What happens if I promote the column to be a/the PK, too (a.k.a. identifying relationship)? As the column is now the PK, I must tag it with @Id (…). This enhanced support of derived identifiers is actually part of the new stuff in JPA 2.0 (see the section 2.4.1 Primary Keys Corresponding to Derived Identities … Read more
The technical definition of an identifying relationship is that a child’s foreign key is part of its primary key. CREATE TABLE AuthoredBook ( author_id INT NOT NULL, book_id INT NOT NULL, PRIMARY KEY (author_id, book_id), FOREIGN KEY (author_id) REFERENCES Authors(author_id), FOREIGN KEY (book_id) REFERENCES Books(book_id) ); See? book_id is a foreign key, but it’s also … Read more
An identifying relationship is when the existence of a row in a child table depends on a row in a parent table. This may be confusing because it’s common practice these days to create a pseudokey for a child table, but not make the foreign key to the parent part of the child’s primary key. … Read more