scala , Scala Retrieve aggregate pattern inside flat map


Scala Retrieve aggregate pattern inside flat map

Question:

Tag: scala

I have this scenario when trying to aggregate the result of few methods .

What im trying to do is im getting a Future of an object that contain a list of objects .

Then im flat mapping the future to a list of strings and then i would like to iterate this list

Than invoke couple of methods if it possible in a async way and then merge the result to one object i have to wait that all method will finish and send the result to a database.

This is where i stuck ....

UPDATE

I edit the method as suggested in the comments now i getting type mismatch error

expected List[postMd.PostMD]....

,

def getComplatePost(url: String): Unit = {
  val postMd = new PostMetaData
  val com = new Comments
  val post = new Post
  val fullPost = new CompletePost


  val postMdList: Future[List[postMd.PostMD]] = postMd.getPostMetaData(url, "396697410351933") // get the list of id
  postMdList.flatMap(x => {
    val fromid = x.map(_.fromID) //extract  the  Future to a list of string

   for {
    id <- fromid
    val c = com.getComments(id)
    val p = post.getPost(id)
  }yield (c,p)

  })
  }

thanks miki


Answer:

You can use a 'for - yield' this case. 'for' executes the yield operation after each of its statement completes.

This mainly hold as, 'for' is a syntactic sugar which further gets mapped to nested flatMap or map or foreach ... depending on the operations being performed.

Below is a modified snippet from your code:

for {
  id <- fromid
  //invoke methods
  c = com.getComments(id)
  p = post.getPost(id) 
  k = post.getPostLikes(id)
} // merge results and send data to DB

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