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Dolmen zodb blob handlers

Project description

dolmen.blob is a layer above dolmen.file, using the ZODB blobs as a storage facility. It respects the IFile and the dolmen.file INamedFile interfaces.


In order to make sure that our BlobFile is functional, we test it against some common uses, implemented by zope.file.file.File, and dolmen.file.NamedFile:

>>> from dolmen.blob import BlobFile, IBlobFile

>>> blob = BlobFile()
>>> print blob.contentType
>>> blob.filename

>>> blob = BlobFile(data='mydata', filename="foo.txt")
>>> blob.filename
>>> blob.contentType
>>> blob.mimeType

>>> blob = BlobFile(data=u'some random data', filename="foo.txt")
>>> blob.filename
'some random data'

>>> blob = BlobFile(contentType="plain/text")
>>> blob.filename
>>> blob.contentType

>>> import cStringIO
>>> data = cStringIO.StringIO("mydata")
>>> blob = BlobFile(data=data)
>>> blob.getSize()
>>> blob.size

>>> from zope.size.interfaces import ISized
>>> sized = ISized(blob)
>>> sized
<zope.file.browser.Sized object at ...>
>>> sized.sizeForDisplay()
u'1 KB'
>>> sized.sizeForSorting()
('byte', 6)

>>> from zope.filerepresentation.interfaces import IReadFile, IWriteFile
>>> reader = IReadFile(blob)
>>> writer = IWriteFile(blob)

>>> reader.size()

>>> writer.write('changing data')
'changing data'
>>> reader.size()

Let’s verify the implementation in depth:

>>> from dolmen.file import INamedFile
>>> from zope.interface import verify
>>> import zope.file
>>> import

>>> blob = BlobFile(data='my data')
>>> verify.verifyObject(IBlobFile, blob)
>>> verify.verifyObject(INamedFile, blob)
>>> verify.verifyObject(, blob)
>>> verify.verifyObject(zope.file.interfaces.IFile, blob)


The ZODB blobs mimic a basic Python file and implement basic methods, like read, write, readlines, seek, etc. In order to provide a very pluggable and performant way to persist the datas, dolmen.file proposes a storage mechanism, based on adapters. This idea, originally implemented in z3c.blobfile, has been enhanced to rely on multi adapters, adapting an ZODB.interfaces.IBlob and a data object.

As seen above, in the compatibility section, the dolmen.blob.BlobFile handles String, Unicode and file-like objects, out of the box.


If the storage can’t find a way to persist the data, a dolmen.blob.StorageError exception is raised:

>>> blob = BlobFile(data={'something': 1})
Traceback (most recent call last):
StorageError: An error occured during the blob storage. Check the value type (<type 'dict'>). This value should implement IFile, IString or IUnicode (see `dolmen.builtins`).

Storage implementation

The example above shows us that the Dict object is not handled by dolmen.blob, out of the box. Let’s implement a storage for this usecase:

>>> import zope.component
>>> from ZODB.interfaces import IBlob
>>> from dolmen.builtins import IDict
>>> from dolmen.blob import IFileStorage

>>> def store_dict(blob, dictionnary):
...     dict_repr = repr(dictionnary.items())
...     fp ='w')
...     fp.write(dict_repr)
...     fp.close()
...     return True

>>> zope.component.provideAdapter(
...    store_dict, adapts=(IBlob, IDict), provides=IFileStorage)

>>> blob = BlobFile(data={'something': 1})
"[('something', 1)]"

Blob to blob storage

dolmen.blob provides a blob to blob copy, using shutils:

>>> source = BlobFile(data='Some data here')
>>> destination = BlobFile(data='')

>>> = source
'Some data here'

Mimetype and charset

dolmen.blob provides components implementing the zope.mimetype IContentTypeAware interface. It allows your content to be manipulated in order to set a mimetype and extensive headers coptions.

Several adapters are provided by zope.mimetype. We don’t want to review them all, but there are some interesting ones.

