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How to achieve the addition, deletion, modification and search of MybatisPlus, many novices are not very clear about this, in order to help you solve this problem, the following editor will explain for you in detail, people with this need can come to learn, I hope you can gain something.

Preface

In the persistence layer framework, there are many mybatis applications, and the proportion is gradually increasing. Usually the combination of projects is SSM. Mybatis is popular because it is flexible, easy to use and easy to optimize.

Mybatis directly executes the sql statement, and the sql statement is written in the xml file. Using mybatis requires multiple xml configuration files, which is more tedious to some extent. General database operations are related to CURD.

Mybatis-plus is an enhancement on mybatis, reducing the configuration of xml, almost without writing xml to achieve a single table CURD, which is very convenient and greatly provides the efficiency of development. We write programs to make life easier.

What is mybatis-plus?

MyBatis-Plus (MP for short) is an enhancement tool of MyBatis, which is only enhanced but not changed on the basis of MyBatis, in order to simplify development and improve efficiency.

MyBatis-Plus puts a coat on MyBatis, and almost all operations of single table CURD can be performed by MyBatis-Plus. And provides a variety of query methods, paging behavior. As a consumer, you don't need to write xml, just call the API provided by MyBatis-Plus.

Quick start

You can get started with MP in a few minutes, as long as you need to be familiar with mybatis,spring or spring boot, maven, and mastering lambda expressions can improve efficiency.

Prepare the environment:

Have Java development environment and corresponding IDE

Be familiar with Spring Boot

Be familiar with Maven

Prepare the data sheet

Create database user;use user;CREATE TABLE `user` (`id` int (11) NOT NULL AUTO_INCREMENT, `name` varchar (50) DEFAULT NULL, `email` varchar (80) DEFAULT NULL, `age` int (11) DEFAULT NULL, PRIMARY KEY (`id`) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;insert into user values (null,' Zhang San', '6666roomqq.compositure 18); configure maven in IDEA

Create a spring boot application

Quickly initialize a Spring Boot project using Spring Initializr

File-New Project in idea, fill in the project information after selecting Spring Initializr, and create the project.

Project information

Dependent selection of MyBatis Framework in SQL

Define the project name and path

Pom files add mybatis-plus dependencies

Com.baomidou mybatis-plus-boot-starter 3.0.5 mysql mysql-connector-java 8.0.25

Application.properties or application.yml add database configuration

Spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driverspring.datasource.url=jdbc:mysql://127.0.0.1:3306/userspring.datasource.username=rootspring.datasource.password=root

Or

Spring: datasource: driver-class-name: com.mysql.cj.jdbc.Driver url: jdbc:mysql://127.0.0.1:3306/user username: root password: root

Create an entity class

@ TableId sets the primary key. IdType.AUTO uses automatic growth to generate the primary key.

Create a mapper interface

Inherit BaseMapper in MyBatis Plus, use methods in MP in UserMapper, real

Now CURD.

Add @ MapperScan scan Mapper folder

test

View the database

Configure mybatis log mybatis-plus: configuration: log-impl: org.apache.ibatis.logging.stdout.StdOutImpl

Basic usage of CRUD

The operation of CRUD comes from the methods in BaseMapper. There are 17 methods in BaseMapper, and there are many methods with different parameters for CRUD operations. Inherits the methods that BaseMapper can have.

List of BaseMapper methods:

Insert operation

Note: insert () returns the value int, the number of rows in which the data was successfully inserted, and the number of successful records. GetId () gets the primary key value and automatically assigns the primary key value to the primary key id of the entity class after successfully affecting the number of rows.

Update operation

Update the previous database

Updated database

Note: the fields of null are not updated

The field of email is not set, so the field of email at this time is null

The SQL statement does not set email

Database

Delete operation

There are several ways to delete

DeleteById: press primary key to delete

Delete according to the condition in Map

Note: the deletion condition is encapsulated in Map, key is the column name, value is the value, and multiple key are connected by and.

Log:

Batch deletion

Put the id to be deleted into List and pass it to deleteBatchIds ()

Journal

Select operation

Note: if there is no query result, no error will be reported.

Journal

Batch query records

Note: according to the id query record, store multiple id to be queried into List and call selectBatchIds ()

Journal

Conditional queries using Map

Put the conditional field to be queried to Map,key is the field, and value is the conditional value. Multiple conditions are and joins. Call selectByMap (), pass in Map as a parameter, and the return value is the List collection.

Journal

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