Improve productivity, the most complete MyBatisPlus explanation!

Hello everyone, I am xiao CAI, a desire to do CAI Not CAI xiao CAI in the Internet industry. Soft but just, soft praise, white piao just! Ghost ~ remember to give me a three – even oh!

This paper mainly introduces the use of MybatisPlus

Refer to it if necessary

If it is helpful, do not forget the Sunday

Wechat public number has been opened, xiao CAI Liang, did not pay attention to the students remember to pay attention to oh!

If you’re still writing CRUD SQL over and over again every day, and if you’re getting tired of it, why not spend some time reading this article and revamping your existing projects? You’ll reap the benefits!

First, what is MP

MP full name of Mybatis-Plus, as the official explanation is to become Mybatis best partner, referred to as gay friends. It is on the basis of MyBatis only do enhancement do not change, in order to simplify development, improve efficiency and born.

1. Three major features

1) Be silent

Just make enhancements without making changes, and introduce it without affecting existing projects, as smooth as silk.

2) Efficiency is Paramount

Single table CRUD operations can be performed quickly with simple configuration, resulting in significant time savings.

3) Rich functionality

Code generation, physical paging, performance analysis, and more.

2. Support databases

Mysql, Mariadb, Oracle, DB2, H2, HSQL, SQLite, PostgresQL, SQLServer, Presto, Gauss, Firebird
Phoenix, Clickhouse, Sybase ASE, OceanBase, Dameng Database, Virtual Valley database, DDA Jincang database, NANJING University general database

3. Frame structure

To be honest, the above content as long as you open the official website can also see, so we will first to practical operation!

Two, MP combat

1. Hand to hand exercises

1) Database and table preparation

The SQL statement:

use test;
CREATE TABLE `student`  (
  `id` int(0) NOT NULL AUTO_INCREMENT,
  `dept_id` int(0) NULL DEFAULT NULL,
  `name` varchar(16) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NULL DEFAULT NULL,
  `remark` varchar(32) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NULL DEFAULT NULL.PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 7 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_bin ROW_FORMAT = Dynamic;
-- ----------------------------
-- Records of student
-- ----------------------------
INSERT INTO `student` VALUES (1.1.'side'.'Pay attention to small dishes don't get lost! ');
INSERT INTO `student` VALUES (2.2.'Ming'.'Good good study, day day up! ');
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2) POM dependency

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-test</artifactId>
</dependency>
<! --lombok-->
<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.16.16</version>
</dependency>
<! - MP plug-in - >
<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.2.0</version>
</dependency>
<! --Mysql-->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.21</version>
</dependency>
<! -- Connection pool -->
<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>druid</artifactId>
    <version>1.2.1</version>
</dependency>
<! --JUNIT-->
<dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.13.1</version>
</dependency>
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3) Configuration files

spring:
  datasource:
    url: jdbc:mysql://localhost:3306/test
    username: root
    password: 123456
    driver-class-name: com.mysql.cj.jdbc.Driver
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4) Entity classes

@Data
@Builder
@TableName("student")
public class User {

    @TableId(type = IdType.AUTO)
    private Integer id;

    private Integer deptId;

    private String name;

    private String remark;
}
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5) Mapper

public interface UserMapper extends BaseMapper<User> {}
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6) Test classes

@RunWith(SpringRunner.class)
@SpringBootTest
public class MapperTest {

    @Autowired
    private UserMapper userMapper;

    @Test
    public void getAll(a) {
        List<User> users = userMapper.selectList(null); users.forEach(System.out::println); }}/** OUTPUT: User(id=1, deptId=1, name= small, remark= small) User(id= 1, deptId=1, name= 2, remark= 1) * * /
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Dishes:

In the above result, we can see that we have printed out all the data in the database (two pieces). The selectList() method is used in userMapper. Usermapper inherits the BaseMapper interface. This interface is what MybatisPlus provides, so let’s look at what methods this interface provides.

