Grails 2.4.4 upgrade data binding issue - grails

Question

A pattern we use here for large dynamic forms is to allow the client to edit pretty much the entire graph including children and removal and addition of children is handled in javascript. Failing use case is when user deletes a property of one of the children and for this example we'll say the email address of the second child is removed and the parm is sent empty.
Example Class Structure
Domain X
Long id
String name
SortedSet<Child> children
Domain Child
Long id
Integer position // used to sort
String name (required)
String email (required)
Parms are named in this manner:
x.id = 1
x.name = 'blah'
x.children[0].id = 1
x.children[0].position = 0
x.children[0].name = 'childa0'
x.children[0].email = 'child0#any.com'
x.children[1].id = 2
x.children[1].position = 1
x.children[1].name = 'child1'
x.children[1].email = ''
Current stored values:
x.id = 1
x.name = 'blah'
x.children[0].id = 1
x.children[0].position = 0
x.children[0].name = 'childa0'
x.children[0].email = 'child0#any.com'
x.children[1].id = 2
x.children[1].position = 1
x.children[1].name = 'child1'
x.children[1].email = 'child1#any.com'
The pattern to update has been:
Browser
user edits all and submits changes
parms are sent as shown above and in this use case user accidentally deleted email address that is required (yes submit could be prevented in this simple case but there are more extensive validation rules and this is just a simple example to illustrate issue)
Server
retrieve current parent domain class using id parm
check current stored version against edited version and ensure it has not changed
apply all parms to current domain object in this manner: x.properties = parms.x
This is where it breaks down. With Grails 2.2.2 the email property of child[1] is updated to an empty string and running validation catches the error. Grails 2.4.4 does NOT update the child value. I know the data binding changed and perhaps there are valid reasons for this change but I can't fathom it. This has worked from 1.3.6 to 2.2.2.
One thing to note is that if I do not retrieve the domain class and instead create a new instance with the parms passed in all of the child parms are set correctly.
X x = new X(params.x)
This seems to indicate some Grails issue as the user guide talks about both methods as equal - one to use for new instances and the other for updates but the examples clearly demonstrate that both methods should handle indexed child properties.
Any help or thoughts are appreciated!

Answer 1

I ran into this problem my self upgrading an application from 2.2.4 to 2.4.4.
Setting grails.databinding.useSpringBinder = true for config.groovy
and adding grails-web-databinding-spring to the pom worked flawlessy for me.
Obviously doing this was a lot less hassle than rewriting all the binding code :-)

Answer 2

Looking into this further Grails 2.4.4 documentation states that it will bind sets positionally if they are indexed (ie. [0]).
http://grails.org/doc/latest/guide/single.html#dataBinding
The section titled "Data Binding and Many-ended Associations" states that these parms will be bound and that new instances of the set will be created if their index is greater than the current set. This was true for me in Grails 2.2.2 but NOT in 2.4.4.
HOWEVER, earlier in the documentation in the section "Binding To Collections And Maps" it states clearly: "When updating existing elements in a Set the Map being assigned to the Set must have id elements in it which represent the element in the Set".
If you are upgrading to Grails 2.4.4 and have any complex form data binding I suggest you look there first to decide whether to upgrade. Due to these changes in data binding this has become the most complex upgrade we've encountered yet with Grails.
The other disappointment with 2.4.4 is that it states you can override the new binding and fall back to the old spring binding but you cannot past 2.4 - at least from what I can gather from others' posts and my attempts. Setting the config property as documented and adding the dependency required resulted in startup runtime errors.

Answer 3

Apparently older versions of grails prior to 2.4.4 would match the child instances to params positionally, i.e. using the indexes ([0],[1], etc.) to match the children not caring if the IDs of the instances matched. The new binder does want the IDs of the instances to match before binding. I had never realised I was not placing the ID in a hidden field as it always worked perfectly.

Answer 4

I had a similar problem after migrating to Grails 2.4.4 (from 2.2.2). After a lot of reading and seaching (you must to definitly read http://docs.grails.org/2.4.4/guide/single.html#dataBinding mencioned in user2863513 post) I've resolved it in a very simple way
In my application I had nested domains relationships. Example:
class A {
String name
static hasMany = [b:B]
}
class B {
String name
static hasMany = [c:C]
}
class C {
String name
}
Due to the form complexity, class C object were not binding correcly. I've resolved this defining the C atribute on class B as a List (remember, has many relationships are implemented as Sets by default). So, my class B changed to:
class B {
String name
static hasMany = [c:C]
List c
}
And voila! Everything works perfectly again.