On 7/24/15 10:13 AM, Richard Gerd Kuesters wrote:
hi!
first, /yes/, set and after_flush are quite different events :) but
here's what i'm trying to accomplish:
one object have an attribute, like 'state', and i would like to
monitor and trigger some other methods if (given scenarios):
1. the program sets a new value to a state that is equal to it's
actual state (and/or value), i can use 'set' but, does it reflect only
the value set or when it gets commited?
you set the value to the attribute, the "set" event receives it, if the
attribute already *had* that value loaded then the history is a no-net
change, no UPDATE is emitted. If the attribute did not already have a
value loaded, and the attribute does not specify "active_history", then
we don't know the "old" value and the history will show that the
attribute has changed, from a previous value of NO_VALUE.
I don't know what "does it reflect only the value set or when it gets
committed" means, hopefully the above answers your question.
1.1. and, if set to the same value, returning the old value (set with
retval=True) will make this object dirty (supposed to be the only
value modified) ?
the object goes into session.dirty as soon as any attributes are set.
however, in the flush, we go through the effort to look for actual net
changes. If there's no net change on the attribute, no UPDATE will be
emitted in the flush, the object moves back to clean at that point.
2. after_flush, if one of these entity get's modified, can i track
down what was modified, including my "state" column if possible?
yes you can look in session.dirty to find all the objects that are
dirty, then looking in "committed_state" will illustrate those attribute
that had something happen to them; though the latter part here is not a
"public" system - it will work for now but I can't guarantee that in a
future major version bump that system wouldn't change. We can add
public API to return ".modified", e.g. a list of keys that received a
modified event.
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