Re: Migrating to BTrees 4.x

On Thu, Jan 5, 2017, at 19:01, Jim Fulton wrote:

> But surely people have built apps with BTrees 4, because BTrees 4 was
> released a loooooooong time ago (late 2012), and this seatbelt was
> introduced in BTrees 4.0.
> 

> When indexing content, you will very often encounter content without a
> value set, typically defaulting to None.
> 

> When such values are indexed, you'll get an error.  I don't see any
> guard against this error in, for example, zope.index.
> 

> Have people built newer apps with indexing on BTrees 4? If so, how
> have you dealt with this issue?


I've encountered this when working on Products.ZCatalog back in 2014. At
first I passed on the TypeError, and reraised it to get a more
application specific error message
(https://github.com/zopefoundation/Products.ZCatalog/commit/c378cdab2fb8997af1a17261458a1528e7131243)
.


Later on this was deemed to be too cumbersome, so in mid-2016 I've
changed this to simply ignore any call that tried to put None values
into a ZCatalog Unindex
(https://github.com/zopefoundation/Products.ZCatalog/commit/1b078be1e336998f87ecdfbfd04944ebc33d0af7)
.


Neither ZCatalog nor Zope2 have data migration frameworks, so
migrations of existing database is left to each application. I case of
Plone, there is a migration framework and while working on that, David
ran into this problem.


There's probably a Plone version being released that uses BTrees 4+ and
ZCatalog 3.1+ later this or next year.


I think this is all pretty much as expected, as the main feature
everyone wants from a new Zope2 version is Python 3 compatibility and
that is only very slowing making its way through the stack.


Hanno

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