Hibernate

Equal and Hash code

For hibernate to determine if two object are the same or not.

1. To ensure Hibernate can compare objects effectively, it’s common to define equals and hashCode methods for JPA entities. Hibernate uses these methods internally for object equality checks.

2. There are different strategies to implement equals and hashCode. Some use only the ID property, while others include all class properties. The choice depends on your specific use case.

3. In this example, we’ll focus on using the ID property. If two entities share the same ID, Hibernate will treat them as equal.

4. In IntelliJ:

   • Use Command + N (on Mac) to open the generation menu.
   • Select equals and hashCode.
   • Choose the IntelliJ default and deselect other properties, keeping only ID. Note: ID might initially be null when the object is created.

5. Here’s the generated code for the equals and hashCode methods. Repeat this for the Book entity as well.

6. Next, let’s add a toString method:

   • Again, use Command + N and select toString.
   • This method gives a readable string representation of the entity, showing its name and property values (almost like JSON but not quite).
   • Implement toString for both the Author and Book entities.

7. Once done, commit these changes to GitHub.

Summary:

• Implemented equals and hashCode using only the ID property.
• Added toString methods for better debugging and representation.
• This setup ensures Hibernate can efficiently manage entity comparisons based on your use case.