2. The CRUD operation

1) insert

@Test
public void insert(a) {
    // This uses lombok's Builder pattern to build objects
    User user = User.builder().deptId(1).name("Wah").remark("Xiao Hua loves learning").build();
    int insertFlag = userMapper.insert(user);
    log.info("Insert influence line number, {} | xiaohua ID: {}", insertFlag, user.getId());
}
/ * * the OUTPUT: insert influence lines, 1 | xiaohua ID: 8 * * /
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You can see that not only did we insert the data, but we also got the ID of the inserted data, but it is worth noting that the ID here is self-increasing, but not the default ID generation strategy of MP, but the one we specified in the entity class:

The following primary key generation strategies are supported in MP:

Now that we’ve seen the @TableID annotation, let’s focus on a common annotation @tableField

As you can see from the annotation name, @tableID is used to mark the primary key ID, and @tableField is used to mark other fields.

As you can see, there are a lot of values in this annotation. Here are some common values:

value

Use @tableField (value=”describe”) for resolving inconsistent field names and hump naming, such as when the attribute name in an entity class is Remark, but the field name in a table is describe. If there is a hump name configured globally, this place is not written.

exist

For fields that do not exist in the table, we can mark them with @tableField (exist = false)

condition

@tablefield (condition = sqlcondition.like); Select name LIKE CONCAT(‘%’, value,’%’) where SqlCondition = ‘%’;

update

Update table name set field = “%s+1” where %s will fill the field

select

If the remark field is text and you do not want to query it, you can use @tableField (select = false) to constrain the query

2) update

There are two types of update operations for MybatisPlus:

int updateById(Param("et") T entity);

int update(@Param("et") T entity, @Param("ew") Wrapper<T> updateWrapper);
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Update by ID

@Test
public void update(a) {
    User user = User.builder().id(3).name("Wah").remark("Xiao Hua loves playing games.").build();
    userMapper.updateById(user);
}
/** Update result: User(id=3, deptId=1, name= xiaohu, remark= Xiaohu) **/
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Update according to conditions

@Test
public void update(a) {
    UpdateWrapper<User> updateWrapper = new UpdateWrapper<>();
    updateWrapper.eq("name"."Wah").set("remark"."Xiao Hua loves playing chess.");
    userMapper.update(null, updateWrapper);
}
/** update result: User(id=3, deptId=1, name=小华, remark=小华) **/
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We can also put the condition to be updated into the user object:

@Test
public void update(a) {
    UpdateWrapper<User> updateWrapper = new UpdateWrapper<>();
    updateWrapper.eq("name"."Wah");
    User user = User.builder().remark("Xiao Hua loves swimming.").build();
    userMapper.update(user, updateWrapper);
}
/** update result: User(id=3, deptId=1, name=小华, remark=小华 love to bathe) **/
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3) the delete

There are more ways to delete in MybatisPlus than to update. There are four ways in total:

int deleteById(Serializable id);

int deleteByMap(@Param("cm") Map<String, Object> columnMap);

int delete(@Param("ew") Wrapper<T> wrapper);

int deleteBatchIds(@Param("coll") Collection<? extends Serializable> idList);
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Delete by ID

@Test
public void deleteById(a) {
    userMapper.deleteById(3);
}
/** DELETE FROM student WHERE id = 3; * * /
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Delete from Map

@Test
public void deleteByMap(a) {
    HashMap<String, Object> columnMap = new HashMap<>();
    columnMap.put("name"."Wah");
    columnMap.put("remark"."Xiao Hua loves swimming.");
    userMapper.deleteByMap(columnMap);
}
/** SQL语句：
DELETE FROM student WHRE name = '小华' AND remark = '小华爱游泳';
**/
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Delete from Wrapper

