419f387bce
currently active, otherwise we can't see from the return value whether a given time predates the history set. The downside is that the caller may now need to check whether it got a history object or the same object back. - Legacy-Id: 4560
61 lines
2.2 KiB
Python
61 lines
2.2 KiB
Python
def find_history_active_at(obj, time):
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"""Assumes obj has a corresponding history model (e.g. obj could
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be Person with a corresponding PersonHistory model), then either
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returns the object itself if it was active at time, or the history
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object active at time, or None if time predates the object and its
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history (assuming history is complete).
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For this to work, the history model must use
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related_name="history_set" for the foreign key connecting to the
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live model, both models must have a "time" DateTimeField and a
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history object must be saved with a copy of the old values and
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old time when the time field changes.
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"""
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if obj.time <= time:
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return obj
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histories = obj.history_set.order_by('-time')
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for h in histories:
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if h.time <= time:
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return h
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return None
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def get_history_object_for(obj):
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"""Construct history object for obj, i.e. instantiate history
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object, copy relevant attributes and set a link to obj, but done
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save. Any customizations can be done by the caller afterwards.
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Many-to-many fields are not copied.
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The history model must use related_name="history_set" for the
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foreign key connecting to the live model for this function to be
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able to discover it."""
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history_model = obj.history_set.model
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h = history_model()
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# copy attributes shared between history and obj
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history_field_names = set(f.name for f in history_model._meta.fields)
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for field in obj._meta.fields:
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if field is not obj._meta.pk and field.name in history_field_names:
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setattr(h, field.name, getattr(obj, field.name))
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# try setting foreign key to obj
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key_name = obj._meta.object_name.lower()
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if key_name in history_field_names:
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setattr(h, key_name, obj)
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# we can't copy many-to-many fields as h isn't saved yet, leave
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# that to caller
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return h
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def copy_many_to_many_for_history(history_obj, obj):
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"""Copy basic many-to-many fields from obj to history_obj."""
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# copy many to many
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for field in obj._meta.many_to_many:
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if field.rel.through and field.rel.through._meta.auto_created:
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setattr(history_obj, field.name, getattr(obj, field.name).all())
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