Spring Data JPA Relationship Annotations

Question

I'm learning Spring Data JPA and having some trouble establishing the relationship between these two tables:

product table with columns id, name, product_type_id
product_type table with columns id, name

A product can have only one type. A type can be associated with many products.

Where would I use the @OnetoMany and @ManytoOne annotations in my entity classes?

Read basic JPA (nothing to do with Spring) documentation. http://www.datanucleus.org/products/accessplatform_5_1/jpa/mapping.html#one_many_relations — Neil Stockton, Jun 08 '17 at 07:29

cassiomolin · Accepted Answer · 2017-06-08T07:28:04.753

For the situation you mentioned in your question, your entities should be like:

@Entity
public class Product {

    @Id
    @GeneratedValue
    private Long id;

    private String name;

    @ManyToOne
    private ProductType type;

    // Getters and setters
}

@Entity
public class ProductType {

    @Id
    @GeneratedValue
    private Long id;

    private String name;

    @OneToMany(mappedBy = "type")
    private List<Product> products;

    // Getters and setters
}

score 0 · Answer 2 · answered Jun 07 '17 at 21:47

0

Entity Product should have field ProductType with annotation @ManyToOne. Entity ProductType should have field Set with annotation @OneToMany(mappedBy = 'productType')

answered Jun 07 '17 at 21:47

Vitalii Kravchenko

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score 0 · Answer 3 · answered Jun 08 '17 at 01:31

Cassio Mazzochi Molin's answer should work for you after correcting the little mistake he made in the inverse entity (I.e. ProductType class). The @OneToMany should be mapped to the variable type in the owning entity (i.e. Product class) and not productType. So that line should be

@OneToMany(mappedBy = "type")

I will also suggest you pick up a good tutorial book on jpa 2 and study, specially the relationship part because there's lot of rules to it which you can only learn by studying on your own else you will keep asking questions here, trust me.

Pro JPA 2 : Mastering the JAVA persistence API by Apress is a very nice tutorial book that can help you.

Spring Data JPA Relationship Annotations

3 Answers3