https://github.com/jetbrains/jpa-buddy-kotlin-entities

This repository shows how to declare Hibernate entities using Kotlin
https://github.com/jetbrains/jpa-buddy-kotlin-entities

hibernate jpa jpa-buddy jpa-entities kotlin sample

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This repository shows how to declare Hibernate entities using Kotlin

• Host: GitHub
• URL: https://github.com/jetbrains/jpa-buddy-kotlin-entities
• Owner: JetBrains
• License: apache-2.0
• Created: 2021-05-20T13:45:33.000Z (over 3 years ago)
• Default Branch: main
• Last Pushed: 2024-03-06T16:46:42.000Z (11 months ago)
• Last Synced: 2025-01-30T02:01:43.011Z (15 days ago)
• Topics: hibernate, jpa, jpa-buddy, jpa-entities, kotlin, sample
• Language: Kotlin
• Homepage:
• Size: 54.7 KB
• Stars: 64
• Watchers: 6
• Forks: 19
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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# JPA Entities in Kotlin

This repository was originally used in the "[Getting the Most from JPA with Kotlin](https://www.youtube.com/watch?v=a_6V8xwiv04)" webinar.

To follow the webinar flow step by step, checkout the "[webinar-starting-point](https://github.com/jpa-buddy/kotlin-entities/tree/webinar-starting-point)" branch and click on the image below to start watching.

[![Watch the video](https://img.youtube.com/vi/a_6V8xwiv04/hqdefault.jpg)](https://www.youtube.com/watch?v=a_6V8xwiv04)

## JPA Entities on Kotlin Checklist

- To avoid significant performace issues and enable lazy loading for _Many/One to One_ assosiations make sure you mark all JPA-related classes and their properties as `open`.

```

@Table(name = "project")

@Entity

open class Project {

    @Id

    @GeneratedValue(strategy = GenerationType.IDENTITY)

    @Column(name = "id", nullable = false)

    open var id: Long? = null

    @Column(name = "name", nullable = false)

    open var name: String? = null

    ...

}

```

- You may use the [*all-open*](https://kotlinlang.org/docs/all-open-plugin.html) compiler plugin to make all JPA-related classes and properties `open` by default. Make sure you configure it right, so it applys for all classes annotated as `@Entity`, `@MappedSuperclass`, `@Embeddable`. 

```

   ...

   all-open

   ...

   all-open:annotation=javax.persistence.Entity

   all-open:annotation=javax.persistence.MappedSuperclass

   all-open:annotation=javax.persistence.Embeddable

 

```

- Using primary constructors in JPA-related classes will cause the following exception `org.hibernate.InstantiationException: No default constructor for entity`. To resolve this issue you may manually define no-args constructor or use the [*kotlin-jpa*](https://kotlinlang.org/docs/no-arg-plugin.html#jpa-support) compiler plugin, which ensures that no-args constructor will be generated in bytecode for each JPA-related class.

```

   ...

   jpa

   ...   

```

-  To use data classes 

   * Enable the all-open plugin as it was described above, because this is the only way to make data classes `open` in the compiled bytecode.

   * Override `equals()`, `hashCode()`, `toString()` in accordance with one of this articles by [Vlad Mihalcea](https://vladmihalcea.com/the-best-way-to-implement-equals-hashcode-and-tostring-with-jpa-and-hibernate/) or [Thorben Janssen](https://thorben-janssen.com/ultimate-guide-to-implementing-equals-and-hashcode-with-hibernate/).

- [JPA Buddy](https://plugins.jetbrains.com/plugin/15075-jpa-buddy) is aware of all these things and always generate valid entities for you, including extra stuff like `equals()`, `hashCode()`, `toString()`!

Find more examples of JPA entities on Kotlin in the [domain.kt](src/main/kotlin/com/jpabuddy/kotlinentities/domain.kt) file. It also includes detailed explanation of the different use cases inlined in the comments.