Creating a file content type with preview

[Marcel Maré]

I'd like to create a file like content type with an image preview. For example when one uploads a pdf file a background process would create a series of images of pages. 

Since I'm not very familiar with Pyramid/Kotti yet I have some architectural questions: 

I don't know where to put the preview images. Could I (ab)use kotti.resources.Node.annotations for this? Or should I put the images in filedepot and store the references in the content type?

Where should I put code that should run when the user has posted the add-form? Override something from AddFormView?

Any pointers welcome. TIA

Marcel

[Andreas Kaiser]

I'd just add one or more Depot filters to my content type. Fortunately
Kotti makes that *very* easy:
https://kotti.readthedocs.org/en/testing/developing/advanced/blobs.html.
For a real world example see
https://github.com/Kotti/kotti_image/blob/master/kotti_image/resources.py.
You probably need to implement a custom filter, but should be about all
you need to do. Your uploaded files will be passed to the filter
whenever you add or edit a file and the filter will save whatever it
produces as an attachment to the actual file. After that it can be
accessed via the node's data attribute. Also see
http://depot.readthedocs.org/en/latest/database.html#custom-behaviour-in-attachments
on that topic.


HTH,

Andreas

[Marcel Maré]

Yes that makes sense. Didn't know that the depot functionality was exposed through the UploadedFileField.

Thanks again Andreas for the prompt reply.

Marcel

[Marcel Maré]

I noticed from the Image source code that kotti.resources.SaveDataMixin has an undocumented but handy data_filters property. That's nice to know.

[Marcel Maré]

I've hit a speed bump.

Since I want to use the data_filters class property (of the SaveDataMixin) I thought it best to create a content type identical to kotti.resources.File (because I think File cannot be subclassed). This is it, with only the name in the type_info changed. By marking it as an File implementer I hoped being able to reuse File's views. [Later I would create an additional view that would make use of the output of the datafilter]

@implementer(IFile)
class PreviewFile(SaveDataMixin, Content):
    id = Column(ForeignKey(Content.id), primary_key=True)

    type_info = Content.type_info.copy(
        name=u'PreviewFile',
        title=_(u'Preview File'),
        add_view=u'add_file',
        addable_to=[u'Document'],
        selectable_default_views=[],
        uploadable_mimetypes=['*', ],
    )

However the code doesn't work. See stack trace below. There seems to be a "data" member missing. I'd expect SaveDataMixin to provide this. 

What gives?

Marcel

Traceback (most recent call last):

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/bin/pserve", line 9, in <module>

    load_entry_point('pyramid', 'console_scripts', 'pserve')()

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/pyramid/scripts/pserve.py", line 58, in main

    return command.run()

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/pyramid/scripts/pserve.py", line 328, in run

    global_conf=vars)

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/pyramid/scripts/pserve.py", line 363, in loadapp

    return loadapp(app_spec, name=name, relative_to=relative_to, **kw)

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/paste/deploy/loadwsgi.py", line 247, in loadapp

    return loadobj(APP, uri, name=name, **kw)

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/paste/deploy/loadwsgi.py", line 272, in loadobj

    return context.create()

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/paste/deploy/loadwsgi.py", line 710, in create

    return self.object_type.invoke(self)

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/paste/deploy/loadwsgi.py", line 203, in invoke

    app = context.app_context.create()

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/paste/deploy/loadwsgi.py", line 710, in create

    return self.object_type.invoke(self)

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/paste/deploy/loadwsgi.py", line 146, in invoke

    return fix_call(context.object, context.global_conf, **context.local_conf)

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/paste/deploy/util.py", line 55, in fix_call

    val = callable(*args, **kw)

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/kotti/__init__.py", line 187, in main

    initialize_sql(engine)

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/kotti/resources.py", line 863, in initialize_sql

    populate()

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/kotti/populate.py", line 45, in populate

    if DBSession.query(Node.id).count() == 0:

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/sqlalchemy/orm/scoping.py", line 150, in do

    return getattr(self.registry(), name)(*args, **kwargs)

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/sqlalchemy/orm/session.py", line 1260, in query

    return self._query_cls(entities, self, **kwargs)

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/sqlalchemy/orm/query.py", line 110, in __init__

    self._set_entities(entities)

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/sqlalchemy/orm/query.py", line 120, in _set_entities

    self._set_entity_selectables(self._entities)

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/sqlalchemy/orm/query.py", line 137, in _set_entity_selectables

    ext_info.mapper._equivalent_columns

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/sqlalchemy/orm/query.py", line 153, in _mapper_loads_polymorphically_with

    for m2 in mapper._with_polymorphic_mappers or [mapper]:

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/sqlalchemy/util/langhelpers.py", line 747, in __get__

    obj.__dict__[self.__name__] = result = self.fget(obj)

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", line 1893, in _with_polymorphic_mappers

    configure_mappers()

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", line 2771, in configure_mappers

    Mapper.dispatch._for_class(Mapper).after_configured()

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/sqlalchemy/event/attr.py", line 218, in __call__

    fn(*args, **kw)

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/sqlalchemy/orm/events.py", line 613, in wrap

    fn(*arg, **kw)

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py", line 144, in after_configured

    self.cls.__declare_last__()

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/kotti/resources.py", line 664, in __declare_last__

    args = (mapper.attrs['data'], 'set', _SQLAMutationTracker._field_set)

  File "/Users/mjm/Dropbox/Devel/_Experiments/pyramid/venv2/lib/python2.7/site-packages/sqlalchemy/util/_collections.py", line 193, in __getitem__

    return self._data[key]

KeyError: 'data'

 

[Oshane Bailey]

Check out kotti_pdf, which creates a preview of the PDF file.