Search implementation for a RESTful interface on Grails - rest

Question

I'm building a RESTful interface on a Grails 2.1.1 application. How should I implement search operations? I don't want to repeat huge amounts of code, which my current thinking would require.
The server structure is quite normal Grails-MVC: domain classes represent data, controllers offer the interface and services have the business logic. I use command objects for data binding in controllers but not on service methods. The client is a web UI. My goal is to have search URLs like this:
/cars/?q=generic+query+from+all+fields
/cars/?color=red&year=2011
(I'm aware of the debate on the RESTfulness of this kind of URLs with query strings: RESTful URL design for search. While I think this is the best model for my purpose, I'm open to alternatives if they make the API and the implementation better.)
As you can see from the code examples below my problem is with the second kind of URL, the field-specific search. In order to implement this kind of search operation for several domain classes with lots of fields my method signatures would explode.
There probably is a "Groovy way" to do this but I'm still a bit of a n00b in finer Groovy tricks :)
Domain:
class Car {
String color
int year
}
Controller:
class CarsController {
def carService
def list(ListCommand cmd) {
def result
if (cmd.q) {
result = carService.search(cmd.q, cmd.max, cmd.offset, cmd.order, cmd.sort)
}
else {
result = carService.search(cmd.color, cmd.year, cmd.max, cmd.offset, cmd.order, cmd.sort)
}
render result as JSON
}
class ListCommand {
Integer max
Integer offset
String order
String sort
String q
String color // I don't want this field in command
int year // I don't want this field in command
static constraints = {
// all nullable
}
}
// show(), save(), update(), delete() and their commands clipped
}
Service:
class CarService {
List<Car> search(q, max=10, offset=0, order="asc", sort="id") {
// ...
}
List<Car> search(color, year, max=10, offset=0, order="asc", sort="id") {
// ...
}
}
UrlMappings:
class UrlMappings {
static mappings = {
name restEntityList: "/$controller"(parseRequest: true) {
action = [GET: "list", POST: "save"]
}
name restEntity: "/$controller/$id"(parseRequest: true) {
action = [GET: "show", PUT: "update", POST: "update", DELETE: "delete"]
}
}
}

Answer 1

You can get all this parameters from params, like:
result = carService.search(params.color, params.year as Integer, cmd.max, cmd.offset, cmd.order, cmd.sort)
All values of params map are strings, so you should convert it to appropriate data structures in controller (and it's better to check that params.year is actual number)
Update
If you don't want to writer field names, you can pass it as a Map:
resutl = carService.search(params)
where
List<Car> search(Map params)