https://github.com/shofiq0023/spring-data-jpa-demo

This is a simple demo project using Spring Data JPA for demonstrating data relations and features of JPA
https://github.com/shofiq0023/spring-data-jpa-demo

data-jpa database database-relationships java spring-boot

Last synced: about 19 hours ago
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This is a simple demo project using Spring Data JPA for demonstrating data relations and features of JPA

• Host: GitHub
• URL: https://github.com/shofiq0023/spring-data-jpa-demo
• Owner: shofiq0023
• Created: 2023-09-21T17:22:24.000Z (about 1 year ago)
• Default Branch: master
• Last Pushed: 2023-10-31T15:53:34.000Z (about 1 year ago)
• Last Synced: 2024-03-20T22:20:52.145Z (8 months ago)
• Topics: data-jpa, database, database-relationships, java, spring-boot
• Language: Java
• Homepage:
• Size: 89.8 KB
• Stars: 0
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
# Data relation with JPA mapping

This is a demonstration project for data mapping with Spring data JPA.

### Some pointers of this project:

- There is no authentication in this project as this is a demo project.

- This project demonstrate the JPA Mapping like One-to-One, Many-to-One, Many-to-Many mapping.

# One-to-One Mapping:

This mapping is where one entity with directly related with exactly one another entity. This is demonstrated by the **User** and **UserPersonalInfo** entity in the project.  

In the **User** entity the **@OneToOne** annotation is used for the mapping. Cascade type is set to **ALL** for reflecting any changes made to the **User** entity.

```java

// Entity class

public class User {

	// Other properties

	@OneToOne(cascade = CascadeType.ALL)

	@JoinColumn(name = "personal_info_id", referencedColumn = "id")

	private UserPersonalInfo personalInfo;

	// Getters and setters

}

```

**@JoinColumn** annotation is used on the owning side of the relation. In My case **User** is the owning side. **@JoinColumn** is not necessary but for controll I included the annotation. This annotation defines the relation by using the other entity's "id".  

  

On the other hand, for the **UserPersonalInfo** entity, I added the **@OneToOne** and **@JsonBackReference** annotation.

```java

// Entity class

public class UserPersonalInfo {

	// Other properties

	@OneToOne(mappedBy = "personalInfo")

	@JsonBackReference

	private User user;

	// Getters and setters

}

```

Here the **@JsonBackReference** was used to avoid **Jackson data bind loop error**. This annotation is required if you want to return the entity class in response. I would suggest using a DTO for API response. I returned the entity class for the sake of this demonstration.

# One-to-Many Mapping:

This mapping is where one entity is related to multiple other entities. This is the most commonly used relationship. This is demonstrated by the **Book** and **Author** entity in this project.  

In this case the Book is the owning side of this relationship.  

```java

// Entity class

public class Book {

	@ManyToOne

	@JoinColumn(name = "author_id")

	@JsonBackReference

	private Author author;

}

// Entity class

public class Author {

	@OneToMany(mappedBy = "author", cascade = CascadeType.ALL, orphanRemoval = true)

	private List books;

}

```

Here the relationship is Unidirectional as we have specified the owning and reverse side of the relationship.