Mixing matching connectors and dialects in 0.6

[Bo Shi]

Hi All,

I'm attempting to get rudimentary support for a Vertica deployment
using an ODBC connector. According to their docs, their dialect is
mostly compatible with Oracle and SQLServer dialects. create_engine()
using 'mssql+pyodbc' seems to work but upon attempting to execute a
simple select statement, I get a programming error indicating the
following failed to run:

'SELECT user_name() as user_name;'

So it seems the dialect is getting some additional state under the
hood. lib/sqlalchemy/dialects/mssql/pyodbc.py appears to be hooking
PyODBCConnector and MSDialect together. Is it possible to specify
another dialect here? If so, is there any documentation on how to do
so?

[Michael Bayer]

Bo Shi wrote:
> Hi All,
>
> I'm attempting to get rudimentary support for a Vertica deployment
> using an ODBC connector. According to their docs, their dialect is
> mostly compatible with Oracle and SQLServer dialects.

That's funny because Oracle and SQL server are utterly, totally different
from a SQL quirks perspective. If I were to pick two dialects in SQLA
that were *most* different from each other and also non-standard, those
would be the two.

create_engine()
> using 'mssql+pyodbc' seems to work but upon attempting to execute a
> simple select statement, I get a programming error indicating the
> following failed to run:
>
> 'SELECT user_name() as user_name;'
>
>
> So it seems the dialect is getting some additional state under the
> hood. lib/sqlalchemy/dialects/mssql/pyodbc.py appears to be hooking
> PyODBCConnector and MSDialect together. Is it possible to specify
> another dialect here? If so, is there any documentation on how to do
> so?

you'd want to make yourself a "vertica" dialect module that imports the
PyODBCConnector and uses it as a mixin. I'd suggest copying one of the
existing dialects, and probably not the SQL server one unless you know
that vertica has a lot of the transact-SQL lineage that SQL server does
(the PG and SQLite dialects are the most barebones). To run it, add a
setup.py which configures your library as a setuptools entry point, in
this case the name would be "vertica+pyodbc":

from setuptools import setup

setup(name="SQLAVertica",
description="...",
entry_points={
'sqlalchemy:plugins':
['vertica+pyodbc = mypackage.base:VerticaDialect']
}

then using create_engine('vertica+pyodbc://user:pw@host/dbname') will load
in your dialect.

[Bo Shi]

> That's funny because Oracle and SQL server are utterly, totally different
> from a SQL quirks perspective.   If I were to pick two dialects in SQLA
> that were *most* different from each other and also non-standard, those
> would be the two.

I was a bit puzzled by this also (granted this was from some early
press release I dredged up* from google). I'm still working through
their documentation and haven't run across any configuration that
might enable a compatability mode yet.

* "improved compatibility with Oracle and SQLServer SQL dialects"
http://www.vertica.com/company/news_and_events/Vertica-Analytics-Database-2.5-The-Most-Cost-Effective-Way-To-Modernize-Data-Warehousing

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[Bo Shi]

Hi Michael,

Thanks for the tip on dialect creation; I have a working connection
and much of the low level library functionality appears to "just
work".

I've just started digging into the internals to begin implementing
introspection support. One issue I've encountered is that PyODBC
happens to return boolean columns as strings with values "1" and "0".
This confuses the current type system. I have skimmed the
TypeDecorator documentation but am still confused about how to
associate that with this custom dialect. Any hints?

I have attached the dialect base.py and a few test cases (not sure
they're useful as Vertica is frustratingly secretive about everything)
if you have time to review and comment.

[Femi Anthony]

Hi, I know this is a long time, but did you ever get SQLAlchemy to successfully work with Vertica ?

Please let me know as I am interested in doing the same.

Thanks,
Femi Anthony