Using Oracle Service Names with SQLAlchemy

问题:

I've run into a nasty little problem connecting to an Oracle schema via SQLAlchemy using a service name. Here is my code as a script. (items between angle brackets are place holders for real values for security reasons)

from sqlalchemy import create_engine  if __name__ == "__main__":                                                                                                                                                             engine = create_engine("oracle+cx_oracle://<username>:<password>@<host>/devdb")                                                                                                                                                        result = engine.execute("create table test_table (id NUMBER(6), name VARCHAR2(15) not NULL)")     result = engine.execute("drop table test_table") 

Where 'devdb' is a service name and not an SID. The result of running this script is the stack trace.

(oracle-test)[1]jgoodell@jgoodell-MBP:python$ python example.py  Traceback (most recent call last):   File "example.py", line 8, in <module>     result = engine.execute("create table test_table (id NUMBER(6), name VARCHAR2(15) not NULL)")   File "/Users/jgoodell/.virtualenvs/oracle-test/lib/python2.6/site-packages/sqlalchemy/engine/base.py", line 1621, in execute     connection = self.contextual_connect(close_with_result=True)   File "/Users/jgoodell/.virtualenvs/oracle-test/lib/python2.6/site-packages/sqlalchemy/engine/base.py", line 1669, in contextual_connect     self.pool.connect(),   File "/Users/jgoodell/.virtualenvs/oracle-test/lib/python2.6/site-packages/sqlalchemy/pool.py", line 272, in connect     return _ConnectionFairy(self).checkout()   File "/Users/jgoodell/.virtualenvs/oracle-test/lib/python2.6/site-packages/sqlalchemy/pool.py", line 425, in __init__     rec = self._connection_record = pool._do_get()   File "/Users/jgoodell/.virtualenvs/oracle-test/lib/python2.6/site-packages/sqlalchemy/pool.py", line 777, in _do_get     con = self._create_connection()   File "/Users/jgoodell/.virtualenvs/oracle-test/lib/python2.6/site-packages/sqlalchemy/pool.py", line 225, in _create_connection     return _ConnectionRecord(self)   File "/Users/jgoodell/.virtualenvs/oracle-test/lib/python2.6/site-packages/sqlalchemy/pool.py", line 318, in __init__     self.connection = self.__connect()   File "/Users/jgoodell/.virtualenvs/oracle-test/lib/python2.6/site-packages/sqlalchemy/pool.py", line 368, in __connect     connection = self.__pool._creator()   File "/Users/jgoodell/.virtualenvs/oracle-test/lib/python2.6/site-packages/sqlalchemy/engine/strategies.py", line 80, in connect     return dialect.connect(*cargs, **cparams)   File "/Users/jgoodell/.virtualenvs/oracle-test/lib/python2.6/site-packages/sqlalchemy/engine/default.py", line 279, in connect     return self.dbapi.connect(*cargs, **cparams) sqlalchemy.exc.DatabaseError: (DatabaseError) ORA-12505: TNS:listener does not currently know of SID given in connect descriptor  None None 

If 'devdb' were an SID and not a service name this example would work just fine, I've been trying different permutations of the connection string but haven't found anything that works. There also does not appear to be anything in the SQLAlchemy documentation that explicitly explains how to handle SID's verses service names for Oracle connections.

回答1:

I've found the answer you have to use the same connection string that would be used in a tnsnames.ora file in the connection string after the '@" like so

from sqlalchemy import create_engine  if __name__ == "__main__":                                                                                                                                                             engine = create_engine("oracle+cx_oracle://<username>:<password>@(DESCRIPTION = (LOAD_BALANCE=on) (FAILOVER=ON) (ADDRESS = (PROTOCOL = TCP)(HOST = <host>)(PORT = 1521)) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = devdb)))")                                                                                                                                                        result = engine.execute("create table test_table (id NUMBER(6), name VARCHAR2(15) not NULL)")     result = engine.execute("drop table test_table") 

This example runs just fine, and you can comment out the drop statement and check the DB to see that the table was created.

回答2:

import cx_Oracle dsnStr = cx_Oracle.makedsn('myhost','port','MYSERVICENAME') dsnStr = dsnStr.replace('SID', 'SERVICE_NAME') connect_str = 'oracle://user:password@' + dnsStr 

The makedns will create a TNS like this:

(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=myhost)(PORT=1530)))(CONNECT_DATA=(SID=MYSERVICENAME)))

replacing "SID" with "SERVICE_TYPE" got it to work for me.

---

If you are using flask, sqlalchemy, and oracle:

from flask import Flask from flask_sqlalchemy import SQLAlchemy import cx_Oracle  app = Flask(__name__) dnsStr = cx_Oracle.makedsn('my.host.com', '1530', 'my.service.name') dnsStr = dnsString.replace('SID', 'SERVICE_NAME') app.config['SQLALCHEMY_DATABASE_URI'] = 'oracle://myschema:mypassword@' + dnsStr db = SQLAlchemy(app) 

回答3:

cx_Oracle supports the passing of a service_name to the makedsn function.

http://cx-oracle.sourceforge.net/html/module.html?highlight=makedsn#cx_Oracle.makedsn

It would be nice if the create_engine() API passed the service_name through to the underlying call it makes to makedsn...something like this:

oracle = create_engine('oracle://user:pw@host:port', service_name='myservice')  TypeError: Invalid argument(s) 'service_name' sent to create_engine(), using configuration OracleDialect_cx_oracle/QueuePool/Engine. Please check that the keyword arguments are appropriate for this combination of components. 

文章来源: Using Oracle Service Names with SQLAlchemy