Exception: Caused by: org.hibernate.AnnotationException: No identifier specified for entity

The error message ” org.hibernate.AnnotationException: No identifier specified for entity“, suggests that there is an issue with the entity mapping in your Hibernate configuration. Specifically, it indicates that Hibernate cannot find an identifier (primary key) for the entity. Here are a few potential causes:

1. Missing Primary Key Annotation: Ensure that the entity class has a primary key annotated with @Id.
2. Incorrect Mapping: Check if the primary key property is correctly mapped in the Hibernate configuration. Ensure that the @Id annotation corresponds to the primary key column in your database schema.
3. Inheritance Mapping Issue: If entity is part of an inheritance hierarchy, ensure that the appropriate inheritance strategy (@Inheritance) is applied and that the primary key is properly defined in the superclass or subclass.
4. Database Schema Issue: Double-check that the database schema matches the entity mapping. Make sure that there is a corresponding primary key column in the table mapped to the entity.
5. Mapping Annotations: Ensure that you’re using the correct annotations for entity mapping (e.g., @Entity, @Table, @Column) and that they are applied appropriately to your entity class and properties.

Let’s consider an example where we have an entity called HistoryDetails that represents user history. We’ll ensure that it has a primary key annotated properly:

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

@Entity
public class HistoryDetails {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id; // Primary Key

    private String userName;
    private LocalDateTime checkInTime;
    // Other fields and methods
}