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Document attachments
====================
.. contents:: Contents:
:local:
Reasoning
---------
The type of a Soledad document's content is `JSON <http://www.json.org/>`_,
which is good for efficient lookup and indexing. On the other hand, this is
particularly bad for storing larger amounts of binary data, because:
* the only way to store data in JSON is as unicode string, and this uses more
space than what is actually needed for binary data storage.
* upon synchronization, the content of a Soledad document needs to be
completelly transferred and decrypted for the document to be available for
use.
Document attachments were introduced as a means to efficiently store large
payloads of binary data while avoiding the need to wait for their transfer to
have access to the documents' contents.
Server-side
-----------
In the server, attachments are stored as :ref:`blobs`. See
:ref:`http-blobs-api` for more information on how to interact with the server
using HTTP.
The :ref:`IBlobsBackend <i-blobs-backend>` interface is provided, so in the
future there can be different ways to store attachments in the server side
(think of a third-party storage, for example). Currently, the
:ref:`filesystem-backend` is the only one that implements that interface.
Client-side
-----------
In the client, attachments are relations between JSON documents and blobs.
See :ref:`client-side-attachment-api` for reference.
Usage example
^^^^^^^^^^^^^
The attachments API is currently available in the `Document` class, and the
document needs to know about the store to be able to manage attachments. When
you create a new document with soledad, that document will already know about
the store that created it, and can put/get/delete an attachment:
.. code-block:: python
from twisted.internet.defer import inlineCallbacks
@inlineCallbacks
def attachment_example(soledad):
doc = yield soledad.create_doc({})
state = yield doc.get_attachment_state()
dirty = yield doc.is_dirty()
assert state == AttachmentStates.NONE
assert dirty == False
yield doc.put_attachment(open('hackers.txt'))
state = yield doc.get_attachment_state()
dirty = yield doc.is_dirty()
assert state | AttachmentState.LOCAL
assert dirty == True
yield soledad.put_doc(doc)
dirty = yield doc.is_dirty()
assert dirty == False
yield doc.upload_attachment()
state = yield doc.get_attachment_state()
assert state | AttachmentState.REMOTE
assert state == AttachmentState.SYNCED
fd = yield doc.get_attachment()
assert fd.read() == open('hackers.txt').read()
|