@Test
public void delete(a) {
    UpdateWrapper<User> wrapper = new UpdateWrapper<>();
    wrapper.eq("remark"."Xiao Hua loves playing chess.");
    userMapper.delete(wrapper);
}
/** SQL statement: DELETE FROM student WHRE remark = ' '; * * /
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There is another way to wrap an entity class directly in a Wrapper according to Wrapper deletion:

@Test
public void delete(a) {
    User user = User.builder().remark("Xiao Hua loves playing chess.").build();
    UpdateWrapper<User> wrapper = new UpdateWrapper<>(user);
    userMapper.delete(wrapper);
}
/** SQL statement: DELETE FROM student WHRE remark = ' '; * * /
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Delete data in batches based on the ID

@Test
public void deleteBatchIds(a) {
    List<Integer> idList = new ArrayList<>();
    idList.add(4);
    idList.add(7);
    userMapper.deleteBatchIds(idList);
}
/** SQL statement: DELETE FROM student WHERE id In (4,7) **/
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4) select

Query operation is the most frequently used in our development, is also the most important. MybatisPlus also supports many query methods, as follows:

T selectById(Serializable id);

List<T> selectBatchIds(@Param("coll") Collection<? extends Serializable> idList);

List<T> selectByMap(@Param("cm") Map<String, Object> columnMap);

T selectOne(@Param("ew") Wrapper<T> queryWrapper);

Integer selectCount(@Param("ew") Wrapper<T> queryWrapper);

List<T> selectList(@Param("ew") Wrapper<T> queryWrapper);

List<Map<String, Object>> selectMaps(@Param("ew") Wrapper<T> queryWrapper);

List<Object> selectObjs(@aram("ew") Wrapper<T> queryWrapper);

IPage<T> selectPage(IPage<T> page, @Param("ew") Wrapper<T> queryWrapper);

IPage<Map<String, Object>> selectMapsPage(IPage<T> page, @Param("ew") Wrapper<T> queryWrapper);
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You can see that there are 10 methods, and we’re going to test them one by one

Query all

@Test
public void selectList(a) {
    List<User> users = userMapper.selectList(null);
    users.forEach(System.out::println);
}
/** OUTPUT: User(id=1, deptId=1, name= small, remark= small) User(id= 1, deptId=1, name= 2, remark= 1) SELECT id, dept_id, name, remark FROM student; * * /
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The number of queries

@Test
public void selectCount(a) {
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    queryWrapper.like("name"."Small");
    System.out.println(userMapper.selectCount(queryWrapper));
}
/** OUTPUT: 2 SQL: SELECT COUNT(1) FROM student WHERE (name LIKE '% % %'); * * /
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Query by ID

@Test
public void selectById(a) {
    User user = userMapper.selectById(1);
    System.out.println(user);
}
/** OUTPUT: User(id=1, deptId=1, name= small, remark= small) SELECT id, dept_id, name, remark FROM student WHERE id = 1; * * /
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Batch query information by ID

@Test
public void selectBatchIds(a) {
    List<User> users = userMapper.selectBatchIds(Arrays.asList(1.2));
    users.forEach(System.out::println);
}
/** OUTPUT: User(id=1, deptId=1, name= small, remark= small) User(id= 1, deptId=1, name= 2, remark= 1) SELECT id, dept_id, name, remark FROM student WHERE id IN (1, 2); * * /
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Query a single item by condition

@Test
public void selectOne(a) {
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    queryWrapper.eq("name"."Dishes");
    User user = userMapper.selectOne(queryWrapper);
    System.out.println(user);
}
/** OUTPUT: User(id=1, deptId=1, name= small, remark= small) SELECT id, name, dept_id, remark FROM student WHERE (name = '小 dish '); * * /
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Query multiple entries based on conditions

