Given an Enitiy Product
@Entity
public class Product {
private Long id;
private List<Review> reviews;
public Product() {}
@Id
@GeneratedValue
public Long getId() {
return this.id;
}
public void setId(Long id) {
this.id = id;
}
@ElementCollection
public List<Review> getReviews() {
return reviews;
}
public void setReviews(List<Review> reviews) {
this.reviews = reviews;
}
// equals() and hashCode() omitted for brevity
}
And an Embeddable Review
@Embeddable
public class Review {
private Customer author;
private String title;
private String comment;
public Review() {}
@ManyToOne(optional = false)
@Column(unique = true)
public Customer getAuthor() {
return author;
}
public void setAuthor(Customer author) {
this.author = author;
}
@Column(nullable = false)
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
@Column(nullable = false, length = 2000)
public String getComment() {
return comment;
}
public void setComment(String comment) {
this.comment = comment;
}
}
How can I set an unique constraint for the Review‘s author. In other words: I want to make sure, that for a given product each review has a different author.
Can I use @NaturalId? Do I use @Column(unique = true)? I already found a similar question on StackOverflow, but in my case it’s a list of Embeddables and not just a member, so that that approach won’t work, I guess.
Thanks a lot in advance!
Answer
If you are talking about having a unique database index added during schema generation then you can do this as below:
@ElementCollection
@CollectionTable(name = "product_reviews",
uniqueConstraints = {@UniqueConstraint(columnNames={"product_id", "author_id"})})
public List<Review> getReviews() {
return reviews;
}