Operation save in Grails on a POGO - grails

Question

I'm beginner in Grails and I have a problem when I try to save a POGO
I have created 1 domain class
class Book {
String title
}
Then, I have generated the controller and view automatically.
Now, I want to be able to create a book with the code by clicking "create" (I know it is possible directly with the code generated but for my example I want to do it by the code). To do this, I have modified the method 'save(Book bookInstance)' in the controller like this
#Transactional
def save(Book bookInstance) {
def book = new Book(title:"New Grails Book").save()
But, when I go to the URL localhost:8080/myApp/book/create and then I click "Create", I have the error
message -> /myApp/WEB-INF/grails-app/views/book/save.jsp
description -> The requested resource is not available.
When I put this code in bootStrap, it is OK, so I don't understand why it is not in the controller

Answer 1

When you have a hasMany property in a domain class, Grails adds a Set property to the domain class with an AST transformation (so it's actually there in the bytecode, and it's visiable to Java) to represent the collection, and when you add a belongsTo a field of that type is added. So it's as if you had this code:
class Author {
Set<Book> books
static hasMany = [books: Book]
String name
}
and
class Book {
Author author
static belongsTo = [author: Author]
String title
}
The AST xform uses the map key as the field name, so you can use any valid field name, but the convention is to do what you did.
Properties are nullable:false by default, so your code doesn't save the Book instance because you didn't set the author property. When doing this explicitly you typically don't create the Book directly, but instead add it to the Author's collection using the dynamic addToBooks method. This sets the author field back-reference and when you save the author, the book is transitively validated and saved. This is all handled for you when you have code like new Book(params).save(), and you can do it directly, e.g.
Author author = ...
def book = new Book(title:"New Grails Book", author: author).save()
If you're using a generated controller and GSPs, there should be an author id in the params map, it'll likely be author.id, so that first line would be
Author author = Author.get(params['author.id'])
but you can add
println params
at the top of the action method to see all of the submitted params.
In general you don't want to look at the return value of the save call, since it will be null if there's a validation error and there's no way to retrieve the errors. So change
def book = new Book(...).save()
to
def book = new Book(...)
book.save()
and now you can call book.hasErrors(), book.getErrors(), book.errors, etc. to see if it was successful and if not, what went wrong.
But that's not the exact problem you're seeing, just one you will when you fix your problem. There's no save.gsp, and Grails also looks for save.jsp and confusingly includes that name in the not-found message. The save method is accessed via a POST request, typically from the form generated by the create action, and it either re-displays create.gsp with the submitted data and error messages when validation fails, or redirects to the view action when the save succeeds. There's no need for a save.gsp when using the generated code.