Grails: How to insert with many-to-many with extra column? - grails

Question

Take the example of author, book and with a join table author_books with an extra royalty column:
CREATE TABLE 'author_books' (
'author_id` bigint(20) NOT NULL,
'book_id' bigint(20) NOT NULL,
'royalty' int NOT NULL,
PRIMARY KEY ('author_id', 'book_id') ,
INDEX 'FK24C812F6183CFE1B' ('book_id'),
INDEX 'FK24C812F6DAE0A69B' ('author_id')
)
If I don't have the db-reverse-engineer plugin generate the AuthorBooks class, the generated code would be:
class Author {
String name
static hasMany = [books: Book]
}
class Book {
String title
static hasMany = [authors: Author]
static belongsTo = [Author]
}
The following code:
def author1 = new Author(name: 'author1').addToBooks(new Book(title:
'book1')).save(flush: true)
would insert one row into author table and one row in book table, but would fail to insert into author_books because royalty cannot be null.
However if have the db-reverse-engineer plugin generate the AuthorBooks class, the generated code would be:
class Author {
String name
static hasMany = [authorBookses: AuthorBooks]
}
class Book {
String title
static hasMany = [authorBookses: AuthorBooks]
}
class AuthorBooks implements Serializable {
Long authorId
Long bookId
Integer royalty
Author author
Book book
int hashCode() {
def builder = new HashCodeBuilder()
builder.append authorId
builder.append bookId
builder.toHashCode()
}
boolean equals(other) {
if (other == null) return false
def builder = new EqualsBuilder()
builder.append authorId, other.authorId
builder.append bookId, other.bookId
builder.isEquals()
}
static belongsTo = [author: Author, book: Book]
static mapping = {
author insertable: false // these insertable and updateable codes were manually added
author updateable: false // otherwise it would not run
book insertable: false
book updateable: false
id composite: ["authorId", "bookId"]
version false
}
}
In this case, I cannot call author.addToAuthorBooks(new AuthorBooks( )) because author_books cannot have author_id or book_id to be null. In the end I need to do the following to get it work:
def author1 = new Author(name: 'author1').save(flush: true)
def book1 = new Book(title: 'book1').save(flush: true)
def authorbook1 = new AuthorBooks(authorId: author1.id, bookId: book1.id,
royalty: 50, author: author1, book: book1).save(flush: true)
which is acceptable to me. But then what is the benefits of having hasMany association in the Author and Book class? Any better way to do this? Ideally, something like following would be cool
def author1 = new Author(name: 'author1').addToBooks(book: new Book(title: 'book1'),
royalty: 50).save(flush: true)

Answer 1

There are some changes that I would like to recommend,specifically in your AuthorBooks domain:
class Author {
String name
static hasMany = [authorBookses: AuthorBooks]
}
class Book {
String title
static hasMany = [authorBookses: AuthorBooks]
}
class AuthorBooks implements Serializable {
Integer royalty
Author author
Book book
int hashCode() {
def builder = new HashCodeBuilder()
builder.append author.id
builder.append book.id
builder.toHashCode()
}
boolean equals(other) {
if (other == null) return false
def builder = new EqualsBuilder()
builder.append author.id, other.author.id
builder.append book.id, other.book.id
builder.isEquals()
}
static belongsTo = [author: Author, book: Book]
static mapping = {
id composite: ["author", "book"]
version false
}
}
Having additional ids for book and author is redundant. I'm not 100% sure about what I'm going to suggest, but it would be worth of trying the following:
def author1 = new Author(name: 'author1', authorBookses: new HashSet())
def book1 = new Book(title: 'book1', authorBookses: new HashSet())
def authorbook1 = new AuthorBooks(royalty: 50, author: author1, book: book1)
author1.authorBookses(authorbook1)
book1.authorBookses(authorbook1)
authorbook1.save(flush: true)