Pass parameters through map, not by LIKE query, but by = query

@Test
public void selectByMap(a) {
    HashMap<String, Object> columnMap = new HashMap<>();
    columnMap.put("name"."Small");
    List<User> users = userMapper.selectByMap(columnMap);
    users.forEach(System.out::println);
}
/** OUTPUT: null SQL statement: SELECT id, name, dept_id, remark FROM student WHERE name = 'small '; * * /
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If we don’t create a new entity class to encapsulate the result, we can also use a Map to receive the result set:

@Test
public void selectMaps(a) {
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    queryWrapper.like("name"."Small");
    List<Map<String, Object>> maps = userMapper.selectMaps(queryWrapper);
    maps.forEach(System.out::println);
}
/** OUTPUT: {name= small, remark= small , id=1, dept_id=1} {name= xiaoming, remark= study hard, day day up! SELECT id, name, dept_id, remark FROM student WHERE (name LIKE '% % %'); * * /
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We can also use an Object to receive a result set:

@Test
public void selectObjs(a) {
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    queryWrapper.like("name"."Small");
    List<Object> objects = userMapper.selectObjs(queryWrapper);
}
/** OUTPUT: {name= small, remark= small , id=1, dept_id=1} {name= xiaoming, remark= study hard, day day up! SELECT id, name, dept_id, remark FROM student WHERE (name LIKE '% % %'); * * /
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Paging query

@Test
public void selectPage(a) {
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    queryWrapper.like("name"."Small");
    Page<User> page = new Page<>(1.1);
    IPage<User> userIPage = userMapper.selectPage(page, queryWrapper);
    System.out.println("Total data :" + userIPage.getTotal());
    System.out.println("Total pages :" + userIPage.getPages());
    System.out.println("Current page :" + userIPage.getCurrent());
    System.out.println("Page size :" + userIPage.getSize());
    userIPage.getRecords().forEach(System.out::println);
}
/** OUTPUT: data (id=1, deptId=1, name= small, remark= small) /** OUTPUT: data (id=1, deptId=1, remark= small) SELECT id, name, dept_id, remark FROM student WHERE (name LIKE '% % %') LIMIT 0,1; * * /
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3. Conditional constructor

In CRUD’s basic operations, conditional queries are wrapped in the Wrapper class, simply using eq and like operations. In fact, this class is quite powerful, and we’ll look at it in more detail below.

1) allEq

Full eq or individual isNull

allEq(Map<R, V> params)
allEq(Map<R, V> params, boolean null2IsNull)
allEq(boolean condition, Map<R, V> params, boolean null2IsNull)
    
allEq(BiPredicate<R, V> filter, Map<R, V> params)
allEq(BiPredicate<R, V> filter, Map<R, V> params, boolean null2IsNull)
allEq(boolean condition, BiPredicate<R, V> filter, Map<R, V> params, boolean null2IsNull) 
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Parameter Description:

Param: key indicates the database field name and value indicates the field value

**nullsIsNull: if ** is true, isNull is called when map value isNull; if false, isNull is ignored when map value isNull

Filter: the filter function that determines whether fields are allowed to enter the matching condition

Example:

allEq(Map<R, V> params)

@Test
public void testAllEq(a) {
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    Map<String,Object> params = new HashMap<>();
    params.put("name"."Dishes");
    params.put("dept_id".1);
    params.put("remark".null);
    queryWrapper.allEq(params); // The isNull method is called
    userMapper.selectList(queryWrapper);
}
SELECT id,name,dept_id,remark FROM student WHERE (name = '小菜' AND dept_id = 1 AND remark IS NULL); * * /
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allEq(Map<R, V> params, boolean null2IsNull)

@Test
public void testAllEq(a) {
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    Map<String,Object> params = new HashMap<>();
    params.put("name"."Dishes");
    params.put("dept_id".1);
    params.put("remark".null);
    queryWrapper.allEq(params, false); // The isNull method is not called
    userMapper.selectList(queryWrapper);
}
/** result: User(id=1, deptId=1, name=小 题, remark= 小 题) SELECT id,name,dept_id,remark FROM student WHERE (name = '小 dish 'AND dept_id = 1); * * /
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allEq(boolean condition, Map<R, V> params, boolean null2IsNull)

