GridStore

GridStore is a single file inside GridFS that can be managed by the script.

Open a GridFS file

Opening a GridStore is similar to opening a database. First you create a GridStore object, then open it.

const gs = new GridStore(db, filename, mode[, options])

Where:

• db is the database object
• filename is the name of the file in GridFS that needs to be accessed/created
• mode indicates the operation, can be one of:
  • “r” (Read): Looks for the file information in fs.files collection, or creates a new id for this object.
  • “w” (Write): Erases all chunks if the file already exist.
• options can be used to specify metadata for the file, such as content_type, metadata and chunk_size

Example:

const gs = new GridStore(db, "test.png", "w", {
  "content_type": "image/png",
  "metadata":{
      "author": "Daniel"
  },
  "chunk_size": 1024*4
});

After a GridStore object is created, it can be opened.

gs.open(function(err, gs) {
  // gs is the intialized GridStore object
});

Opened GridStore objects have a set of useful exposed properties:

• gs.length - length of the file in bytes
• gs.contentType - the content type for the file
• gs.uploadDate - when the file was uploaded
• gs.metadata - metadata that was saved with the file
• gs.chunkSize - chunk size

Example

gs.open(function(err, gs){
  console.log("this file was uploaded at "+gs.uploadDate);
});

Writing to GridFS

Write to the GridStore object with the write function:

gs.write(data, callback)

data is a Buffer or a string. Callback gets two parameters - an error object (if an error occured) and a 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.

Writing a file to GridFS

The writeFile function opens the GridStore, streams the contents of the file into GridStore, and closes the GridStore.

gs.writeFile( file, callback )

where:

• file is a file descriptor, or a string file path
• callback is a function with two parameters - an error object (if an error occured) and the GridStore object.

Reading from a GridFS file

Use the read function to read from a GridStore object.

gs.read([size], callback)

Where:

• size is the length of the data to be read
• callback is a callback function with two parameters - an error object (if an error occured) and data (binary string)

Streaming from GridFS

You can stream data as it comes from the database using stream.

gs.stream()

The function returns a read stream based on this GridStore file. It supports the events ‘read’, ‘error’, ‘close’ and ‘end’.

Delete a GridFS file

Use the unlink function to delete GridStore files.

GridStore.unlink(db, name, callback)

Where:

• db is the database object
• name is either the name of a GridStore object or an array of GridStore object names
• callback is the callback function

Closing a GridFS file

GridStore needs to be closed after usage. Use the close function:

gs.close(callback)

Check if a GridFS file exists

Use the exist function to check if a file exists:

GridStore.exist(db, filename, callback)

Where:

• db is the database object
• filename is the name of the file to be checked or a regular expression
• callback is a callback function with two parameters - an error object (if an error occured) and a boolean value indicating if the file exists or not
  

Seek to a specific position for reading

Seeking within a file can be done with seek:

gs.seek(position);

This function moves the internal pointer to the specified position.