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The MongoGridFS class


Einführung

Utilities for storing and retrieving files from the database.

GridFS is a storage specification all supported drivers implement. Basically, it defines two collections: files, for file metadata, and chunks, for file content. If the file is large, it will automatically be split into smaller chunks and each chunk will be saved as a document in the chunks collection.

Each document in the files collection contains the filename, upload date, and md5 hash. It also contains a unique _id field, which can be used to query the chunks collection for the file's content. Each document in the chunks collection contains a chunk of binary data, a files_id field that matches its file's _id, and the position of this chunk in the overall file.

For example, the files document is something like:

array("_id" => 123456789, "filename" => "foo.txt", "chunkSize" => 3, "length" => 12)

and the chunks documents look like:

array("files_id" => 123456789, "n" => 0, "data" => new MongoBinData("abc"));
array("files_id" => 123456789, "n" => 1, "data" => new MongoBinData("def"));
array("files_id" => 123456789, "n" => 2, "data" => new MongoBinData("ghi"));
array("files_id" => 123456789, "n" => 3, "data" => new MongoBinData("jkl"));

Of course, the default chunk size is thousands of bytes, but that makes an unweildy example.

The MongoGridFS Family

MongoGridFS represents the files and chunks collections. MongoGridFS extends MongoCollection, and an instance of MongoGridFS has access to all of MongoCollection methods, which act on the files collection:

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$grid = $db->getGridFS(); $grid->update(array("filename" => "foo"), $newObj)); // update on the files collection

Another example of manipulating metadata:

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// save a file $id = $grid->storeFile("game.tgz"); $game = $grid->findOne(); // add a downloads counter $game->file['downloads'] = 0; $grid->save($game->file); // increment the counter $grid->update(array("_id" => $id), array('$inc' => array("downloads" => 1)));

You can also access the chunks collection from an instance of MongoGridFS:

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$chunks = $grid->chunks; // $chunks is a normal MongoCollection $chunks->insert(array("x" => 4));

There are some methods for MongoGridFS with the same name as MongoCollection methods, that behave slightly differently. For example, MongoGridFS::remove() will remove any objects that match the criteria from the files collection and their content from the chunks collection.

To store something new in GridFS, there are a couple options. If you have a filename, you can say:

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$grid->storeFile($filename, array("whatever" => "metadata", "you" => "want"));

If you have a string of bytes that isn't a file, you can also store that using MongoGridFS::storeBytes():

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$grid->storeBytes($bytes, array("whatever" => "metadata", "you" => "want");

Querying a MongoGridFS collection returns a MongoGridFSCursor, which behaves like a normal MongoCursor except that it returns MongoGridFSFiles instead of associative arrays.

MongoGridFSFiles can be written back to disc using MongoGridFSFile::write() or retrieved in memory using MongoGridFSFile::getBytes(). There is currently no method that automatically streams chunks, but it would be fairly easy to write by querying the $grid->chunks collection.

MongoGridFSFile objects contain a field file which contains any file metadata.

Klassenbeschreibung

MongoGridFS
extends MongoCollection {
/* Fields */
public MongoCollection $chunks = NULL ;
protected string $filesName = NULL ;
protected string $chunksName = NULL ;
/* Methods */
__construct ( MongoDB $db [, string $files = NULL [, string $chunks = NULL ]] )
public array drop ( void )
public MongoGridFSCursor find ([ array $query = array() [, array $fields = array() ]] )
public MongoGridFSFile findOne ([ mixed $query = array() ] )
public boolean remove ([ array $criteria = array() [, boolean $just_one = FALSE ]] )
public mixed storeBytes ( string $bytes [, array $extra = array() ] )
public mixed storeFile ( string $filename [, array $extra = array() ] )
public mixed storeUpload ( string $name [, string $filename ] )
}

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