MybatisPlus and code automatic generator

MybatisPlus

Introduction to MybatisPlus

MybatisPlus is an enhancement to the Mybatis framework. It does not change the content of the Mytatis framework. It just makes development more convenient and improves development efficiency. The addition, deletion, modification and query operations of single table queries have been encapsulated in MybatisPlus, and we do not need to write any more. For operations between multiple tables, we also need to write mapper and sql. Wrapper can be regarded as some conditions of encapsulation, including some code methods of sql statements, which are placed below.

Official page:https://baomidou.com/，Bottom side is its characteristics:

• Non-intrusive: only enhancements and no changes will be made, and will not affect existing projects.
• Powerful CRUD operation: Built-in universal Mapper, single-table CRUD operation can be implemented with a small amount of configuration
• Support Lambda: write query conditions without worrying about mistyping fields
• Support automatic generation of primary keys
• Built-in paging plugin

MybatisPlus basic configuration

MybatisPlus starting dependencies

   <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
        </dependency>

        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.4.2</version>
        </dependency>

Yaml configuration

spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://localhost:3306/mp_demo
    username: root
    password: root

Configure table name mapping

@Tablename("")

@Data
@NoArgsConstructor
@AllArgsConstructor
@Builder
@TableName("tbl_product")
public class Product {
    
    
    @TableId(value = "id",type = IdType.ASSIGN_ID)
//    @TableId(value = "id",type = IdType.AUTO)
    private Long id;
    private String pname;
    private String brand;
    private Double price;
    private Integer num;
    private Integer online;
    @TableField(fill = FieldFill.INSERT)
    private Date createTime;
    @TableField(fill = FieldFill.INSERT_UPDATE)
    private Date lastUpdateTime;
    private Integer version;
    private Integer deleted;

    @TableField(exist = false)
    private String desc;
}

Mapper inherits the BaseMapper<Entity Class> interface

//@Mapper
public interface ProductMapper extends BaseMapper<Product> {
    
    
}

The first MybatisPlus case

Automatically generate yml and startup classes—JBLSpringBootAppliacation plug-in

Service extends IService

In order to simplify service code writing, mybatisPlus provides a universal Service CRUD packageIServiceinterface

• Further encapsulate CRUD using get 查询单行 remove 删除 list 查询集合 page 分页 prefix naming method to distinguish Mapper layers to avoid confusion

Classification	method	describe
New	boolean save(T entity)	Added, entity object
	boolean saveOrUpdate(T entity)	If the id exists, update the record; if not, insert a record.
	boolean saveBatch(Collection entityList)	Insert (batch), 1000 pieces of data can be saved at a time by default
Revise	boolean updateById(T entity)	Modify by ID
	boolean update(T entity,Wrapper updateWrapper)	Modify according to conditions
Inquire	T getById(Serializable id)	Query by ID
	List listByIds(Collection idList)	Query (batch query based on ID)
	List list()	Search all
	List list(Wrapper queryWrapper)	Conditional query
delete	boolean removeById(Serializable id)	Delete by ID
	boolean removeByIds(Collection idList)	Delete (batch delete based on ID)
	boolean remove(Wrapper queryWrapper)	Delete based on conditions

public interface ProductService extends IService<Product> {
    
    
}

ServiceImpl extends ServiceImpl<Mapper,Pojo> implents Service

@Service
public class ProductServiceImpl extends ServiceImpl<ProductMapper, Product> implements ProductService {
    
    
}

Mapper extends BaseMapper

**BaseMapper<T>**：通用 CRUD 封装 `BaseMapper` 接口， 泛型 `T` 为任意实体对象

@Mapper
public interface ProductMapper extends BaseMapper<Product> {
    
    }

MyBatisPlus provides the Wrapper 条件构造器interface for setting conditions

• QueryWrapper LambdaQueryWrapper sets query and deletion conditions
• UpdateWrapper LambdaUpdateWrapper sets modification conditions

MP condition query API

AbstractWrapper provides a large number of methods for setting conditions

method	illustrate
eq （equals）	equal to =
ne （not equals）	Not equal to <>
gt (greater than)	Greater than>
ge (greater equals)	Greater than or equal to>=
lt (less than)	less than <
le (less equals)	Less than or equal to<=
between	between…and…
like	Fuzzy query LIKE
in	IN query
swimming	NOT IN query
isNull	NULL value query
isNotNull	IS NOT NULL
or	or

public interface ProductMapper extends BaseMapper<Product> {
    
    

