I am trying to create a column that stores sha1sums of content, and
allows easy programatic access of that content. I would like my table
definition to look like this
class Picture(Base):
content = sa.Column('content_sha1sum', DataColumn(se))
I would like to be able to create instances of pictures like this
p = Picture()
p.content(binary_image_string)
I only want to save the sha1sum to the database, DataColumn takes care
of computing the sha1sum, and actually saving the content to s3 or the
filesystem. I also want DataColumn to be a deferred column, I can do
that with deferred
All good so far.
What I can't do, or can't do cleanly is figure out how to access the
sha1sum behind content
p = s.query(Picture).all().first()
p.content_sha1sum
p.content_direct_url
Where direct_url is a function of the sha1sum. The problem with a
custom column is, I can't make sha1sum loading eager and the call to
s3/filesystem lazy, this means that every re-hydration of a Picture
requires a read from the filesystem.
There are a couple of ways that I could go. First would be to store
the sha1sum directly as a regular String column, and create properties
of names "content" and "content_direct_url". Another method would be
to use a mixin, but that is a bit ugly.
What I really want is a way to add all 3 properties with a single
line. I'm willing to modify DeclarativeMeta .
Any thoughts?
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