Auto-fill Fields

MyBatis-Plus provides a convenient auto-fill feature for automatically populating certain fields during data insertion or updates, such as creation time and update time. Below is a detailed explanation of how to use this feature.

Overview of the Principle

The auto-fill feature is implemented by the com.baomidou.mybatisplus.core.handlers.MetaObjectHandler interface. You need to create a class that implements this interface and define the fill logic for insertion and updates within it.

Steps to Use

1. Define the Entity Class

In the entity class, use the @TableField annotation to mark which fields require auto-filling and specify the fill strategy.

public class User {
    @TableField(fill = FieldFill.INSERT)
    private String createTime;

    @TableField(fill = FieldFill.UPDATE)
    private String updateTime;

    // Other fields...
}

2. Implement MetaObjectHandler

Create a class that implements the MetaObjectHandler interface and override the insertFill and updateFill methods.

// java example
@Slf4j
@Component
public class MyMetaObjectHandler implements MetaObjectHandler {

    @Override
    public void insertFill(MetaObject metaObject) {
        log.info("Start insert fill...");
        this.strictInsertFill(metaObject, "createUserId", Long.class, 123456L)
        this.strictInsertFill(metaObject, "createTime", LocalDateTime.class, LocalDateTime.now());
    }

    @Override
    public void updateFill(MetaObject metaObject) {
        log.info("Start update fill...");
        this.strictInsertFill(metaObject, "updateUserId", Long.class, 123456L)
        this.strictUpdateFill(metaObject, "updateTime", LocalDateTime.class, LocalDateTime.now());
    }
}

// kotlin example
@Component
class MyMetaObjectHandler : MetaObjectHandler {

    private val log = LoggerFactory.getLogger(MyMetaObjectHandler::class.java)

    // Note: To convert Kotlin types to Java types, use xxx::class.javaObjectType to prevent certain types from being converted to primitive types, which may cause fill failures.
    override fun insertFill(metaObject: MetaObject) {
        log.info("Start insert fill...");
        this.strictInsertFill(metaObject, "createUserId", Long::class.javaObjectType, 123456L)
        this.strictInsertFill(metaObject, "createTime", LocalDateTime::class.javaObjectType, LocalDateTime.now())
    }

    override fun updateFill(metaObject: MetaObject) {
        log.info("Start update fill...");
        this.strictUpdateFill(metaObject, "updateUserId", Long::class.javaObjectType, 123456L)
        this.strictUpdateFill(metaObject, "updateTime", LocalDateTime::class.javaObjectType, LocalDateTime.now())
    }

}

3. Configure the Auto-fill Handler

Ensure your MyMetaObjectHandler class is managed by Spring, either through the @Component or @Bean annotation.

Notes

• Auto-fill directly sets values for the entity class properties.
• If a property has no value, it will be null when stored in the database.
• The default method strategy provided by MetaObjectHandler is: if a property has a value, it will not be overwritten; if the fill value is null, it will not be filled.
• Fields must be annotated with @TableField and the fill property must be set to specify the fill strategy.
• The fill handler must be declared as @Component or @Bean in Spring Boot.
• The strictInsertFill or strictUpdateFill methods can distinguish fill logic based on the FieldFill.xxx annotation, field name, and field type.
• If no distinction is needed, the fillStrategy method can be used.
• When using update(T entity, Wrapper<T> updateWrapper), entity cannot be null; otherwise, auto-fill will fail.
• When using update(Wrapper<T> updateWrapper), auto-fill will not occur, and field conditions must be manually assigned.

Parameter Fill Examples

// Insert fill example
insertFillByCustomMethod1(H2User h2User);
insertFillByCustomMethod8(H2User[] h2Users);
insertFillByCustomMethod4(Collection<H2User> h2User);

// Update fill example
updateFillByCustomMethod2(@Param("coll") Collection<Long> ids, @Param("et") H2User h2User);
updateFillByCustomMethod4(@Param("colls") Collection<Long> ids, @Param("et") H2User h2User);

Non-fillable Examples

// The method parameter name does not meet the fill condition. Replace "user" with "et" for correct filling.
updateFillByCustomMethod3(@Param("coll") Collection<Long> ids, @Param("user") H2User h2User);

FieldFill Enum

public enum FieldFill {
    DEFAULT,       // Default: no processing
    INSERT,        // Fill field on insertion
    UPDATE,        // Fill field on update
    INSERT_UPDATE  // Fill field on insertion and update
}

By following these steps, you can easily implement the auto-fill feature in MyBatis-Plus to improve development efficiency.