cx_Oracle doesn't connect when using SID instead of service name on connection string

Question

I have a connection string that looks like this

con_str = "myuser/[email protected]:1521/ora1"

Where ora1 is the SID of my database. Using this information in SQL Developer works fine, meaning that I can connect and query without problems.

However, if I attempt to connect to Oracle using this string, it fails.

cx_Oracle.connect(con_str)

DatabaseError:  ORA-12514:  TNS:listener  does  not  currently  know  of  service  requested  in  connect  descriptor

This connection string format works if the ora1 is a service name, though.

I have seen other questions that seem to have the reverse of my problem (it works with SID, but not Service name)

• Using Oracle Service Names with SQLAlachemy
• Oracle SID and Service name; connection problems
• cx_Oracle & Connecting to Oracle DB Remotely

What is the proper way to connect to Oracle, using cx_Oracle, using an SID and not a service name? How do I do this without the need to adjust the TNSNAMES.ORA file? My application is distributed to many users internally and making changes to the TNSNAMES file is less than ideal when dealing with users without administrator privileges on their Windows machines. Additionally, when I use service name, I don't need to touch this file at all and would like it keep it that way.

Solution 1

I a similar scenario, I was able to connect to the database by using cx_Oracle.makedsn() to create a dsn string with a given SID (instead of the service name):

dsnStr = cx_Oracle.makedsn("oracle.sub.example.com", "1521", "ora1")

This returns something like

(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=oracle.sub.example.com)(PORT=1521)))(CONNECT_DATA=(SID=ora1)))

which can then be used with cx_Oracle.connect() to connect to the database:

con = cx_Oracle.connect(user="myuser", password="mypass", dsn=dsnStr)
print con.version
con.close()

Solution 2

For those looking for how to specify service_name instead of SID.

From changelog for SQLAlchemy 1.0.0b1 (released on March 13, 2015):

[oracle] [feature] Added support for cx_oracle connections to a specific service name, as opposed to a tns name, by passing ?service_name=<name> to the URL. Pull request courtesy Sławomir Ehlert.

The change introduces new, Oracle dialect specific option service_name which can be used to build connect string like this:

from sqlalchemy import create_engine
from sqlalchemy.engine import url

connect_url = url.URL(
    'oracle+cx_oracle',
    username='some_username',
    password='some_password',
    host='some_host',
    port='some_port',
    query=dict(service_name='some_oracle_service_name'))

engine = create_engine(connect_url)

Solution 3

If you are using sqlalchemy and ORACLE 12, the following seems to work.

from sqlalchemy import create_engine
con='oracle://user:password@hostname:1521/?service_name=DDDD'
engine = create_engine(con)

Note, you have to use the service name and not the SID. I don't know why, but the simple connection string that uses SID does not work.

Comments

[dmvianna]

The documentation is very clear. Just do cx_Oracle.makedsn("oracle.sub.example.com", "1521", service_name="ora1"), explicitly using the keyword service_name to differentiate it from the third argument (which is sid).

[S4nd33p]

Very useful, landed here after 2 days of search and it worked in less than 30 seconds. Terrific. Thanks a lot @Andreas Fester.

[Andreas Fester]

@S4nd33p Thanks, glad to hear that it helped :-)

[xappppp]

After one month of search, and playing with different kinds of directory and environment variable, this is the answer fianlly get me connectted to the server and start to pull data. Very nice

[Superdooperhero]

This is question about cx_Oracle not sqlalchemy