Question

Part of a web app I’m working on handles forms that need to be bound to a collection of model (case class) instances. See this question

So, if I were to add several users at one time, form fields would be named email[0], email[1], password[0], password[1], etc.

Posting the form results in a Map[String, Seq[String]]

Now, what I would like to do is to process the Map in batches, by index, so that for each iteration I can bind a User instance, creating a List[User] as the final result of the bindings.

The hacked approach I’m thinking of is to regex match against "[\d]" in the Map keys and then find the highest index via filter or count; with that, then (0..n).toList map{ ?? } through the number of form field rows, calling the binding/validation method (which also takes a Map[String, Seq[String]]) accordingly.

What is a concise way to achieve this?

Answer 1

Assuming that:

1. All map keys are in form "field[index]"
2. There is only one value in Seq for each key.
3. If there is entry for "email[x]" than there is entry for "password[x]" and vice versa.

I would done something like this:

val request = Map(
  "email[0]" -> Seq("[e-mail]"),
  "email[1]" -> Seq("[e-mail]"),
  "password[0]" -> Seq("%vT*n7#4"),
  "password[1]" -> Seq("Bfts7B&^")
)

case class User(email: String, password: String)

val Field = """(.+)\[(\d+)\]""".r

val userList = request.groupBy { case (Field(_, idx), _) => idx.toInt }
                      .mapValues { userMap =>
                          def extractField(name: String) =
                              userMap.collect{case (Field(`name`, _), values) => values.head}.head
                          User(extractField("email"), extractField("password"))}    
                      .toList.sortBy(_._1).map(_._2)

// Exiting paste mode, now interpreting.

request: scala.collection.immutable.Map[String,Seq[String]] = Map(email[0] -> List([e-mail]), 
email[1] -> List([e-mail]), password[0] -> List(%vT*n7#4), password[1] -> List(Bfts7B&^))
defined class User
Field: scala.util.matching.Regex = (.+)\[(\d+)\]
userList: List[User] = List(User([e-mail],%vT*n7#4), User([e-mail],Bfts7B&^))