SqlAlchemy equivalent of pyodbc connect string using FreeTDS

Question

The following works:

import pyodbc
pyodbc.connect('DRIVER={FreeTDS};Server=my.db.server;Database=mydb;UID=myuser;PWD=mypwd;TDS_Version=8.0;Port=1433;')

The following fails:

import sqlalchemy
sqlalchemy.create_engine("mssql://myuser:mypwd@my.db.server:1433/mydb?driver=FreeTDS& odbc_options='TDS_Version=8.0'").connect()

The error message for above is:

DBAPIError: (Error) ('08001', '[08001] [unixODBC][FreeTDS][SQL Server]Unable to connect to data source (0) (SQLDriverConnectW)') None None

Can someone please point me in the right direction? Is there a way I can simply tell sqlalchemy to pass a specific connect string through to pyodbc?

Please Note: I want to keep this DSN-less.

Answer 1

The example by @Singletoned would not work for me with SQLAlchemy 0.7.2. From the SQLAlchemy docs for connecting to SQL Server:

If you require a connection string that is outside the options presented above, use the odbc_connect keyword to pass in a urlencoded connection string. What gets passed in will be urldecoded and passed directly.

So to make it work I used:

import urllib
quoted = urllib.quote_plus('DRIVER={FreeTDS};Server=my.db.server;Database=mydb;UID=myuser;PWD=mypwd;TDS_Version=8.0;Port=1433;')
sqlalchemy.create_engine('mssql+pyodbc:///?odbc_connect={}'.format(quoted))

This should apply to Sybase as well.

NOTE: In python 3 the urllib module has been split into parts and renamed. Thus, this line in python 2.7:

quoted = urllib.quote_plus

has to be changed to this line in python3:

quoted = urllib.parse.quote_plus

Answer 2

I'm still interested in a way to do this in one line within the sqlalchemy create_engine statement, but I found the following workaround detailed here:

import pyodbc, sqlalchemy

def connect():
    pyodbc.connect('DRIVER={FreeTDS};Server=my.db.server;Database=mydb;UID=myuser;PWD=mypwd;TDS_Version=8.0;Port=1433;')

sqlalchemy.create_engine('mssql://', creator=connect)

UPDATE: Addresses a concern I raised in my own comment about not being able to pass arguments to the connect string. The following is a general solution if you need to dynamically connect to different databases at runtime. I only pass the database name as a parameter, but additional parameters could easily be used as needed:

import pyodbc
import os

class Creator:
    def __init__(self, db_name='MyDB'):
        """Initialization procedure to receive the database name"""
        self.db_name = db_name

    def __call__(self):
        """Defines a custom creator to be passed to sqlalchemy.create_engine
           http://stackoverflow.com/questions/111234/what-is-a-callable-in-python#111255"""
        if os.name == 'posix':
            return pyodbc.connect('DRIVER={FreeTDS};'
                                  'Server=my.db.server;'
                                  'Database=%s;'
                                  'UID=myuser;'
                                  'PWD=mypassword;'
                                  'TDS_Version=8.0;'
                                  'Port=1433;' % self.db_name)
        elif os.name == 'nt':
            # use development environment
            return pyodbc.connect('DRIVER={SQL Server};'
                                  'Server=127.0.0.1;'
                                  'Database=%s_Dev;'
                                  'UID=user;'
                                  'PWD=;'
                                  'Trusted_Connection=Yes;'
                                  'Port=1433;' % self.db_name)

def en(db_name):
    """Returns a sql_alchemy engine"""
    return sqlalchemy.create_engine('mssql://', creator=Creator(db_name))

Answer 3

Internally "my.db.server:1433" is passed as part of a connection string like SERVER=my.db.server:1433;.

Unfortunately unixODBC/FreeTDS won't accept a port in the SERVER bit. Instead it wants SERVER=my.db.server;PORT=1433;

To use the sqlalchemy syntax for a connection string, you must specify the port as a parameter.

sqlalchemy.create_engine("mssql://myuser:mypwd@my.db.server:1433/mydb?driver=FreeTDS& odbc_options='TDS_Version=8.0'").connect()

becomes:

sqlalchemy.create_engine("mssql://myuser:mypwd@my.db.server/mydb?driver=FreeTDS&port=1433& odbc_options='TDS_Version=8.0'").connect()

Answer 4

This works:

import sqlalchemy
sqlalchemy.create_engine("DRIVER={FreeTDS};Server=my.db.server;Database=mydb;UID=myuser;PWD=mypwd;TDS_Version=8.0;Port=1433;").connect()

In that format, SQLAlchemy just ignores the connection string and passes it straight on to pyodbc.

Update:

Sorry, I forgot that the uri has to be url-encoded, therefore, the following works:

import sqlalchemy
sqlalchemy.create_engine("DRIVER%3D%7BFreeTDS%7D%3BServer%3Dmy.db.server%3BDatabase%3Dmydb%3BUID%3Dmyuser%3BPWD%3Dmypwd%3BTDS_Version%3D8.0%3BPort%3D1433%3B").connect()

Answer 5

To pass various parameters to your connect function, it sounds like format string might do what you want:

def connect(server, dbname, user, pass):
  pyodbc.connect('DRIVER={FreeTDS};Server=%s;Database=%s;UID=%s;PWD=%s;TDS_Version=8.0;Port=1433;' % (server, dbname, user, pass))

And you would then call it with something like:

connect('myserver', 'mydatabase', 'myuser', 'mypass')

More info on format strings is here: http://docs.python.org/library/string.html#formatstrings