On Feb 19, 2010, at 2:17 PM, James wrote:
Anyone heard of 4D? Probably not, but I would love to work with
SQLAlchemy and this database.
How hard is it to write a new dialect?
by all reports, including some new ones gained today at pycon, it is extremely
easy. provided your database is relational.
Anyone had luck using generic odbc (ie not mysql moduled to pyodbc) to
connect to various unsupported databases?
step 1, get pyodbc to connect to your database. that may be easy or may
involve contacting the pyodbc author for fixes.
step 2, create a .py file that imports the PyODBC connector as a mixin to
class YourDialect(), the same way as any other dialect, and make any changes
to the create_connect_args method as necessary in your subclass.
step 3, establish a setup.py for your application which establishes your
library as a setuptools entrypoint for sqlalchemy.dialects. the name you
give it is what you'd call upon in create_engine(). I'd suggest a name like
4d+pyodbc.
I've tried a couple connection strings, the biggest problem is 4D
doesn't have a database name.
# connect to the actual database
from sqlalchemy import create_engine
#using DSN
engine = create_engine('mysql+pyodbc://4D_v11_Dev/DEFAULT_SCHEMA')
#using URL
engine = create_engine('mysql://user:p...@127.0.0.1', module='pyodbc')
#another dialect with DSN = ERROR: AttributeError: 'str' object has
no attribute 'paramstyle'
engine = create_engine('mssql://4D_v11_Dev', module='pyodbc')
# yet another try
engine = create_engine('mysql+pyodbc://4D_v11_Dev')
# show me output
engine.echo = True
None of those work, I have some stack traces, but the gist is this:
# when used without a database name
sqlalchemy.exc.DBAPIError: (Error) ('08004', '[08004] Server rejected
the connection:\nFailed to parse statement.\r (1301)
(SQLExecDirectW)') 'SELECT DATABASE()' ()
# when I try to specify a name
sqlalchemy.exc.DBAPIError: (Error) ('0', '[0] [iODBC][Driver
Manager]dlopen({MySQL}, 6): image not found (0) (SQLDriverConnectW)')
None None
But connection directly via pyodbc does work
import pyodbc
cnxn = pyodbc.connect(DSN=4D_v11_Dev;UID=user;PWD=pass)
cursor = cnxn.cursor()
cursor.execute('select * from ODBCTest')
a=cursor.fetchall()
print 'pyodbc',a
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