Stupid doubt about Grails ORM

[Halley Thomas]

I was exploring Grails and I found this stupid stupid doubt!!!

Two classes

class Publisher {
    String pubName
    String address
}

class Book {
    String title
    String author
    String category

    static belongsTo = [pub : Publisher]

}

When I try to delete an object of Publisher, it is not letting me.
An exception is raised, org.hibernate.exception.ConstraintViolationException: could not delete: [libraryonline.Publisher#1].

Any explanations please?

[Gregg Bolinger]

There is no reason, given the code you provided, that the publisher should not be deleted. I used your code and wrote the following test, all passing:

void testDeletePublisher() {

    mockDomain(Book)
    mockDomain(Publisher)

    def pub1 = new Publisher(pubName: 'APress', address: 'Some Street')
    pub1.save(flush: true)
    assertNotNull("pub1 did not save", pub1.id)

    def book1 = new Book(title: 'Definative Guide to Grails', author: 'John Doe', category: 'Grails', pub: pub1)
    book1.save(flush: true)
    assertNotNull('book1 did not save', book1)

    def pubToDelete = Publisher.findByPubName('APress')
    assertNotNull('could not find publisher APress', pubToDelete)
    pubToDelete.delete(flush: true)

    pubToDelete = Publisher.findByPubName('APress')
    assertNull('APress did not delete', pubToDelete)
}

Maybe you have left something out that needs to be shared so we see more of what is going on. Maybe show us the code where you are deleting?

[Halley Thomas]

I am using the defaul scaffolding of Grails. I haven't written any code for that!!

[Gregg Bolinger]

Halley Thomas wrote:I am using the defaul scaffolding of Grails. I haven't written any code for that!!

Domains aren't scaffolded so your point makes no sense. Write a unit test and see what your results are. In fact, you could just copy and paste the one I wrote for you if the domains are the same.

[chris webster]

My guess is that it is failing because your Publisher still has Books belonging to it, so it is causing a foreign key constraint error in your database. That's what constraints are for - to stop you doing bad things by mistake .

In general, you need to make sure that deleting the Publisher cascades to the Books if you want them to be deleted at the same time. Maybe the problem is that your Publisher class does not know it has Books (although it should know this from the belongsTo declaration), so it does not know it has to delete them as well. Not sure why this would be the case, but you could try adding this to your Publisher class so it knows explicitly that it has Books:

static hasMany = [books:Book]

[Gregg Bolinger]

chris webster wrote:My guess is that it is failing because your Publisher still has Books belonging to it, so it is causing a foreign key constraint error in your database. That's what constraints are for - to stop you doing bad things by mistake .

You need to make sure that deleting the Publisher cascades to the Books if you want them to be deleted at the same time.

If his code is what he posted, Publisher does not belong to a Book. He has no belongsTo in his code. So that shouldn't be the issue.

[chris webster]

Gregg Bolinger wrote:
If his code is what he posted, Publisher does not belong to a Book. He has no belongsTo in his code. So that shouldn't be the issue.

No, but the Publisher implicitly "hasMany" books, because he does say explicitly that a Book "belongsTo" a Publisher, so right now it looks like Grails is leaving them there in the database when it tries to delete the Publisher.

But that's just my guess...

[Halley Thomas]

Yup. It worked Chris. Thanks.
I guess you have to map explicitly.
Is it just GORM?
I need to try the same in JPA and see the outcome..