Primary Key Generation Strategy

In MyBatis-Plus, the primary key generation strategy is an important concept that determines how to generate unique primary key values for records in database tables. Below is a detailed explanation and configuration methods for primary key generation strategies.

Overview of Primary Key Generation Strategy

The primary key generation strategy must use the INPUT type, which means the primary key value needs to be provided by the user when inserting data. MyBatis-Plus supports defining the @KeySequence annotation in a parent class, which can be inherited and used by child classes.

Starting from version 3.3.0, MyBatis-Plus automatically recognizes the primary key type, so manual specification of the primary key type is no longer required.

MyBatis-Plus natively supports primary key generation strategies for various databases, including:

• DB2KeyGenerator
• H2KeyGenerator
• KingbaseKeyGenerator
• OracleKeyGenerator
• PostgreKeyGenerator

If the built-in primary key generation strategies do not meet your requirements, you can extend custom primary key generation strategies by implementing the IKeyGenerator interface.

Example

Here is an example of an entity class using the @KeySequence annotation:

@KeySequence(value = "SEQ_ORACLE_STRING_KEY", clazz = String.class)
public class YourEntity {

    @TableId(value = "ID_STR", type = IdType.INPUT)
    private String idStr;

    // Other fields and methods...
}

In this example, the YourEntity class uses the @KeySequence annotation to specify the sequence SEQ_ORACLE_STRING_KEY in an Oracle database to generate primary key values, with the primary key type being String.

Spring Boot Configuration

Method 1: Using a Configuration Class

In a Spring Boot application, you can set the primary key generation strategy via a configuration class:

@Bean
public IKeyGenerator keyGenerator() {
    return new H2KeyGenerator();
}

Method 2: Customizing via MybatisPlusPropertiesCustomizer

You can also customize the primary key generation strategy using MybatisPlusPropertiesCustomizer:

@Bean
public MybatisPlusPropertiesCustomizer plusPropertiesCustomizer() {
    return plusProperties -> plusProperties.getGlobalConfig().getDbConfig().setKeyGenerator(new H2KeyGenerator());
}

Spring Configuration

Method 1: XML Configuration

In traditional Spring applications, you can set the primary key generation strategy via XML configuration:

<bean id="globalConfig" class="com.baomidou.mybatisplus.core.config.GlobalConfig">
   <property name="dbConfig" ref="dbConfig"/>
</bean>

<bean id="dbConfig" class="com.baomidou.mybatisplus.core.config.GlobalConfig.DbConfig">
   <property name="keyGenerator" ref="keyGenerator"/>
</bean>

<bean id="keyGenerator" class="com.baomidou.mybatisplus.extension.incrementer.H2KeyGenerator"/>

Method 2: Annotation Configuration

Configure the primary key generation strategy using annotations:

@Bean
public GlobalConfig globalConfig() {
    GlobalConfig conf = new GlobalConfig();
    conf.setDbConfig(new GlobalConfig.DbConfig().setKeyGenerator(new H2KeyGenerator()));
    return conf;
}

The above configuration methods allow you to choose the appropriate way to set the primary key generation strategy based on your project requirements.