a list of checkboxes - grails

Question

I have two domain classes
class Contract {
String number
static hasMany = [statements:Statement]
}
class Statement {
String code
static hasMany = [contracts:Contract]
}
I would like to show all statements available in my gsp with a checkbox next to each, allowing the user to choose which statements are applicable to the contract. So something like:
[ ] Statement Code 1
[ ] Statement Code 2
[ ] Statement Code 3
I started off with this:
<g:each in="${Statement.list()}" var="statement" status="i">
<g:checkBox name="statements[${i}].id" value="${statement.id}" checked="${contractInstance.statements.contains(statement.id)}" />
<label for="statements[${i}]">${statement.code}</label>
</g:each>
But i just cannot get a list of checked statements to the controller (there are null elements in the list, there are repeated statements...).
Any idea how to achieve this?

Answer 1

This is possible, but it does require a bit of a hack. First off, every checkbox must have the same name, "statements":
<g:each in="${org.example.Statement.list(sort: 'id', order: 'asc')}" var="statement" status="i">
<g:checkBox name="statements" value="${statement.id}" checked="${contract.statements.contains(statement)}" />
<label for="statements">${statement.content}</label>
</g:each>
Second, in the controller you have to remove the "_statements" property before binding:
def contract = Contract.get(params.id)
params.remove "_statements"
bindData contract, params
contract.save(failOnError: true)
The check box support hasn't been designed for this use case, hence the need for a hack. The multi-select list box is the one typically used for this type of scenario.

Answer 2

I personally prefer to get the list of Id's in this case.
<g:each var="book" in="${books}">
<g:checkBox name="bookIds" value="${book.id}" ...
</g:each>
Command Object:
class BookCommand {
List<Serializable> bookIds
}
In controller action:
BookCommand bc ->
author.books = Book.getAll(bc.bookIds)

Answer 3

Change the checkbox to something like this.
<g:checkBox name="statements.${statement.id}" value="true" checked="${contractInstance.statements.contains(statement)?:''}" />
and then in the controller, in params.statements you will get a list with the IDs of the checked statements.
Also notice the ?:'' in the checked property, it's a good idea to add it because any value(even 'false') in the checked property is interpreted as checked.

Answer 4

Are you mapping request directly to Contract? It's much more secure to map incoming request into an Command object.
As about mapping a list - values are mapped only to existing elements. I mean it cannot create new list elements. You need to prepare it before mapping. If you know that there is always 3 elements, you can make:
class ContractCommand {
List statements = [
new Statement(),
new Statement(),
new Statement(),
]
}
and map request to this object