sqlalchemy.dialects.oracle.cx_oracle

.. dialect:: oracle+cx_oracle :name: cx-Oracle :dbapi: cx_oracle :connectstring: oracle+cx_oracle://user:pass@hostname:port[/dbname][?service_name=<service>[&key=value&key=value...]] :url: https://oracle.github.io/python-cx_Oracle/ DSN vs. Hostname connections ----------------------------- cx_Oracle provides several methods of indicating the target database. The dialect translates from a series of different URL forms. Hostname Connections with Easy Connect Syntax ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Given a hostname, port and service name of the target Oracle Database, for example from Oracle's `Easy Connect syntax <https://cx-oracle.readthedocs.io/en/latest/user_guide/connection_handling.html#easy-connect-syntax-for-connection-strings>`_, then connect in SQLAlchemy using the ``service_name`` query string parameter:: engine = create_engine("oracle+cx_oracle://scott:tiger@hostname:port/?service_name=myservice&encoding=UTF-8&nencoding=UTF-8") The `full Easy Connect syntax <https://www.oracle.com/pls/topic/lookup?ctx=dblatest&id=GUID-B0437826-43C1-49EC-A94D-B650B6A4A6EE>`_ is not supported. Instead, use a ``tnsnames.ora`` file and connect using a DSN. Connections with tnsnames.ora or Oracle Cloud ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Alternatively, if no port, database name, or ``service_name`` is provided, the dialect will use an Oracle DSN "connection string". This takes the "hostname" portion of the URL as the data source name. For example, if the ``tnsnames.ora`` file contains a `Net Service Name <https://cx-oracle.readthedocs.io/en/latest/user_guide/connection_handling.html#net-service-names-for-connection-strings>`_ of ``myalias`` as below:: myalias = (DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = mymachine.example.com)(PORT = 1521)) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = orclpdb1) ) ) The cx_Oracle dialect connects to this database service when ``myalias`` is the hostname portion of the URL, without specifying a port, database name or ``service_name``:: engine = create_engine("oracle+cx_oracle://scott:tiger@myalias/?encoding=UTF-8&nencoding=UTF-8") Users of Oracle Cloud should use this syntax and also configure the cloud wallet as shown in cx_Oracle documentation `Connecting to Autononmous Databases <https://cx-oracle.readthedocs.io/en/latest/user_guide/connection_handling.html#connecting-to-autononmous-databases>`_. SID Connections ^^^^^^^^^^^^^^^ To use Oracle's obsolete SID connection syntax, the SID can be passed in a "database name" portion of the URL as below:: engine = create_engine("oracle+cx_oracle://scott:tiger@hostname:1521/dbname?encoding=UTF-8&nencoding=UTF-8") Above, the DSN passed to cx_Oracle is created by ``cx_Oracle.makedsn()`` as follows:: >>> import cx_Oracle >>> cx_Oracle.makedsn("hostname", 1521, sid="dbname") '(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=hostname)(PORT=1521))(CONNECT_DATA=(SID=dbname)))' Passing cx_Oracle connect arguments ----------------------------------- Additional connection arguments can usually be passed via the URL query string; particular symbols like ``cx_Oracle.SYSDBA`` are intercepted and converted to the correct symbol:: e = create_engine( "oracle+cx_oracle://user:pass@dsn?encoding=UTF-8&nencoding=UTF-8&mode=SYSDBA&events=true") .. versionchanged:: 1.3 the cx_oracle dialect now accepts all argument names within the URL string itself, to be passed to the cx_Oracle DBAPI. As was the case earlier but not correctly documented, the :paramref:`_sa.create_engine.connect_args` parameter also accepts all cx_Oracle DBAPI connect arguments. To pass arguments directly to ``.connect()`` without using the query string, use the :paramref:`_sa.create_engine.connect_args` dictionary. Any cx_Oracle parameter value and/or constant may be passed, such as:: import cx_Oracle e = create_engine( "oracle+cx_oracle://user:pass@dsn", connect_args={ "encoding": "UTF-8", "nencoding": "UTF-8", "mode": cx_Oracle.SYSDBA, "events": True } ) Note that the default value for ``encoding`` and ``nencoding`` was changed to "UTF-8" in cx_Oracle 8.0 so these parameters can be omitted when using that version, or later. Options consumed by the SQLAlchemy cx_Oracle dialect outside of the driver -------------------------------------------------------------------------- There are also options that are consumed by the SQLAlchemy cx_oracle dialect itself. These options are always passed directly to :func:`_sa.create_engine` , such as:: e = create_engine( "oracle+cx_oracle://user:pass@dsn", coerce_to_decimal=False) The parameters accepted by the cx_oracle dialect are as follows: * ``arraysize`` - set the cx_oracle.arraysize value on cursors, defaulted to 50. This setting is significant with cx_Oracle as the