Scala Slick Bulk Insert with Array

Question

I'm splitting a long string into an array of strings, then I want to insert all of them to the database. I can easily loop through the array and insert one by one, but it seems very inefficient. Then I think there is a insertAll() method. However, the insertAll() method is defined like this:

def insertAll(values: U*)

This only accepts multiple U, but not an Array or List.

/* Insert a new Tag  */
def insert(insertTags: Array[String])(implicit s: Session) {
  var insertSeq: List[Tag] = List()
  for(tag <- insertTags) {
    insertSeq ++= new Tag(None, tag)
  }
  Tag.insertAll(insertSeq)

}

*Tag is the table Object

This is the preliminary code I have written. It doesn't work because insertAll() doesn't take Seq. I hope there is a way to do this...so it won't generate an array length times SQL insertion clause.

Didier Dupont · Accepted Answer · 2014-02-01 19:08:42Z

6

When a function expect repeated parameters such as U* and you want to pass a sequence of U instead, it must be marked as a sequence argument, which is done with : _* as in

Tag.insertAll(insertSeq: _*)

This is described in the specification in section 6.6. It disambiguates some situations such as ;

def f(x: Any*)
f(Seq(1, "a"))

There, f could be called with a single argument, Seq(1, "a") or two, 1 and "a". It will be the former, the latter is done with f(Seq(1, "a"): _*). Python has a similar syntax.

Regarding the questions in your comment : It works with Seq, collections that confoms to Seq, and values that can be implicitly converted to Seqs (which includes Arrays). This means a lot of collections, but not all of them. For instances, Set are not allowed (but they have a toSeq methods so it is still easy to call with a Set).

It is not a method, it it more like a type abscription. It simply tells the compiler that this the argument is the full expected Seq in itself, and not the only item in a sequence argument.

edited Feb 1, 2014 at 19:08

answered Feb 1, 2014 at 10:22

Didier Dupont

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2 Comments

windweller Over a year ago

Does this : _* sequence argument marker only apply to Seq or does it apply to some other collections as well? How does : _* this work if you don't mind me asking? Is it a method? A built in iteration of sort?

OlivierBlanvillain Over a year ago

See stackoverflow.com/questions/1124099/… and stackoverflow.com/questions/1124099/….

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