On Tuesday, December 4, 2012 4:15:03 PM UTC-5, Jason wrote:
>
> Ok I figured out the cause, but not the solution. I am using a mutable
> type for hstore columns. I have a UserDefinedType for Hstore that just
> passes everything through to psycopg2's hstore type:
>
> class HStore(UserDefinedType):
> """ SQLAlchemy type that passes through values to be handled by a
> psycopg2
> extension type.
> """
> type_name = 'HSTORE'
>
> def get_col_spec(self):
> return self.type_name
>
> def bind_processor(self, dialect):
> return None
>
> def result_processor(self, dialect, coltype):
> return None
>
> def is_mutable(self):
> return True
>
> def copy_value(self, value):
> return copy.copy(value)
>
>
> I used the MutationDict from
> http://docs.sqlalchemy.org/en/rel_0_7/orm/extensions/mutable.html :
>
> class MutationDict(Mutable, dict):
>
> @classmethod
> def coerce(cls, key, value):
> "Convert plain dictionaries to MutationDict."
>
> if not isinstance(value, MutationDict):
> if isinstance(value, dict):
> return MutationDict(value)
>
> # this call will raise ValueError
> return Mutable.coerce(key, value)
> else:
> return value
>
> def __setitem__(self, key, value):
> "Detect dictionary set events and emit change events."
>
> dict.__setitem__(self, key, value)
> self.changed()
>
> def __delitem__(self, key):
> "Detect dictionary del events and emit change events."
>
> dict.__delitem__(self, key)
> self.changed()
>
>
> The column definition I use is:
>
> some_attrs = Column(MutationDict.as_mutable(HStore))
>
> Then in the actual transaction I am copying one object with that column
> definition to another object with the same definition:
>
> newobject.some_attrs = other_object.some_attrs
>
>
> If I comment out that line there is only a single flush at the commit
> time.
>
> It looks correct according to the examples I have seen, but if you know
> why it keeps setting them as dirty please let me know.
>
> On Tuesday, December 4, 2012 3:16:24 PM UTC-5, Michael Bayer wrote:
>>
>>
>> On Dec 4, 2012, at 3:04 PM, Jason wrote:
>>
>> After upgrading to SQLAlchemy 0.7.9 I know receive an error "FlushError:
>> Over 100 subsequent flushes have occurred within session.commit() - is an
>> after_flush() hook creating new objects?" which is was introduced by
>> http://docs.sqlalchemy.org/en/latest/changelog/changelog_07.html#change-75a53327aac5791fe98ec087706a2821in
>> the changelog.
>>
>> I don't have any after_flush event handlers. I do have a before_flush
>> event handler that changes the state of a related object, but that doesn't
>> sound like what the error is talking about.
>>
>> How can I debug this further? I am doing this within a Pyramid
>> application, so I am somewhat removed from the commit logic.
>>
>>
>> this error traps the condition that dirty state remains in the Session
>> after a flush has completed. This is possible if an after_flush hook has
>> added new state, or perhaps also if a mapper.after_update/after_insert etc
>> hook, or even a before_update/before_insert has modified the flush plan,
>> which is not appropriate in any case.
>>
>> the best way is to actually create an after_flush() hook with a
>> "pdb.set_trace()" in it; in there, you'd just look at session.new,
>> session.dirty, and session.deleted to ensure that they are empty.
>>
>>
Looks like copy.copy will call __setitem__ on dict to be copied resulting
in it being marked dirty. I had to change the copy code to:
def copy_value(self, value):
try:
# Use dict.copy(), because copy.copy will call __setitem__ on
the
# value causing it to be marked dirty, which could result in
# an infinite loop of flushing dirty copies if an hstore is
# copied to another hstore column.
return value.copy()
except Exception:
return None
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