I have a developer who stores the binary copy of a file in his table. In
ColdFusion, this was acceptable, because he was writing every query by
hand, and could simply exclude that field. However, with the Django ORM it
is a bit of a problem. The primary table he uses is just for the file,
and has a file_name, file_type, file_size, and BinaryField.
The problem is that he has a database-level view that incorporates this
field, and it may be that he needs to keep this because other schemas in
our big-office Oracle use the view as an exported synonym.
What I advised him to do was to take the BinaryField out of the
database-level view, to protect the ORM from reading these large files into
memory, as in:
[obj for obj in LicensesDBView.objects.all()]
Or, if he cannot do that, to simply defer the field:
[obj for obj in
LicensesDBView.objects.defer('scanned_license').all()]
I was not sure whether to tell him to implement a ModelManager with a
get_queryset() method that defers the field, but it made me wonder whether
we should have a concept of an "initially deferred" field.
That is, this is a field that starts deferred, and can be pulled into the
select using a values iterator or a call to only() or defer(), e.g. the one
that cancels prior defers. The concept of "initially deferred" fields
would certainly require a new queryset method, such as "nodefer" which is
sort of like only but doesn't cause only those fields to load, or rather
defer could accept a syntax like defer('-scanned_license') to cancel that
previous deferred loading field.
I'm afraid I probably don't understand all the implications of this
feature, so I thought I'd bring it up on the list before filing any sort of
issue. Its likely this has been discussed before; I cannot do a historical
search all the time, especially when ancient history may not be today's
read on this issue.
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