}

Controller encapsulates Wrapper objects and query conditions

@Component
public class MyMateObjectHandler  implements MetaObjectHandler {
    
    
    @Override
    public void insertFill(MetaObject metaObject) {
    
    

        metaObject.setValue("createTime", new Date());

        metaObject.setValue("lastUpdateTime", new Date());

    }

    @Override
    public void updateFill(MetaObject metaObject) {
    
    

        metaObject.setValue("lastUpdateTime", new Date());


    }
}

Passed the test using PostMan

Four important notes

@TableName (table name)

When the entity class names corresponding to the database table are the same, they can also be omitted, mainly to establish a mapping relationship between the data table and the entity class.

yml global configuration TableName prefix (keyword table-prefix)

mybatis-plus:
  global-config:
    db-config:
      table-prefix: tbl_

@TableId (value="can be named if inconsistent", type= 3 common primary key auto-increment attributes 2 4 5 )

Mainly to set the auto-increment strategy of the primary key field in the data table. There are three common ones 2 4 5

value	describe
NONE	默认值Equivalent to INPUT+ASSIGN_ID
AUTO	Database primary key auto-increment
INPUT	Manually set primary key values
ASSIGN_ID	The corresponding type of the primary key can be a numeric type or a numeric type string The unique primary key is generated by the java client and the underlying layer is based on the snowflake algorithm
ASSIGN_UUID	The generated primary key value contains a string of numbers and lettersUUID Example: b463ec84690de187e3f9ad9229327d15

yml global configuration TableId (keyword id-type)

mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl #  标准注解
  global-config:
    db-config:
      table-prefix: tbl_
      id-type: auto

Annotation configuration (annotations will prevail in case of conflict)

When the id field and the attribute name are inconsistent, the value field can also be used for mapping.

    @TableId(value = "id",type = IdType.ASSIGN_ID)
    private Long id;

@TableFiled (4 common properties)

Attributes	type	default value	describe
value	String	“”	Database field name, you can omit it if it has the same name
exist	boolean	true	Whether it is a database table field. If the field does not exist in the table, it must be set to false. CRUD will not include this field.
fill	Enum	FieldFill.DEFAULT	Field auto-fill strategy, values ​​will not be auto-filled by default

value

Correspond between entity class attributes and database table fields

select（）

The default value is true, which can be set to false to specify a field not to be queried when querying, for example: password or sensitive field

exist（）

When there is a certain attribute on the attribute of the entity class but there is no corresponding field in the database table field, the setting can be false.

fill

Official sample code:https://baomidou.com/pages/4c6bcf/
Automatically fill in certain fields, such as create_time , there are several common values ​​(2 4 commonly used)

value	describe
DEFAULT	Not processed by default
INSERT	Populate fields on insert
UPDATE	Populate fields on update
INSERT_UPDATE	Populate fields on insert and update

@TableField(fill = FieldFill.INSERT)
private Date createTime;

@TableField(fill = FieldFill.INSERT_UPDATE)
private Date lastUpdateTime;

Autofill configuration class

package com.itheima.mp.config;

import com.baomidou.mybatisplus.core.handlers.MetaObjectHandler;
import lombok.extern.slf4j.Slf4j;
import org.apache.ibatis.reflection.MetaObject;
import org.springframework.stereotype.Component;

import java.util.Date;

@Slf4j
@Component
public class MyMetaObjectHandler implements MetaObjectHandler {
    
    

    @Override
    public void insertFill(MetaObject metaObject) {
    
    
        log.info("start insert fill ....");
        this.strictInsertFill(metaObject, "createTime", Date.class, new Date()); // 起始版本 3.3.0(推荐使用)
        this.strictInsertFill(metaObject, "lastUpdateTime", Date.class, new Date()); // 起始版本 3.3.0(推荐使用)
    }

    @Override
    public void updateFill(MetaObject metaObject) {
    
    
        log.info("start update fill ....");
        this.strictUpdateFill(metaObject, "lastUpdateTime", Date.class, new Date()); // 起始版本 3.3.0(推荐)

    }
}

@TableLogic (logical deletion)

Logical deletion: Set for data字段 to identify whether the data is available. The default status is available. When deleting, set the status field to unavailable and the data will still remain in the database

-- 删除改成更新状态
UPDATE tbl_product SET deleted=1 WHERE id=? AND deleted=0

-- 查询需要添加一个逻辑删除条件
SELECT * FROM tbl_product WHERE deleted=0

Add tombstone fields to table

Modify entity class

Add the corresponding field to the entity class, and use the @TableLogic annotation to identify this as a tombstone field

@TableLogic
private Integer deleted;

Global configuration logical deletion (keyword logic)

mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
  global-config:
    db-config:
      table-prefix: tbl_
      id-type: auto
      logic-delete-field: deleted
      logic-delete-value: 1
      logic-not-delete-value: 0

Pagination query plug-in

Mybatis has a built-in plug-in specifically for paging, which is very simple to use. It implements paging based on the interceptor principle.

