iterate over case class data members

Question

I am writing a play2.1 application with mongodb, and my model object is a bit extensive. when updating an entry in the DB, i need to compare the temp object coming from the form with what's in the DB, so i can build the update query (and log the changes).

i am looking for a way to generically take 2 instances and get a diff of them. iterating over each data member is long, hard-coded and error prone (if a.firstName.equalsIgnoreCase(b.firstName)) so i am looking for a way to iterate over all data members and compare them horizontally (a map of name -> value will do, or a list i can trust to enumerate the data members in the same order every time).

any ideas?

case class Customer(
  id: Option[BSONObjectID] = Some(BSONObjectID.generate),
  firstName: String,
  middleName: String,
  lastName: String,
  address: List[Address],
  phoneNumbers: List[PhoneNumber],
  email: String,
  creationTime: Option[DateTime] = Some(DateTime.now()),
  lastUpdateTime: Option[DateTime] = Some(DateTime.now())
)

all three solutions below are great, but i still cannot get the field's name, right? that means i can log the change, but not what field it affected...

Answer 1

Maybe productIterator is what you wanted:

scala> case class C(x: Int, y: String, z: Char)
defined class C

scala> val c1 = C(1, "2", 'c')
c1: C = C(1,2,c)

scala> c1.productIterator.toList
res1: List[Any] = List(1, 2, c)

Answer 2

Expanding on @Malte_Schwerhoff's answer, you could potentially create a recursive diff method that not only generated the indexes of differences, but mapped them to the new value at that index - or in the case of nested Product types, a map of the sub-Product differences:

def diff(orig: Product, update: Product): Map[Int, Any] = {
  assert(orig != null && update != null, "Both products must be non-null")
  assert(orig.getClass == update.getClass, "Both products must be of the same class")

  val diffs = for (ix <- 0 until orig.productArity) yield {
    (orig.productElement(ix), update.productElement(ix)) match {
      case (s1: String, s2: String) if (!s1.equalsIgnoreCase(s2)) => Some((ix -> s2))
      case (s1: String, s2: String) => None
      case (p1: Product, p2: Product) if (p1 != p2) => Some((ix -> diff(p1, p2)))
      case (x, y) if (x != y) => Some((ix -> y))
      case _ => None
    }
  }

  diffs.flatten.toMap
}

Expanding on the use cases from that answer:

case class A(x: Int, y: String)
case class B(a: A, b: AnyRef, c: Any)

val a1 = A(4, "four")
val a2 = A(4, "Four")
val a3 = A(4, "quatre")
val a4 = A(5, "five")
val b1 = B(a1, null, 6)
val b2 = B(a1, null, 7)
val b3 = B(a2, a2, a2)
val b4 = B(a4, null, 8)

println(diff(a1, a2)) // Map()
println(diff(a1, a3)) // Map(0 -> 5)
println(diff(a1, a4)) // Map(0 -> 5, 1 -> five)

println(diff(b1, b2)) // Map(2 -> 7)
println(diff(b1, b3)) // Map(1 -> A(4,four), 2 -> A(4,four))
println(diff(b1, b4)) // Map(0 -> Map(0 -> 5, 1 -> five), 2 -> 8l

Answer 3

You can use the product iterator, and match on the elements if you want to use non-standard equality such as String.equalsIgnoreCase.

def compare(p1: Product, p2: Product): List[Int] = {
  assert(p1 != null && p2 != null, "Both products must be non-null")
  assert(p1.getClass == p2.getClass, "Both products must be of the same class")

  var idx = List[Int]()

  for (i <- 0 until p1.productArity) {
    val equal = (p1.productElement(i), p2.productElement(i)) match {
      case (s1: String, s2: String) => s1.equalsIgnoreCase(s2)
      case (x, y) => x == y
    }

    if (!equal) idx ::= i
  }

  idx.reverse
}

Use cases:

case class A(x: Int, y: String)
case class B(a: A, b: AnyRef, c: Any)

val a1 = A(4, "four")
val a2 = A(4, "Four")
val a3 = A(5, "five")
val b1 = B(a1, null, 6)
val b2 = B(a1, null, 7)
val b3 = B(a2, a2, a2)

println(compare(a1, a2)) // List()
println(compare(a1, a3)) // List(0, 1)

println(compare(b1, b2)) // List(2)
println(compare(b2, b3)) // List(0, 1, 2)

// println(compare(a1, b1)) // assertion failed