MongoDB Extended JSON

The Scala driver supports reading and writing BSON documents represented as MongoDB Extended JSON. Both variants are supported:

Furthermore, the Document provides two sets of convenience methods for this purpose:

  • Document.toJson(): a set of overloaded methods that convert a Document instance to a JSON string
  • Document(json): a set of overloaded static factory methods that convert a JSON string to a Document instance

Writing JSON

Consider the task of implementing a mongoexport-like tool using the Scala driver.

val fileName =    // initialize to the path of the file to write to
val collection =  // initialize the collection from which you want to query

val writer: PrintWriter = new PrintWriter(fileName)
collection.find().subscribe(
      (doc: Document) => output.write(s"${doc.toJson}\r\n"),
      (t: Throwable) => // handle failure,
      () => output.close())

The Document.toJson() method constructs an instance of a JsonWriter with its default settings, which will write in strict mode with no new lines or indentation.

You can override this default behavior by using one of the overloads of toJson(). As an example, consider the task of writing a JSON string that can be copied and pasted into the MongoDB shell:

import java.text.SimpleDateFormat

val fmt = new SimpleDateFormat("dd/MM/yy")
val first = fmt.parse("01/01/2014")
val second = fmt.parse("01/01/2015")
val doc = Document("startDate" -> Document("$gt" -> first, "$lt" -> second))
println(doc.toJson(new JsonWriterSettings(JsonMode.SHELL)))

This code snippet will print out MongoDB shell-compatible JSON, which can then be pasted into the shell:

{ "startDate" : { "$gt" : ISODate("2014-01-01T05:00:00.000Z"), "$lt" : ISODate("2015-01-01T05:00:00.000Z") } }

Reading JSON

Consider the task of implementing a mongoimport-like tool using the Java driver.

import scala.io.Source
val fileName =    // initialize to the path of the file to read from
val collection =  // initialize the collection from which you want to import to

try {
  for (json <- Source.fromFile(fileName).getLines()) {
    collection.insertOne(Document(json)).head()
  }
} catch {
  case ex: Exception => println("Bummer, an exception happened.")
}

The Document(json) companion helper method constructs an instance of a JsonReader with the given string and returns an instance of an equivalent Document instance. JsonReader automatically detects the JSON flavor in the string, so you do not need to specify it.

Note

In the tools examples directory, there is sample code for mongoimport and mongoexport. These examples are more fully featured than the above code snippets. They also provide an example of asynchronous error handling, as well as chaining observables to enforce insertion order on import.

Reading and Writing JSON Directly

If you do not need a document and only want to deal with JSON, you can use JsonObject to read and write JSON directly. JsonObject is simply a wrapper class that takes in a String in the constructor and returns the String in the getJson() method. Reading and writing JSON directly is more efficient than constructing a Document first and then calling toJson(), and it is also more efficient than calling Document#parse. The codec responsible for reading/writing JSON (JsonObjectCodec) is part of the default registry, so doing this is very simple and demonstrated by the following example:

val database: MongoDatabase = mongoClient.getDatabase("mydb")
val collection: MongoCollection[JsonObject] = database.getCollection("test")
collection.insertOne(new JsonObject("{hello: 1}")).printResults()
val jsonObject: SingleObservable[JsonObject] = collection.find.first()

Reading and Writing JSON with CustomSettings

You can also provide custom JsonWriterSettings to the JsonObjectCodec, by constructing the codec yourself and then creating your own registry:

val codecRegistry =
      fromRegistries(
        fromCodecs(new JsonObjectCodec(JsonWriterSettings
           .builder()
           .outputMode(JsonMode.EXTENDED)
           .build())),
        DEFAULT_CODEC_REGISTRY
      )
val database: MongoDatabase = mongoClient.getDatabase("mydb").withCodecRegistry(codecRegistry)
val collection: MongoCollection[JsonObject] = database.getCollection("test")
collection.insertOne(new JsonObject("{hello: 1}")).printResults()
val jsonObject: SingleObservable[JsonObject] = collection.find.first()
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