@Test
public void testAllEq(a) {
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    Map<String,Object> params = new HashMap<>();
    params.put("name"."Dishes");
    params.put("dept_id".1);
    params.put("remark".null);
    queryWrapper.allEq(false,params,false);	// do not enter the condition to query
    userMapper.selectList(queryWrapper);
}
/** result: {name=小 题, remark= 小 题 , id=1, dept_id=1} {name= xiaoming, remark= study hard, day day up! SELECT id,name,dept_id,remark FROM student; * * /
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allEq(BiPredicate<R, V> filter, Map<R, V> params)

@Test
public void testAllEq(a) {
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    Map<String, Object> params = new HashMap<>();
    params.put("name"."Dishes");
    params.put("dept_id".1);
    params.put("remark".null);
    // Only key containing "m" is used as a conditional judgment
    queryWrapper.allEq((k, v) -> (k.contains("m")), params);
    userMapper.selectList(queryWrapper);
}
SELECT id,name,dept_id,remark FROM student WHERE (name = '小菜' AND remark IS NULL); * * /
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2) Comparison operation

Eq:The equivalent of=
Ne:The equivalent of! =
Gt:The equivalent of>
Ge:The equivalent of> =
Lt:The equivalent of<
Le:The equivalent of< =
Between:The equivalent of between ... and ...
NotBetween:The equivalent ofnot between ... and ...
In:The equivalent ofin(.. . ,..)
NotIn:The equivalent ofnot in(.. . ,..)

3) Fuzzy query

Like: Like ("name"," xiaocai ") --> name like "% xiaocai %"
NotLike: NotLike ("name","小小 ") --> name not like "%小小"
LikeLeft: Like ("name"," xiaocai ") --> name like "% xiaocai"
LikeRight: Like ("name"," xiaoxiao ") --> name like "xiaoxiao %"

4) sorting

OrderBy:

orderBy(boolean condition, boolean isAsc, R... columns)
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orderBy(true, true, "id", "name") --> order by id ASC, name ASC

OrderByAsc:

orderByAsc("id","name") --> order by id ASC, name ASC

OrderByDesc:

orderByDesc("id","name) --> order by id Desc, name Desc

5) Logical query

Or:

Concatenation: An active call to or indicates that the next method is not concatenated with and! (don’t call the or is the default for the use of the and connection), eq. (” id “, 1) or (.) eq (” name “, “king”)

Nesting: OR (I -> I.E Q (“name”, “Li Bai “).ne(” Status “,” Alive “)

And:

Nested: and (I – > appropriate precautions q (” name “, “li bai”). Ne (” status “, “live”))

6) select

Select (“id”, “name”); select(“id”, “name”);

4. Configuration description

1) Basic configuration

configLocation

Specifies the location of **MyBatis ** config file. If we have MyBatis configuration file, we need to configure the path of the configuration file to configLocation

SpringBoot:

mybatis-plus.config-location = classpath:mybatis-config.xml
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For SpringMvc:

<bean id="sqlSessionFactory"
class="com.baomidou.mybatisplus.extension.spring.MybatisSqlSessionFactoryBean">
<property name="configLocation" value="classpath:mybatis-config.xml"/>
</bean
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mapperLocations

Mapper is used to specify the location of the XML file corresponding to Mapper. Mapper is directly inherited from BaseMapper provided by MP in general CRUD. We can also customize methods and then customize SQL in XML files. In this case, we need to tell Mapper the location of the corresponding XML file

SpringBoot:

mybatis-plus.mapper-locations = classpath*:mybatis/*.xml
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For SpringMVC:

<bean id="sqlSessionFactory"
class="com.baomidou.mybatisplus.extension.spring.MybatisSqlSessionFactoryBean">
<property name="mapperLocations" value="classpath*:mybatis/*.xml"/>
</bean>
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typeAliasesPackage

