize a Spring Boot project

Add dependencies

Mybatis -plus-boot-starter, MySQL

<! --mybatis-plus--> <dependency> <groupId>com.baomidou</groupId> <artifactId>mybatis-plus-boot-starter</artifactId> The < version > 3.0.5 < / version > < / dependency > <! --mysql--> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> </dependency>Copy the code

Three, configuration,

Add the MySQL database configuration to the application.properties configuration file

spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost:3306/mybatis_plus? serverTimezone=GMT%2B8
spring.datasource.username=root
spring.datasource.password=yky
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Fourth, code writing

1. Mapper inherits BaseMapper interface

@Mapper
public interface StudentMapper extends BaseMapper<tStudent> {}Copy the code

2. Entity classes

Note the relationship between database table names and entity class names:

3. Start classes

5. Configure logs

Console output SQL statement:

Core profile configuration

# mybatis log mybatis - plus. The configuration. The log - impl = org. Apache. Ibatis. Logging. Stdout. StdOutImplCopy the code

Six, test,

@SpringBootTest
public class Mybatisplusdemo01ApplicationTests {

    @Autowired
    private StudentMapper studentMapper;

    @Test
    void contextLoads(a) {
        List<tStudent> students = studentMapper.selectList(null);
        for(tStudent s : students) { System.out.println(s); }}}Copy the code

CRUD interface of MyBatisPlus

A, the insert

1. Insert operation

Simply call the methods in the BaseMapper interface

// Insert operations
	@Test
	public  void  add(a){
		tStudent student = new tStudent();
		student.setName("A little tramp who likes to code.");
		student.setAge(19);
		studentMapper.insert(student);
	}
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2. Primary key policy

(1) ID_WORKER

MyBatis-Plus default primary key policy is:ID_WORKERGlobally unique ID

(2) Self-increment strategy

To add a primary key automatically, configure the following primary key policies
1. Primary key increment needs to be set at table creation time
2. In the entity field@TableId(type = IdType.AUTO)

 @TableId(type = IdType.AUTO)
    private Integer id;
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To affect the configuration of all entities, you can set the global primary key configuration

Mybatis -plus.global-config.db-config.id-type=autoCopy the code

Other primary key strategies:

Second, the update

1. Update by Id

@Test
public void updateStudent(a) {
    tStudent student = new tStudent();
    student.setId(1009);
    student.setName("Invincible in the East");
    studentMapper.updateById(student);
}
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2. Automatic filling

(1) Add automatic fill field in database table

(2) Add annotations to entities

// Auto-fill
@TableField(fill = FieldFill.INSERT)
private Date create_time;
@TableField(fill = FieldFill.INSERT_UPDATE)
private Date update_time;
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(3) Realize the meta-object processor interface

Note: Don’t forget to add the @Component annotation

@Component
public class MyMateObjectHandler implements MetaObjectHandler {

    @Override
    public void insertFill(MetaObject metaObject) {
        this.setFieldValByName("update_time".new Date(),metaObject);
        this.setFieldValByName("create_time".new Date(),metaObject);
    }

    @Override
    public void updateFill(MetaObject metaObject) {
        this.setFieldValByName("update_time".newDate(),metaObject); }}Copy the code

Matters needing attention

Fields must be declaredTableFieldAnnotation, attributefillSelect the corresponding policy, this statement tells Mybatis-Plus to reserve the injection of SQL fields
Filling processorMyMetaObjectHandlerDeclaration is required in Spring Boot@Componentor@Beaninjection
To distinguish FieldFill. XXX from the field name and field type, strictInsertFill or strictUpdateFill methods of the parent class must be used
There is no need to distinguish between the fillStrategy methods that can use the parent class

3. Optimistic Locking

Main solution: lost update, that is, to achieve thread-safe data update

1. Implementation of optimistic lock:

When the record is fetched, the current version is retrieved
When you update, take this version with you
When performing an update, set version = newVersion where version = oldVersion
If the version is incorrect, the update fails

2. Configuration Steps:

The plug-in configuration

   /** * Optimistic lock plug-in */
    @Bean
    public OptimisticLockerInterceptor optimisticLockerInterceptor(a) {
        return new OptimisticLockerInterceptor();
    }
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Add the @Version annotation to the version attribute in the entity class

/ / optimistic locking
    @TableField(fill = FieldFill.INSERT)
    @Version
    private Integer version;
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3. Special notes

Support for data types only int, Integer, long, long, the Date and Timestamp, LocalDateTime
In the integer format, newVersion = oldVersion + 1
NewVersion is written back to the entity
Only updateById(ID) and Update (Entity, Wrapper) methods are supported
The wrapper cannot be reused under the Update (Entity, wrapper) method!

