[ZODB-Dev] Inconsistent use of ConflictError

[JohnD.Heintz]

Hear, hear!!

John


On Thursday 16 August 2001 13:31, Greg Ward wrote:
> This doesn't bother me much anymore now that we're not seeing
> ConflictError in practice (thanks to Connection.sync()), but it still
> bugs me that ZODB is inconsistent in how it uses ConflictError.
>
> In particular, ConflictError appears to be raised in no fewer than 6
> different ways throughout the ZODB/ZEO code (ignoring trivial
> differences like "raise ConflictError" vs. "raise
> POSException.ConflictError"):
>
>   raise ConflictError, `oid`
>
>   raise ConflictError(`oid`, `object.__class__`)
>
>   raise ConflictError, "transaction already invalidated"
>
>   raise POSException.ConflictError
>
>   raise POSException.ConflictError, (serial, oserial)
>
>   raise POSException.ConflictError(
>                         'serial number mismatch (was: %s, has: %s)' %
>                         (utils.U64(oserial), utils.U64(serial)))
>
> Do a recursive grep for "raise.*ConflictError" in StandaloneZODB to see
> for yourself.
>
> This inconsistency makes it pretty much impossible to do anything with
> the exception value; from an API point of view, all of the above might
> as well be a bare "raise ConflictError".
>
> Proposal:
>   * give ConflictError an actual interface, ie. some attributes,
>     a constructor with keyword arguments, and a __str__() to format
>     the error meaningfully
>   * fix all occurences of "raise ConflictError" to conform to
>     the new interface
>
> Here's a strawman class definition:
>
>   class ConflictError(TransactionError):
>       """
>
>       Instance attributes:
>         oid : string
>           the OID (8-byte packed string) of the object in conflict
>         klass_name : string
>           the fully-qualified name of that object's class
>         message : string
>           a human-readable explanation of the error
>         serials : (???, ???)
>           pair of mystery objects -- I have no idea what these are,
>           I'm just including them because bsddb3Storage/*.py want
>           to provide this info
>
>       """
>
>       def __init__(self, message=3DNone,
>                    oid=3DNone, klass_name=3DNone, serials=3DNone):
>           # message would default to something like
>           # "database conflict error"
>
>       def __str__ (self):
>           return self.message  # with some or all of oid, klass_name, a=
nd
>                                # serials pasted on in a meaningful way
>
> Hmmm, the ConflictError docstring should mention that conflicts can
> occur on read as well.
>
> Thoughts?
>
>         Greg

--=20
=2E . . . . . . . . . . . . . . . . . . . . . . .

John D. Heintz | Senior Engineer

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