For MyBatis alias package scan path, through this attribute can be registered to the package class alias, after registration in Mapper corresponding XML file can directly use the class name, instead of using the fully qualified class name

SpringBoot:

mybatis-plus.type-aliases-package = cbuc.life.bean
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For SpringMVC:

<bean id="sqlSessionFactory"
class="com.baomidou.mybatisplus.extension.spring.MybatisSqlSessionFactoryBean">
<property name="typeAliasesPackage"
value="com.baomidou.mybatisplus.samples.quickstart.entity"/>
</bean>
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2) Advanced configuration

mapUnderScoreToCamelCase

The default value of this configuration is true, but the default value of this property in MyBatis is false, so we will enable this configuration in normal development.

This parameter cannot be used with mybatis-plus.config-location
mybatis-plus.configuration.map-underscore-to-camel-case = false
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cacheEnabled

Globally turn on or off any caches that have been configured by all mappers in the configuration file, default to true.

mybatis-plus.configuration.cache-enabled = false
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3) DB policy configuration

idType

The global default primary key type can be set to omit the @tableID (type = idtype.auto) configuration in the entity object. The default value for this configuration is ID_WORKER

SpringBoot:

mybatis-plus.global-config.db-config.id-type = auto
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For SpringMVC:

<bean id="sqlSessionFactory"
class="com.baomidou.mybatisplus.extension.spring.MybatisSqlSessionFactoryBean">
	<property name="dataSource" ref="dataSource"/>
    <property name="globalConfig">
        <bean class="com.baomidou.mybatisplus.core.config.GlobalConfig">
            <property name="dbConfig">
                <bean         class="com.baomidou.mybatisplus.core.config.GlobalConfig$DbConfig">
                	<property name="idType" value="AUTO"/>
                </bean>
            </property>
        </bean>
    </property>
</bean>
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tablePrefix

TableName prefix, after global configuration can omit @tablename () configuration. The default value for this configuration is NULL

SpringBoot:

mybatis-plus.global-config.db-config.table-prefix = yq_
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For SpringMVC:

<bean id="sqlSessionFactory"
class="com.baomidou.mybatisplus.extension.spring.MybatisSqlSessionFactoryBean">
    <property name="dataSource" ref="dataSource"/>
    <property name="globalConfig">
        <bean class="com.baomidou.mybatisplus.core.config.GlobalConfig">
            <property name="dbConfig">
                <bean            class="com.baomidou.mybatisplus.core.config.GlobalConfig$DbConfig">
                	<property name="idType" value="AUTO"/>
                	<property name="tablePrefix" value="yq_"/>
                </bean>
            </property>
        </bean>
    </property>
</bean>
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5. Other extensions

1) Automatic filling

Sometimes we want some fields to fill in automatically when inserting or updating data. For example, we usually have fields such as insert time or update time in the data table, and we will fill them with the current time by default. We can also configure them in MP.

First we need the annotation @tableField (fill = FieldFill.INSERT) to fill in at INSERT time.

@TableField(fill = FieldFill.INSERT)
private String remark;
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The auto-fill mode is as follows:

public enum FieldFill {
    /** ** does not process */ by default
    DEFAULT,
    /** * Fill in the field */ when inserting
    INSERT,
    /** * Fill in the field */ when updating
    UPDATE,
    /** * Fill the fields */ when inserting and updating
    INSERT_UPDATE
}
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Then we write a custom fill processing mode:

@Component
public class MyMetaObjectHandler implements MetaObjectHandler {
    @Override
    public void insertFill(MetaObject metaObject) {
        Object remark = getFieldValByName("remark", metaObject);
        if (null == remark) {
            setFieldValByName("remark"."Study hard.", metaObject); }}@Override
    public void updateFill(MetaObject metaObject) {
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Testing:

@Test
public void testObjectHandler(a) {
    User user = User.builder().deptId(1).name("Xiao Ming").build();
    userMapper.insert(user);
}
/** SQL statement: INSERT INTO student (name, dept_id, remark) VALUES ('小明', 1, '三 明'); * * /
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You can see that when we insert, the fields we filled are automatically merged in.

