After using mybatisplus, I haven't written SQL for a long time

Java fish 2021-09-15 06:58:42
using mybatisplus haven written sql

I heard that wechat search 《Java Young fish 》 It's going to change !

This article is included in github and gitee , There's my whole Java Series articles , Study or interview can see oh

( One ) Preface

First write JDBC When , To manually configure the connection information , Write one by one sql sentence . later Mybatis There is , There is no need to manually configure the connection information ,sql Statements are also isolated from code , But I have to write Sql. Then there was MybatisPlus, This next company Sql No need to write .

( Two ) What is? MybatisPlus

First, take out the official website address :

simply ,MybatisPlus yes Mybatis Enhanced tools for , Simplify the development , Improve development efficiency . In the website , He used such a picture to show MybatisPlus and Mybatis The relationship between .

In the picture ,MybatisPlus Indicates that it and Mybatis The relationship between them is like two brothers in a soul fight , They don't affect each other , But it can make it easier for you to fight monsters .

( 3、 ... and ) Lead to

In the interpretation of the MybatisPlus Before , Let's prepare a batch of data first

USE user;
SET NAMES utf8mb4;
`user_id` varchar(64) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT ' user Id',
`username` varchar(32) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT ' user name ',
`password` varchar(32) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT ' password ',
`gmt_create` datetime(3) NOT NULL COMMENT ' Creation time ',
`gmt_modified` datetime(3) NOT NULL COMMENT ' Modification time ',
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci;
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( Four )Mybatis Quick start

1、 Introduce the latest dependencies

<version>Latest Version</version>
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2、 Configure database connection information in the configuration center

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3、 stay Spring Add in startup class MapperScan annotation

public class MybatisPlusApplication {
public static void main(String[] args) {, args);
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4、 establish mapper,DO

MybatisPlus Can be generated automatically Mapper、DO、Service、Controller, Here's a tutorial , Manual establishment .MybatisPlus and Mybatis The first difference , Use here @TableName The annotation indicates which table the current entity class corresponds to

public class UserDO {
private Long id;
private String userId;
private String username;
private String password;
private LocalDateTime gmtCreate;
private LocalDateTime gmtModified;
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establish Mapper Class time , Inherit BaseMapper class , This is a MybatisPlus Provides a base class , Encapsulates common query operations

public interface UserMapper extends BaseMapper<UserDO> {
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5、 Query data

In the use of Mybatis when , Data CRUD All need to be written sql Can achieve ,MybatisPlus Provided BaseMapper Both provide Mapper Layer encapsulation interface , And provides Service Layer encapsulation interface . Based on the previous writing , In normal development, we tend to use Mapper The interface of the layer Introduce Mapper Several interfaces at the level :

For example, I want to inquire user The amount of data in the table , I can call :

Integer integer = userMapper.selectCount(null);
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MybatisPlus Provides a condition constructor Wrappers, Can pass Wrappers Construct a series of conditions , Such as query username by name1 The data of

List<UserDO> userDOList = userMapper.selectList(Wrappers.<UserDO>lambdaQuery()
.eq(UserDO::getUsername, "name1"));
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Another example is that I want to query id Greater than 5 The data of

List<UserDO> userDOList1 = userMapper.selectList(Wrappers.<UserDO>lambdaQuery()
.gt(UserDO::getId, 5));
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6、 Insert data into

There is no problem using the above method for data query , There are several things you can optimize when inserting data , We can use an annotation @TableId Set the auto increment method of the primary key , Can pass @TableField Annotation sets the automatic filling of data . So modify UserDO This class :

public class UserDO {
@TableId(type = IdType.AUTO)
private Long id;
private String userId;
private String username;
private String password;
@TableField(fill = FieldFill.INSERT)
private LocalDateTime gmtCreate;
@TableField(fill = FieldFill.INSERT_UPDATE)
private LocalDateTime gmtModified;
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In entity classes , Set up id Self increasing , Set up gmtCreate Auto fill on insert , Set up gmtModified Automatically fill in when creating and modifying , Then configure auto fill rules :

public class MybatisObjectHandler implements MetaObjectHandler {
public void insertFill(MetaObject metaObject) {
public void updateFill(MetaObject metaObject) {
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Finally, call API insert data

public void test3(){
UserDO userDO=new UserDO();
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For more query methods, please refer to the official website , Very detailed . But if yours sql The operation of connecting tables involving multiple tables , You can still talk to yourself MyBatis Same handwriting sql.

( 5、 ... and ) summary

thus , You should be right. MybatisPlus Have a general understanding of , Another thing worth mentioning MybatisPlus The open source organization Baomi bean is a domestic organization , Therefore, this document is particularly friendly to domestic developers , Safe to use . I'm a fish , See you next time !

本文为[Java fish]所创,转载请带上原文链接,感谢

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