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On 11/12/2012 07:55 AM, Ionuț Arțăriși wrote:
> Hi,
> 
> I submitted a patch for review last week[1] which started a discussion
> about implementing sqlalchemy dialect specific datatypes
> (e.g. postgresql, mysql etc.).
> 
> I think it would be great to abstract some common datatypes (such as for
> ip addresses) so we can then add custom validations or use different
> backend datatypes where that makes sense.

I also think this is a good idea. It's painful to see CHAR(32) used for
things like UUIDs stored as hex string values and VARCHAR(255) used to
store IPv4 addresses, which are simply unsigned 4-byte integers.

> The way the IPAddress is implemented should be pretty straightforward and
> very backwards compatible (the INET datatype acts as a string for basic
> operations). Just defining a new datatype:
> 
> IPAddress = lambda: String(255).with_variant(postgresql.INET(),
> 'postgresql')

Might be good to name it IPv4Address instead of IPAddress, even though
PostgreSQL's INET type supports both.

With MySQL, you can use the INET_ATON() and INET_NTOA() functions (in
SQLAlchemy' func.inet_aton as well...) to do the conversion to and from
the underlying unsigned integer and extend an existing SQLAlchemy data
type as shown here:

http://docs.sqlalchemy.org/en/rel_0_7/core/types.html#augmenting-existing-types

> which can then be used instead of the string like so:
> 
> access_ip_v4 = Column(IPAddress())
>
> I guess now there's the question of where we want to store these
> custom dataypes' implementations. Would it be enough to have a datatypes.py
> module in there and have all our custom types inside?

That would be fine with me -- especially if it was in Oslo eventually :)

Best,
-jay

> [1] https://review.openstack.org/#/c/15566/
> 
> -Ionuț
> 
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