[ZODB-Dev] ExportImport.py: failing on import of extension class

[Jim Fulton]

On Apr 26, 2007, at 2:13 AM, Paul Winkler wrote:

> In ExportImport._importDuringCommit() I found this little gem:
>
>             pfile = StringIO(data)
>             unpickler = Unpickler(pfile)
>             unpickler.persistent_load = persistent_load
>
>             newp = StringIO()
>             pickler = Pickler(newp, 1)
>             pickler.persistent_id = persistent_id
>
>             pickler.dump(unpickler.load())
>             pickler.dump(unpickler.load())
>             data = newp.getvalue()
>
>
> What's with the two load-and-dump lines near the end?

It is transforming the pickles by assigning new object ids to the  
objects imported.
The unpickler unpickles the pickles into an internal format that can  
be creates without actually creating the original objects.  It  
collects object ids and reassigns them. The pickler then turns the  
internal data back into pickles with the new object ids.
This is done in 2 steps because database records consist of 2  
pickles.  The first has enough information to create a ghost. The  
second pickle contains the object state.


Jim

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