I am using Mongo-Java-Driver 2.13 I stored a PDF file (size 30mb) in GridFS. I am able to perform insertion, deletion and find operation easily.
MongoClient mongo = new MongoClient("localhost", 27017);
DB db = mongo.getDB("testDB");
File pdfFile = new File("/home/dev/abc.pdf");
GridFS gfs = new GridFS(db,"books");
GridFSInputFile inputFile = gfs.createFile(pdfFile);
inputFile.setId("101");
inputFile.put("title", "abc");
inputFile.put("author", "xyz");
inputFile.save();
data is persisted in books.files and books.chunks collections. Now I want to update :
case 1: pdf file
case 2: title or author
How to perform these Update operations for Case 1 in GridFS ?
I came to know that I need to maintain multiple versions of my files and pick up the right version. Can anybody put some clarity on it?
Edit:
I can update metadata(title, author) easily.
GridFSDBFile outputFile = gfs.findOne(new BasicDBObject("_id", 101));
BasicDBObject updatedMetadata = new BasicDBObject();
updatedMetadata.put("name", "PG");
updatedMetadata.put("age", 22);
outputFile.setMetaData(newMetadata);
outputFile.save();
解决方案
In GridFS you are not removing/deleting a single document but actually a bunch of documents (files are split into chunks and each chunk is a separate document). That means replacing a file is simply not possible in an atomic manner.
What you can do instead is:
insert a new file with a new name
after this happened (use the replica acknowledged write-concern), update all references to the old file to point to the new one
after you got a confirmation for this, you can delete the old file
GridFS is kind of a hackish feature. It is often better to just use a separate fileserver with a real filesystem to store the file content and only store the metadata in MongoDB.