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:[email protected]', 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) ('00000', '[00000] [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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