For the past few years we've been using an ugly, but working, trick to
export data out of a Zope 3 instance without exporting every bit of
content. Given an object to export, we use
'locationCopy' (zope.location.pickling) to get a deep copy, set the
__parent__ attribute of the copied object to None, put it in the ZODB
root (root[EXPORT_KEY] = detached_copy), and then commit the
transaction. This is so that we have the 'oid' and connection needed
for ZODB's 'exportFile' to work.
If there's a better way of setting `__parent__` to None (or just not
following the __parent__ ref during Export, without affecting the
saved state in the database), I'd love to know. But that's an aside.
I exported some content tonight that had Blobs in it. Upon import, I
noticed that the blob files in the destination were empty (zero-
length). Looking at the ZEXP file, I could see the BLOBSTART markers,
but could see no binary data. Tracing down into the export, and then
just playing around with 'locationCopy' to make other detached copies,
I noticed that the Blob contents were never copied into the new file.
What can I do here? I'm in the midst of a botched deployment of some
content updates for a customer. I thought that copying something
'containing' a Blob would cause its contents to be copied. If this is
an exercise for application layer code, how can I get plugged in and
know when a Blob is being copied inside of a deep copy?
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