Third, the select

1. Query records based on the ID

@Test
	void selecttStudentById(a) {
		tStudent students = studentMapper.selectById(1004);
		System.out.println(students);
	}
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2. Batch query information using multiple ids

@Test
void selecttStudentById(a) {
	List<tStudent> tStudents = studentMapper.selectBatchIds(Arrays.asList(1001.1002.1003));
	System.out.println(tStudents );
}
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3, simple conditional query

Map encapsulates query conditions

Note: Keys in the map correspond to column names in the database.

@Test
public void testSelectByMap(a){

    HashMap<String, Object> map = new HashMap<>();
    map.put("name"."A little tramp who likes to code.");
    map.put("age".19);
    List<User> users = userMapper.selectByMap(map);
    users.forEach(System.out::println);
}
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4, paging query

MyBatis Plus has its own paging plug-in, as long as the simple configuration can achieve paging function

Add a paging plug-in to the configuration class

 @Bean
    public PaginationInterceptor paginationInterceptor(a) {
        PaginationInterceptor paginationInterceptor = new PaginationInterceptor();
        // Set the request page to be larger than the maximum page operation, true to return to the home page, false to continue the request default false
        // paginationInterceptor.setOverflow(false);
        // Set the maximum number of pages per page, default 500, -1 is not limited
        // paginationInterceptor.setLimit(500);
        // Enable count join optimization for only part of the left join
        paginationInterceptor.setCountSqlParser(new JsqlParserCountOptimize(true));
        return paginationInterceptor;
    }
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Use of paging plug-ins

Create page object

// Create a Page object
	// Two parameters: the current page and the number of records displayed per page
	Page<tStudent> studentPage = new Page<>(1.3);
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2, by calling the paging query method

@Test
public void pageHander(a){
	// Create a Page object
	// Two parameters: the current page and the number of records displayed per page
	Page<tStudent> studentPage = new Page<>(1.3);
	// Call the paging query method
	// Encapsulate all paging data into a page object
	studentMapper.selectPage(studentPage,null);
	studentPage.getCurrent();/ / the current page
	studentPage.getRecords();// A list of data per page
	studentPage.getSize();// Display the number of records per page
	studentPage.getTotal();// Total number of records
	studentPage.getPages();/ / the total number of pages
	System.out.println(studentPage.getPages());
	studentPage.hasNext();// Determine if there is a next page
	studentPage.hasPrevious();// Check if there is a previous page
}
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Fourth, the delete

1. Delete records based on id

@Test
public void testDeleteById(a){
    int result = userMapper.deleteById(8L);
    System.out.println(result);
}
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2. Delete them in batches

  @Test
    public void testDeleteBatchIds(a) {
        int result = userMapper.deleteBatchIds(Arrays.asList(8.9.10));
        System.out.println(result);
    }
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3, simple condition query delete

@Test
public void testDeleteByMap(a) {

    HashMap<String, Object> map = new HashMap<>();
    map.put("name"."Helen");
    map.put("age".18);

    int result = userMapper.deleteByMap(map);
    System.out.println(result);
}
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4. Logical deletion

Physical delete: Deletes the data from the database. The deleted data cannot be queried later
Logical deletion: False deletion. The state of the field representing whether the data is deleted or not is changed to deleted state. After that, the data record can still be seen in the database

(1) Add the deleted field to the database

(2) Add @tablelogic

 @TableLogic
    @TableField(fill = FieldFill.INSERT)
    private Integer deleted;
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(3) Automatically fill in the deleted default value when new data is added

You do not need to set the default value when adding a deleted field in the database

this.setFieldValByName("deleted".0,metaObject);
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(4) Application. Properties add configuration (optional)

#mybatis-plus.global-config.db-config.logic-delete-value=1 #mybatis-plus.global-config.db-config.logic-not-delete-value=0Copy the code