[ZODB-Dev] Ape newbie

[Shane Hathaway]

Adam Groszer wrote:
> Please help, I'm stuck
> 
> I brought together from the tests of Ape the attached script,
> tried to change the MappingGateway to write the data to MySQL.

This is a valiant attempt!

The fixed classifier and fixed persistent mapping are getting in your 
way.  The fixed classifier gives Ape the ability to load a state for 
TESTKEY and TEST2KEY even though you haven't stored anything for those 
keys yet.  The fixed persistent mapping forces the items of the root 
PersistentMapping to use particular OIDs.

Ape carefully avoids storing a new object over an existing object unless 
it can detect that the new object was derived from the existing object. 
  When testStoreAndLoad() tries to write to TestRoot and TestRoot2, it 
doesn't notice the root already has objects under those names.  The 
fixed persistent mapping assigns the OIDs of the new objects to the same 
OIDs that the old objects had, but at transaction commit Ape discovers 
that even though the old objects and the new objects have the same OIDs, 
the new objects were not derived from the old objects and you get a 
ConflictError.

I can see two options.  You can change testStoreAndLoad() so it modifies 
the existing TestRoot and TestRoot2 objects rather than replace them. 
This should be easy.  Or you can use a non-fixed classifier and 
non-fixed persistent mapping.  A non-fixed classifier would assign a new 
OID for each new object, allowing you to replace objects like you can in 
normal ZODB.  Unfortunately, there isn't yet a general-purpose 
classifier designed for use outside Zope.  (See apelib.zope2.classifier.)

One other thing that should help is adding the following line to end of 
setUp():

root_mapper.checkConfiguration()

This will detect configuration errors early.  It has sure helped me.

Shane