Primary key violation when inserting child entity - spring

Question

DB Schema (H2 database):
create table book (
id_book bigint auto_increment not null primary key,
title varchar(255) not null,
id_author bigint not null,
id_genre bigint not null
);
create table comment (
id_comment bigint auto_increment not null primary key,
id_book bigint not null,
comment_text varchar(255) not null
);
Domain classes:
public class Book {
#Id
#Column("id_book")
private Long id;
private String title;
#Column("id_author")
AggregateReference<Author, Long> author;
#Column("id_genre")
AggregateReference<Genre, Long> genre;
#MappedCollection(idColumn = "id_book", keyColumn = "id_comment")
List<Comment> comments = new ArrayList<>();
public void addComment(String commentText) {
comments.add(new Comment(commentText));
}
//getters and setters
}
public class Comment {
#Column("id_comment")
private Long id;
#Column("comment_text")
private String text;
public Comment(String text) {
this.text = text;
}
public Comment() {
}
//getters and setters
}
I have the problem when I add a comment to the book.
```java
#Override
#Transactional
public String addComment(long bookId, String commentText) {
var book = bookRepository.findById(bookId);
return book.map(b -> {
b.addComment(commentText);
b = bookRepository.save(b);
return bookConverter.convertToString(b);
}).orElse("Book not found!");
}
It generates SQL like this...
Executing SQL batch update [INSERT INTO "COMMENT" ("comment_text", "id_book", "id_comment") VALUES (?, ?, ?)]
... adds values for id_comment field like 0, 1, 2, 3 and these values intersect with existing ones. So I get Primary Key Violation. Why it adds id_comment field to the INSERT expression?

Answer 1

Why it adds id_comment field to the INSERT expression?
Because you told it to.
The following annotation tells Spring Data JDBC to store the index of the list in the id_comment column.
#MappedCollection(idColumn = "id_book", keyColumn = "id_comment")
Your data model is missing a column for the list index. Add that column and use it as keyColumn in the #MappedCollection annotation