Auto-Fill Fields

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

Overview

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

Usage Steps

1. Define the Entity Class

In your 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("Starting 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("Starting 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: When converting Kotlin types to Java types, use xxx::class.javaObjectType to prevent type mismatches that may occur if xxx::class.java converts to primitive types, which would cause auto-fill to fail.
    override fun insertFill(metaObject: MetaObject) {
        log.info("Starting 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("Starting 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, which can be achieved using the @Component or @Bean annotation.

Important Notes

Auto-fill directly sets values on 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, no filling will occur.
Fields must be declared with the @TableField annotation, and the fill attribute must be set to specify the fill strategy.
The fill handler must be declared as a @Component or @Bean in Spring Boot.
Use the strictInsertFill or strictUpdateFill methods to differentiate fill logic based on the FieldFill.xxx annotation, field name, and field type.
If differentiation is not needed, you can use the fillStrategy method.
When using update(T entity, Wrapper<T> updateWrapper), the entity cannot be null, otherwise auto-fill will not work.
Auto-fill does not occur when using update(Wrapper<T> updateWrapper); you must manually assign values to field conditions.

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);

Failed Fill Example

// The method parameter name does not meet the fill condition. Change 'user' to '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 insert
    UPDATE,        // Fill field on update
    INSERT_UPDATE  // Fill field on insert and update
}

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

Power by Astro Starlight | Sponsored by JetBrains