GridFS

GridFS is a specification for storing and retrieving files that exceed the BSON-document size limit of 16MB.

Instead of storing a file in a single document, GridFS divides a file into parts, or chunks, and stores each of those chunks as a separate document. By default GridFS limits chunk size to 256k. GridFS uses two collections to store files. One collection stores the file chunks, and the other stores file metadata.

When you query a GridFS store for a file, the driver or client will reassemble the chunks as needed. You can perform range queries on files stored through GridFS. You also can access information from arbitrary sections of files, which allows you to “skip” into the middle of a video or audio file.

GridFS is useful not only for storing files that exceed 16MB but also for storing any files for which you want access without having to load the entire file into memory. For more information on the indications of GridFS, see faq-developers-when-to-use-gridfs.

Using GridFS in Casbah

GridFS is a separate package in Casbah and to use it you must import it explicitly. See the full gridfs api docs for more information about the package.

Example use case:

import java.io.FileInputStream
import com.mongodb.casbah.Imports._
import com.mongodb.casbah.gridfs.Imports._

// Connect to the database
val mongoClient = MongoClient()("test")

// Pass the connection to the GridFS class
val gridfs = GridFS(mongoClient)

// Save a file to GridFS
val logo = new FileInputStream("mongo.png")
val id = gridfs(logo) { f =>
    f.filename = "mongodb_logo.png"
    f.contentType = "image/png"
}

// Find a file in GridFS by its ObjectId
val myFile = gridfs.findOne(id.get.asInstanceOf[ObjectId])

// Or find a file in GridFS by its filename
val myFile = gridfs.findOne("mongodb_logo.png")

// Print all filenames stored in GridFS
for (f <- gridfs) println(f.filename)

Joda DateTime

Due to hardcoding in the Java GridFS driver the Joda Time serialization hooks break with GridFS. It tries to explicitly cast certain date fields as a java.util.Date. To that end, on all find ops we explicitly unload the Joda Time deserializers and reload them when we’re done (if they were loaded before we started). This allows GridFS to always work but MAY cause thread safety issues - e.g. if you have another non-GridFS read happening at the same time in another thread at the same time, it may fail to deserialize BSON Dates as Joda DateTime - and blow up. Be careful — generally we don’t recommend mixing Joda Time and GridFS in the same JVM at the moment.