How to handle optional query parameters in Play framework - scala

Question

Lets say I have an already functioning Play 2.0 framework based application in Scala that serves a URL such as:
http://localhost:9000/birthdays
which responds with a listing of all known birthdays
I now want to enhance this by adding the ability to restrict results with optional "from" (date) and "to" request params such as
http://localhost:9000/birthdays?from=20120131&to=20120229
(dates here interpreted as yyyyMMdd)
My question is how to handle the request param binding and interpretation in Play 2.0 with Scala, especially given that both of these params should be optional.
Should these parameters be somehow expressed in the "routes" specification? Alternatively, should the responding Controller method pick apart the params from the request object somehow? Is there another way to do this?

Answer 1

Encode your optional parameters as Option[String] (or Option[java.util.Date], but you’ll have to implement your own QueryStringBindable[Date]):
def birthdays(from: Option[String], to: Option[String]) = Action {
// …
}
And declare the following route:
GET /birthday controllers.Application.birthday(from: Option[String], to: Option[String])

Answer 2

A maybe less clean way of doing this for java users is setting defaults:
GET /users controllers.Application.users(max:java.lang.Integer ?= 50, page:java.lang.Integer ?= 0)
And in the controller
public static Result users(Integer max, Integer page) {...}
One more problem, you'll have to repeat the defaults whenever you link to your page in the template
#routes.Application.users(max = 50, page = 0)

Answer 3

In Addition to Julien's answer. If you don't want to include it in the routes file.
You can get this attribute in the controller method using RequestHeader
String from = request().getQueryString("from");
String to = request().getQueryString("to");
This will give you the desired request parameters, plus keep your routes file clean.

Answer 4

Here's Julien's example rewritten in java, using F.Option: (works as of play 2.1)
import play.libs.F.Option;
public static Result birthdays(Option<String> from, Option<String> to) {
// …
}
Route:
GET /birthday controllers.Application.birthday(from: play.libs.F.Option[String], to: play.libs.F.Option[String])
You can also just pick arbitrary query parameters out as strings (you have to do the type conversion yourself):
public static Result birthdays(Option<String> from, Option<String> to) {
String blarg = request().getQueryString("blarg"); // null if not in URL
// …
}

Answer 5

For optional Query parameters, you can do it this way
In routes file, declare API
GET /birthdays controllers.Application.method(from: Long, to: Long)
You can also give some default value, in case API doesn't contain these query params it will automatically assign the default values to these params
GET /birthdays controllers.Application.method(from: Long ?= 0, to: Long ?= 10)
In method written inside controller Application these params will have value null if no default values assigned else default values.

Answer 6

My way of doing this involves using a custom QueryStringBindable. This way I express parameters in routes as:
GET /birthdays/ controllers.Birthdays.getBirthdays(period: util.Period)
The code for Period looks like this.
public class Period implements QueryStringBindable<Period> {
public static final String PATTERN = "dd.MM.yyyy";
public Date start;
public Date end;
#Override
public F.Option<Period> bind(String key, Map<String, String[]> data) {
SimpleDateFormat sdf = new SimpleDateFormat(PATTERN);
try {
start = data.containsKey("startDate")?sdf.parse(data.get("startDate") [0]):null;
end = data.containsKey("endDate")?sdf.parse(data.get("endDate")[0]):null;
} catch (ParseException ignored) {
return F.Option.None();
}
return F.Option.Some(this);
}
#Override
public String unbind(String key) {
SimpleDateFormat sdf = new SimpleDateFormat(PATTERN);
return "startDate=" + sdf.format(start) + "&" + "endDate=" + sdf.format(end);
}
#Override
public String javascriptUnbind() {
return null;
}
public void applyDateFilter(ExpressionList el) {
if (this.start != null)
el.ge("eventDate", this.start);
if (this.end != null)
el.le("eventDate", new DateTime(this.end.getTime()).plusDays(1).toDate());
}
}
applyDateFilter is just a convienence method i use in my controllers if I want to apply date filtering to the query. Obviously you could use other date defaults here, or use some other default than null for start and end date in the bind method.