The IContentInfo components allow you to get detailed information for your content, formatted in a convenient way, to publish them easily:

>>> from zope.interface import alsoProvides
>>> from zope.mimetype.interfaces import IContentInfo

>>> blob = BlobFile(data=u'some random data', filename="foo.txt")
>>> info = IContentInfo(blob)
>>> print info
<zope.mimetype.contentinfo.ContentInfo object at ...>
>>> print info.effectiveMimeType
>>> print info.effectiveParameters

It allows a rough handling of the data encoding too:

>>> from zope.mimetype.interfaces import IContentTypeEncoded

>>> encoded = BlobFile(data=u'La Pe\xf1a',
...                    parameters={'charset': 'utf-8'})

>>> info = IContentInfo(encoded)
>>> print info.effectiveParameters

>>> alsoProvides(encoded, IContentTypeEncoded)
>>> info = IContentInfo(encoded)

>>> info.effectiveParameters
{'charset': 'utf-8'}

>>> info.effectiveMimeType

>>> info.contentType

>>> codec = info.getCodec()


Filesystem access

In some cases, it’s useful to be able to be able to get the location of the physical blob file on the filesystem. This is possible through the attribute physical_path. However, this attribute is available only when the file has been persisted and the transaction commited:

>>> import transaction
>>> root = getRootFolder()
>>> root['myblob'] = BlobFile(data='my data', filename="data.txt")

The transaction has not been commited, we try to access the attribute:

>>> myblob = root['myblob']
>>> print myblob.physical_path

We now commit the transaction and retry:

>>> transaction.commit()
>>> print myblob.physical_path

Browser access

As an dolmen.file.INamedFile, the BlobFile can bee accessed by the browser, using a “file_publish” view:

>>> from zope.component import getMultiAdapter
>>> from zope.publisher.browser import TestRequest

>>> request = TestRequest()
>>> view = getMultiAdapter((myblob, request), name='file_publish')
>>> view
<dolmen.blob.access.FilePublisher object at ...>

>>> view.update()
>>> for key, value in view.response.getHeaders(): print key, repr(value)
X-Powered-By 'Zope (, Python ('
Content-Length '7'
Content-Type 'text/plain'
Content-Disposition 'attachment; filename="data.txt"'

>>> view.render()
< object at ...>


The persistency of the data can be handled, in complex object, by a FileField using a BlobProperty:

>>> from persistent import Persistent
>>> from dolmen.file import FileField
>>> from dolmen.blob import BlobProperty
>>> from zope.interface import Interface, implements

>>> class IContent(Interface):
...     binary = FileField(title=u"Binary data")

>>> class MyContent(Persistent):
...     implements(IContent)
...     binary = BlobProperty(IContent['binary'])

>>> root['mammoth'] = MyContent()
>>> manfred = root['mammoth']
>>> manfred.binary = 'Foobar'
>>> manfred.binary
<dolmen.blob.file.BlobValue object at ...>

>>> verify.verifyObject(IBlobFile, manfred.binary)
>>> ISized(manfred.binary).sizeForDisplay()
u'1 KB'

Copy using zope.copy

A copy hook exists for IBlob objects. It allows to copy stored blobs transparently, while working with zope.copy:

>>> import zope.copy

>>> source = BlobFile(data='Some data here')
>>> target = zope.copy.copy(source)
'Some data here'

It works recursiverly:

>>> from zope.container.btree import BTreeContainer
>>> root['gunther'] = BTreeContainer()
>>> root['gunther']['mammoth'] = MyContent()

>>> manfred = root['gunther']['mammoth']
>>> manfred.binary = 'Some data with no interest'
>>> manfred.binary.filename = u"filename.txt"
>>> manfred.binary.mimeType = "text/plain"

>>> copy_of_gunther = zope.copy.copy(root['gunther'])
>>> judith = copy_of_gunther['mammoth']

'Some data with no interest'
>>> judith.binary.filename
>>> judith.binary.mimeType


0.4 (2009-11-18)

  • Added ICopyHook for ZODB.interfaces.IBlob objects. Now the data is copied using zope.copy.

0.3 (2009-11-08)

  • Added Blob to Blob copy, using a new storage. Added tests for this new storage.

0.2.1 (2009-10-23)

  • Corrected a bug of a variable used when not defined, if a mimeType was given using the contentType argument at the BlobValue creation. Added a test to fix this behavior.

0.2 (2009-10-23)

  • Added a bunch of new tests for the compatibility with the new packages used.

  • A new access view is available for IBlobFile objects, returning a This access view also uses an adapter to zope.mimetype.interfaces.IContentInfo to get the header values.

  • IBlobFile now inherits from zope.file.interfaces.IFile. This brings in a lot of new features, including the compatibility with the zope.mimetype package and its adapters.

  • dolmen.blob now proposes a non Persistent blob, called BlobValue. It allows to have object storing an attribute value in a blob, without getting an independant connection to the database (Blob already do that). The BlobProperty uses this new component now.

0.1 (2009-10-19)

  • Initial release

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