How to convert casbah mongodb list to json in scala / play

问题

I'm learning scala and mongodb at present and using the play! framework, so I'm making all sorts of mistakes as I get my head around things. Currently I have a scala object that returns a list of database objects returned from a mongodb query via casbah as follows;

object Alerts  {

   def list() : List[DBObject]= {

        val collection = MongoDatabase.collection;
        val query = MongoDBObject.empty
        val order = MongoDBObject("Issue Time:" -> -1)
        val list = collection.find(query).sort(order).toList
        list
   }

... }

Elsewhere in my code I wish to output the List of objects in Json - so I have;

  val currentAlerts = Alerts.list()

What I'd like to write is something like;

  val resultingJson = currentAlerts.toJson

But when I do this, I understandably get the following error;

  value toJson is not a member of List[com.mongodb.casbah.Imports.DBObject]

My question is - what's the right way to convert a List of com.mongodb.casbah.Imports.DBObject into Json for output?

EDIT:

For clarity, what I really want to do is the equivalent of

val listInJson = collection.find(query).sort(order).toJson

In the same way that I CAN write

val listAsString = collection.find(query).sort(order).toString

回答1:

You can try

com.mongodb.util.JSON.serialize(Alerts.list())

This should return a JSON array with your Alerts

回答2:

I have the following

def service() = Action {
 // connect
 val collection = MongoConnection()("someDB")("someCollection")
 // simply convert the result to a string, separating items with a comma
 // this string goes inside an "array", and it's ready to hit the road
 val json = "[%s]".format(
  collection.find(someQuery).toList.mkString(",")
 )

 Ok(json).as("application/json")

}

回答3:

I have what is a horrid solution as follows;

val currentAlerts = Alerts.list()

var jsonList : List[JsValue] = Nil

// Iterate over the DBObjects and use to String to convert each to JSON
// and then parse that back into the list so we can use toJson on it later.
// MAD, but works.

for (dbObject <- currentAlerts) {
    jsonList ::=  Json.parse(dbObject.toString)
}

val result = Json.toJson(jsonList)
Ok(result).as("application/json")

There must surely be a better way?

来源：https://stackoverflow.com/questions/11987071/how-to-convert-casbah-mongodb-list-to-json-in-scala-play

标签

scala

mongodb

playframework

casbah