Official sample code:https://baomidou.com/pages/97710a/#paginationinnerinterceptor

Add paging plugin interceptor

// MP配置类
@Configuration
public class MybatisPlusConfig {
    
    


     // MyBatisPlust拦截器配置
    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor() {
    
    
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        // 添加分页插件拦截器
        interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
        return interceptor;
    }

}

Pagination test

    @Test
    public void test() {
    
    

        Page<Product> page = new Page<>(2,5);  //分页参数

        LambdaQueryWrapper<Product> wrapper = new LambdaQueryWrapper();

        productMapper.selectPage(page, wrapper);// 返回那个page

        System.out.println(page.getTotal());

        List<Product> records = page.getRecords();

        records.forEach(System.out::println);
    }

Code generator

MybatisPlus plug-in

After installing the plug-in, restart an IDEA

Configure data source

code generation

You can click check filed to choose whether to generate a certain field

Mapper adds query supplementary exercises

Lambda expressions can be used

API

AbstractWrapper provides a large number of methods for setting conditions

method	illustrate
eq （equals）	equal to =
ne （not equals）	Not equal to <>
gt (greater than)	Greater than>
ge (greater equals)	Greater than or equal to>=
lt (less than)	less than <
le (less equals)	Less than or equal to<=
between	between…and…
like	Fuzzy query LIKE
in	IN query
swimming	NOT IN query
isNull	NULL value query
isNotNull	IS NOT NULL
or	or

Basic query

Query optimization - simplified judgments (there are a lot of if judgments in the query, simplify writing)

Query optimization-lambda query

Query Optimization-Chain Programming

Set query fields

group sort sort

Homework

Tips: Use the method name + return value type provided by BaseMpper to determine whether the requirements can be achieved

Exercise 1: Query the product name starting with OPPO, the price > 1500, and the product is on the shelf, the results are sorted in descending order by price selectList(wrapper)

    @Test
    public void test() {
    
    

        QueryWrapper<Product> wrapper = new QueryWrapper<>();

        wrapper.likeRight("pname", "OPPO")
                .gt("price",1500D)
                .eq("online","1")
                .orderByDesc("price");

        List<Product> products = productMapper.selectList(wrapper);

        products.forEach(System.out::println);

    }

Exercise 2: Query the product information whose id contains 1,2,6,8 and pname is not null and is on the shelves selectList(wrapper)

    @Test
    public void testDemo2() {
    
    
        QueryWrapper<Product> wrapper = new QueryWrapper<>();

        wrapper.in("id", "1", "2", "6", "8")
                .isNotNull("pname")
                .eq("online","1");

        List<Product> products = productMapper.selectList(wrapper);

        products.forEach(System.out::println);
    }

Exercise 3: Query product information whose ID contains 1,2,6,8 selectBatchIds(Collection)

@Test
public void testDemo3() {
    
    
    QueryWrapper<Product> wrapper = new QueryWrapper<>();

//    wrapper.like("id",1)
//            .or()
//           .like("id",2)
//            .or()
//            .like("id",6)
//            .or()
//            .like("id",8);

    List<Long> list = new ArrayList();
    list.add(1L);
    list.add(2L);
    list.add(6L);
    list.add(8L);
    List<Product> products = productMapper.selectBatchIds(list);
    products.forEach(System.out::println);
}

Exercise 4: Count the quantity of items with price > 5000 selectCount(wrapper)

@Test
public void testDemo4() {
    
    
    QueryWrapper<Product> wrapper = new QueryWrapper<>();

    wrapper.gt("price", 5000.0);
    int sum  = productMapper.selectCount(wrapper);

    System.out.println(sum);
}

Condition modification

conditional delete

Use updateWrapper and LambdaUpdateWrapper for modification
Query and delete using queryWrapper or LambdaQueryWrapper