Populating the list in g.select - select

Question

I need to programmatically load a list.
Instead of:
<g:select
name="cars"
from="${Car.list()}"
value="${person?.cars*.id}"
optionKey="id"
multiple="true" />
I would like to do it this because, the list is not always coming from the same source
g.select(name : searchfield.fieldName,
class : "fillWidth searchfield",
multiple : "true",
from : ${ searchfield.fieldFrom },
optionKey : searchfield.fieldKey,
optionValue : searchfield.fieldValue)
The from does not load. with the list, I get an error message:
No signature of method: sample.SearchTagLib.$() is applicable for argument types: (sample.SearchTagLib$_getSelectField_closure5) values: [sample.SearchTagLib$_getSelectField_closure5#1187b50] Possible solutions: is(java.lang.Object), any(), use([Ljava.lang.Object;), any(groovy.lang.Closure), wait(), grep()

Answer 1

You don't need the ${} in the from option
g.select(name : searchfield.fieldName,
class : "fillWidth searchfield",
multiple : "true",
from : searchfield.fieldFrom,
optionKey : searchfield.fieldKey,
optionValue : searchfield.fieldValue)
In Groovy code ${} is a way to put Groovy expressions inside double quoted GStrings, if you're not in a GString you can just use the expression directly without wrapping it in ${}.
Edit from your comment
The fieldFrom at this point is a string which would get its value from a database. So the value in the DB is "Car.list()" which in the prototype I need to convert to a bound able or execute-able line of code.
It's not generally recommended to allow your app to execute arbitrary snippets of Groovy code provided by users (for obvious security reasons). As long as the code snippets come from a secure source such as a trusted admin user then fair enough, it is possible using GroovyShell
def from = new GroovyShell().evaluate(searchfield.fieldFrom)
but this is likely to be rather inefficient, creating a new classloader and parsing and compiling a whole Groovy script class every time. If the fieldFrom values are intended to always be pulling something from the database (i.e. they'll always be something like Car.list() or Vehicle.findAllByNumberOfWheelsGreaterThan(2), rather than arbitrary Groovy like [1,2,3]) then it might be better to store HQL expressions in fieldFrom and run them using executeQuery
def from = AnyDomainClass.executeQuery(searchfield.fieldFrom)
(executeQuery is a static GORM method, you need to call it on a specific domain class but it can return results of any type). The HQL equivalent of Car.list() would be "from Car", the equivalent of Vehicle.findAllByNumberOfWheelsGreaterThan(2) would be "from Vehicle where numberOfWheels > 2", etc.

Answer 2

I think you need to use strings as the attribute name:
g.select('name' : searchfield.fieldName,
'class' : "fillWidth searchfield",
'multiple' : "true",
'from' : ${ searchfield.fieldFrom },
'optionKey' : searchfield.fieldKey,
'optionValue' : searchfield.fieldValue)