hibernate 使用@Data 注释创建的“没有实体的默认构造函数”

Question

I am trying to set up a database table using a JpaRepository. I have the following model class:

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

import lombok.Data;

@Data
@Entity
@Table
public class MyModel {
    @Id
    @GeneratedValue
    private final int id;
    private final String name;
    private final String imagePath;
}

When I run my application the table is created just fine. I have manually added a row to the table, yet when I try to look up the row using repository.findById I get the following error:

org.hibernate.InstantiationException: No default constructor for entity:  : com.mypackage.mypackage.model.MyModel

I am confused by the 'no default constructor' error. I thought the @Data annotation automatically created a constructor for the class?

Answer 1

Hibernates doesn't play with with immutable entities, it wants:

• a nullary constructor: public MyModel() {}
• getters and setters

So just remove the final modifiers so that @Data generates all this for you.

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Ah, that's why it rings a bell, it relates to that other question of yours . So yeah, with Hibernate entities, you can't easily use immutable entities. You can still add @AllArgsConstructor alongside @Data if you need such a constructor too.

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Edit: As rightfully raised by Andrey B. Panfilov in the comments, @Data shouldn't be used at all on top of entities. Quoting Thorben Janssen :

The bottom line is that you can use the @Getter , @Setter , and @Builder annotation without breaking your application. The only Lombok annotations you need to avoid are @Data , @ToString , and @EqualsAndHashCode .