GridFS is a scalable MongoDB filesystem for storing and retrieving large files. The default limit for a MongoDB record is 16MB, so to store data that is larger than this limit, GridFS can be used. GridFS shards the data into smaller chunks automatically. See MongoDB documentation for details.
GridStore is a single file inside GridFS that can be managed by the script.
Opening a GridStore (a single file in GridFS) is a bit similar to opening a database. At first you need to create a GridStore object and then open it.
var gs = new mongodb.GridStore(db, filename, mode[, options])
Where
Example:
var gs = new mongodb.GridStore(db, "test.png", "w", {
"content_type": "image/png",
"metadata":{
"author": "Daniel"
},
"chunk_size": 1024*4
});
When GridStore object is created, it needs to be opened.
gs.open(callback);
callback gets two parameters - and error object (if error occured) and the GridStore object.
Opened GridStore object has a set of useful properties
Example
gs.open(function(err, gs){
console.log("this file was uploaded at "+gs.uploadDate);
});
Writing can be done with write
gs.write(data, callback)
where data is a Buffer or a string, callback gets two parameters - an error object (if error occured) and result value which indicates if the write was successful or not.
While the GridStore is not closed, every write is appended to the opened GridStore.
This function opens the GridStore, streams the contents of the file into GridStore, and closes the GridStore.
gs.writeFile( file, callback )
where
Reading from GridStore can be done with read
gs.read([size], callback)
where
You can stream data as it comes from the database using stream
gs.stream([autoclose=false])
where
The function returns read stream based on this GridStore file. It supports the events ‘read’, ‘error’, ‘close’ and ‘end’.
GridStore files can be unlinked with unlink
mongodb.GridStore.unlink(db, name, callback)
Where
GridStore needs to be closed after usage. This can be done with close
gs.close(callback)
Checking if a file exists in GridFS can be done with exist
mongodb.GridStore.exist(db, filename, callback)
Where
Seeking can be done with seek
gs.seek(position);
This function moves the internal pointer to the specified position.