Lycovian <mfwil...@gmail.com> wrote:
> TL;DR:
> I'm trying to debug what is actually being sent to the pyodbc.connect
> function on connect in a custom dialect. I need to see the connection string
> that is being sent to the pyodbc.connect function *right* before it is sent
> but it has been difficult for me to unravel the layers of indirection on the
> create_engine call.
>
> Long version:
> If you care for more information I have this DSN related connect string for
> the custom dialect I am writing for Teradata:
> engine =
> sqlalchemy.create_engine("teradata://testsqlatd:password@td_testsqlatd",
> encoding='utf-8', echo=True)
>
> This connection string works and connects properly to my Teradata box (yay!).
>
> In my custom dialect I have subclassed so I can get some visibility into the
> ODBC connect string SQLA is constructing:
> def create_connect_args(self, url):
> connector = super(TeradataDialect_pyodbc,
> self).create_connect_args(url)
> print connector
> return connector
>
> This code appears to call sqlalchemy/connectors/pyodbc.py
> [create_connect_args]. And returns:
> [['dsn=td_testsqlatd;UID=testsqlatd;PWD=password'], {}]
>
> I assume that this string is roughly what is passed by SQLA to pyodbc at some
> future point as the ODBC connection string.
that is exactly the string that is passed to pyodbc. The examples at
http://docs.sqlalchemy.org/en/rel_0_9/dialects/mssql.html#additional-connection-examples
go into great detail with many examples of how this function works, even
without digging into the function itself.
> In my case the string above connects successfully. Oddly enough though UID
> is not a valid ODBC connection parameter for the Teradata ODBC driver. For
> Teradata the parameter must be Username. Same with PWD, this isn't valid for
> the Teradata ODBC driver. It should be Password.
>
> According to my testing and the Teradata ODBC docs the valid version of this
> ODBC connection string should be:
> 'dsn=td_testsqlatd;Username=testsqlatd;Password=password’
Well then it seems like your custom dialect might want to define its own
version of create_connect_args().
> I have verified directly with pyodbc that the first form of the connect
> string fails and the version directly above works, yet somehow in SQLAlchemy
> it connects. Because of this I believe that SQLA is rewriting the string
> further before connecting to the Teradata ODBC driver via pyodbc.
it is not. however, when we want to analyze things like this quickly, we can
use pdb.
Applying this patch:
diff --git a/lib/sqlalchemy/engine/default.py b/lib/sqlalchemy/engine/default.py
index a5af6ff..f0fb0ec 100644
--- a/lib/sqlalchemy/engine/default.py
+++ b/lib/sqlalchemy/engine/default.py
@@ -374,6 +374,8 @@ class DefaultDialect(interfaces.Dialect):
)
def connect(self, *cargs, **cparams):
+ import pdb
+ pdb.set_trace()
return self.dbapi.connect(*cargs, **cparams)
def create_connect_args(self, url):
then fire up a shell and run:
$ python
Python 2.7.5 (default, Mar 7 2014, 19:17:16)
[GCC 4.2.1 Compatible Apple LLVM 5.0 (clang-500.2.79)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from sqlalchemy import create_engine
>>> e = create_engine("mssql+pyodbc://scott:tiger@ms2005")
>>> e.connect()
> /Users/classic/dev/sqlalchemy/lib/sqlalchemy/engine/default.py(379)connect()
-> return self.dbapi.connect(*cargs, **cparams)
(Pdb) cargs
('dsn=ms2005;UID=scott;PWD=tiger',)
(Pdb) cparams
{}
(Pdb) self.dbapi
<module 'pyodbc' from
'/Users/classic/.python-eggs/pyodbc-3.0.7_beta10-py2.7-macosx-10.8-intel.egg-tmp/pyodbc.so'>
(Pdb)
we can verify this is the same thing that create_connect_args is giving us:
(Pdb) from sqlalchemy.engine import url
(Pdb)
self.create_connect_args(url.make_url("mssql+pyodbc://scott:tiger@ms2005"))
[['dsn=ms2005;UID=scott;PWD=tiger'], {}]
OK, a list and not a tuple, slight implementation detail. But there you have
it.
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