2) Logical deletion

In the development, most of the time, we do not need to delete data in the real sense of physical deletion, but use logical deletion. In this way, we need state conditions when querying, to ensure that the marked data is not queried. MP also supports this functionality.

We need to add a field status to the student table to declare whether the data has been deleted, 0 for deleted, 1 for not deleted, and then we need to add this property to the entity class as well:

@TableLogic
private Integer status;
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In application.yaml:

mybatis-plus:
  global-config:
    db-config:
      logic-delete-value: 0
      logic-not-delete-value: 1
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Testing:

@Test
public void testLogicDelete(a) {
    userMapper.deleteById(1);
}
UPDATE student SET status=0 WHERE id=1 AND status=1; * * /
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SQL > delete SQL > delete SQL > delete SQL > delete SQL > delete SQL > delete SQL > delete SQL > delete SQL

3) General enumeration

If there is a gender field, we usually use 0 and 1 to represent it, but if there is a gender field, we need to convert the value. We can use enumeration to solve the problem:

Add a sex field to student to indicate gender, 0 for female, 1 for male, and define an enumeration class:

public enum SexEnum implements IEnum<Integer> {
    MAN(1."Male"),
    WOMEN(0."Female");

    private int code;

    private String value;

    SexEnum(int code, String value) {
        this.code = code;
        this.value = value;
    }

    @Override
    public Integer getValue(a) {
        return this.code;
    }
    
    // Be careful to override this method, otherwise the value will be converted to 'MAN' instead of 'male'
    @Override
    public String toString(a) {
        return this.value; }}Copy the code

Then add the corresponding attribute to the entity class:

private SexEnum sex;
Copy the code

In application.yaml:

mybatis-plus:
  type-enums-package: cbuc.life.enums
Copy the code

Testing:

@Test
public void selectOne(a) {
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    queryWrapper.eq("name"."Dishes");
    User user = userMapper.selectOne(queryWrapper);
    System.out.println(user);
}
User(id=1, deptId=1, name=小 题, remark= 小 题) SELECT id,sex,name,dept_id,remark,status FROM student WHERE status=1 AND (name = '小 dish '); * * /
Copy the code

END

That’s the end of this article, it’s a bit long, but if you can read it in its full form, I’m sure you’ll be able to use MybatisPlus pretty well! The road is long, xiao CAI seeks together with you!

Today you work harder, tomorrow you will be able to say less words!

I am xiao CAI, a man who studies with you. 💋

Wechat public number has been opened, xiao CAI Liang, did not pay attention to the students remember to pay attention to oh!

Improve productivity, the most complete MyBatisPlus explanation!

First, what is MP

1. Three major features

1) Be silent

2) Efficiency is Paramount

3) Rich functionality

2. Support databases

3. Frame structure

Two, MP combat

1. Hand to hand exercises

1) Database and table preparation

2) POM dependency

3) Configuration files

4) Entity classes

5) Mapper

6) Test classes

2. The CRUD operation

1) insert

2) update

Update by ID

Update according to conditions

3) the delete

Delete by ID

Delete from Map

Delete from Wrapper

Delete data in batches based on the ID

4) select

Query all

The number of queries

Query by ID

Batch query information by ID

Query a single item by condition

Query multiple entries based on conditions

Paging query

3. Conditional constructor

1) allEq

2) Comparison operation

3) Fuzzy query

4) sorting

5) Logical query

6) select

4. Configuration description

1) Basic configuration

2) Advanced configuration

3) DB policy configuration

5. Other extensions

1) Automatic filling

2) Logical deletion

3) General enumeration

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