GridFS

Prerequisites

You must include the following import statements in your program to run the code examples in this guide:

import java.nio.ByteBuffer
import java.nio.charset.StandardCharsets
import org.mongodb.scala._
import org.mongodb.scala.bson.BsonObjectId
import org.mongodb.scala.gridfs._
import org.mongodb.scala.model.Filters
import tour.Helpers._
import scala.util.Success

Connect to a MongoDB Deployment

First, connect to a MongoDB deployment and declare and define a MongoDatabase instance.

The following code connects to a standalone MongoDB deployment running on localhost on port 27017:

val mongoClient: MongoClient = MongoClient()

To learn more about connecting to MongoDB deployments, see the Connect to MongoDB guide.

Create a GridFS Bucket

GridFS stores files in two collections:

• chunks: stores the file chunks

• files: stores file metadata

The two collections are in a common bucket and the collection names are prefixed with the bucket name.

The driver provides the GridFSBucket() method to create GridFSBucket instances:

val myDatabase = mongoClient.getDatabase("mydb")
// Create a gridFSBucket using the default bucket name "fs"
val gridFSBucket = GridFSBucket(myDatabase)

You can pass a bucket name to the GridFSBucket() method:

// Create a gridFSBucket with a custom bucket name "files"
val gridFSFilesBucket = GridFSBucket(myDatabase, "files")

Upload to GridFS

The GridFSBucket.uploadFromObservable() method reads the contents of an Observable[ByteBuffer] and saves it to the GridFSBucket instance.

You can use the GridFSUploadOptions type to configure the chunk size or include additional metadata.

The following example uploads the contents of a Observable[ByteBuffer] into GridFSBucket:

// Get the input stream
val observableToUploadFrom: Observable[ByteBuffer] = Observable(
  Seq(ByteBuffer.wrap("MongoDB Tutorial".getBytes(StandardCharsets.UTF_8)))
)
// Create some custom options
val options: GridFSUploadOptions = new GridFSUploadOptions()
    .chunkSizeBytes(358400)
    .metadata(Document("type" -> "presentation"))
val fileId: BsonObjectId = gridFSBucket
    .uploadFromObservable("mongodb-tutorial", observableToUploadFrom, options)
    .headResult()

Find Files Stored in GridFS

To find the files stored in the GridFSBucket, use the find() method.

The following example prints out the filename of each file stored:

gridFSBucket.find().results().foreach(file => println(s" - ${file.getFilename}"))

You can also provide a custom filter to limit the results returned. The following example prints out the filenames of all files in which the contentType value is an image/png value in the user-defined metadata document:

gridFSBucket
  .find(Filters.equal("metadata.contentType", "image/png"))
  .results()
  .foreach(file => println(s" > ${file.getFilename}"))

Download from GridFS

The downloadToObservable() method returns an Observable[ByteBuffer] that reads the contents from MongoDB.

To download a file by its file _id, pass the _id to the method. The following example downloads a file by its file _id:

val downloadById = gridFSBucket.downloadToObservable(fileId).results()

If you don't know the _id of the file but know the filename, then you can pass the filename to the downloadToObservable() method. By default, it will download the latest version of the file. Use the GridFSDownloadOptions class to configure which version to download.

The following example downloads the original version of the file named mongodb-tutorial:

val downloadOptions: GridFSDownloadOptions = new GridFSDownloadOptions().revision(0)
val downloadByName = gridFSBucket.downloadToObservable("mongodb-tutorial", downloadOptions).results()

Rename Files

If you need to rename a file, then use the rename() method.

The following example renames a file to mongodbTutorial:

val fileId: ObjectId = ... // ObjectId of a file uploaded to GridFS
gridFSBucket.rename(fileId, "mongodbTutorial").printResults()

Delete Files

To delete a file from the GridFSBucket, use the delete() method.

The following example deletes a file from the GridFSBucket:

val fileId: ObjectId = ... //ObjectId of a file uploaded to GridFS
gridFSBucket.delete(fileId).printResults()