contents of LOB objects are only readable within a "live" row (e.g. within a batch of 50 rows). * ``auto_convert_lobs`` - defaults to True; See :ref:`cx_oracle_lob`. * ``coerce_to_decimal`` - see :ref:`cx_oracle_numeric` for detail. * ``encoding_errors`` - see :ref:`cx_oracle_unicode_encoding_errors` for detail. .. _cx_oracle_sessionpool: Using cx_Oracle SessionPool --------------------------- The cx_Oracle library provides its own connection pool implementation that may be used in place of SQLAlchemy's pooling functionality. This can be achieved by using the :paramref:`_sa.create_engine.creator` parameter to provide a function that returns a new connection, along with setting :paramref:`_sa.create_engine.pool_class` to ``NullPool`` to disable SQLAlchemy's pooling:: import cx_Oracle from sqlalchemy import create_engine from sqlalchemy.pool import NullPool pool = cx_Oracle.SessionPool( user="scott", password="tiger", dsn="orclpdb", min=2, max=5, increment=1, threaded=True, encoding="UTF-8", nencoding="UTF-8" ) engine = create_engine("oracle+cx_oracle://", creator=pool.acquire, poolclass=NullPool) The above engine may then be used normally where cx_Oracle's pool handles connection pooling:: with engine.connect() as conn: print(conn.scalar("select 1 FROM dual")) As well as providing a scalable solution for multi-user applications, the cx_Oracle session pool supports some Oracle features such as DRCP and `Application Continuity <https://cx-oracle.readthedocs.io/en/latest/user_guide/ha.html#application-continuity-ac>`_. Using Oracle Database Resident Connection Pooling (DRCP) -------------------------------------------------------- When using Oracle's `DRCP <https://www.oracle.com/pls/topic/lookup?ctx=dblatest&id=GUID-015CA8C1-2386-4626-855D-CC546DDC1086>`_, the best practice is to pass a connection class and "purity" when acquiring a connection from the SessionPool. Refer to the `cx_Oracle DRCP documentation <https://cx-oracle.readthedocs.io/en/latest/user_guide/connection_handling.html#database-resident-connection-pooling-drcp>`_. This can be achieved by wrapping ``pool.acquire()``:: import cx_Oracle from sqlalchemy import create_engine from sqlalchemy.pool import NullPool pool = cx_Oracle.SessionPool( user="scott", password="tiger", dsn="orclpdb", min=2, max=5, increment=1, threaded=True, encoding="UTF-8", nencoding="UTF-8" ) def creator(): return pool.acquire(cclass="MYCLASS", purity=cx_Oracle.ATTR_PURITY_SELF) engine = create_engine("oracle+cx_oracle://", creator=creator, poolclass=NullPool) The above engine may then be used normally where cx_Oracle handles session pooling and Oracle Database additionally uses DRCP:: with engine.connect() as conn: print(conn.scalar("select 1 FROM dual")) .. _cx_oracle_unicode: Unicode ------- As is the case for all DBAPIs under Python 3, all strings are inherently Unicode strings. In all cases however, the driver requires an explicit encoding configuration. Ensuring the Correct Client Encoding ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ The long accepted standard for establishing client encoding for nearly all Oracle related software is via the `NLS_LANG <https://www.oracle.com/database/technologies/faq-nls-lang.html>`_ environment variable. cx_Oracle like most other Oracle drivers will use this environment variable as the source of its encoding configuration. The format of this variable is idiosyncratic; a typical value would be ``AMERICAN_AMERICA.AL32UTF8``. The cx_Oracle driver also supports a programmatic alternative which is to pass the ``encoding`` and ``nencoding`` parameters directly to its ``.connect()`` function. These can be present in the URL as follows:: engine = create_engine("oracle+cx_oracle://scott:tiger@orclpdb/?encoding=UTF-8&nencoding=UTF-8") For the meaning of the ``encoding`` and ``nencoding`` parameters, please consult `Characters Sets and National Language Support (NLS) <https://cx-oracle.readthedocs.io/en/latest/user_guide/globalization.html#globalization>`_. .. seealso:: `Characters Sets and National Language Support (NLS) <https://cx-oracle.readthedocs.io/en/latest/user_guide/globalization.html#globalization>`_ - in the cx_Oracle documentation. Unicode-specific Column datatypes ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ The Core expression language handles unicode data by use of the :class:`.Unicode` and :class:`.UnicodeText` datatypes. These types correspond to the VARCHAR2 and CLOB Oracle datatypes by default. When using these datatypes with Unicode data, it is expected that the Oracle database is configured with a Unicode-aware character set, as well as that the ``NLS_LANG`` environment variable is set appropriately, so that the VARCHAR2 and CLOB datatypes can accommodate the data. In the case that the Oracle database is not configured with a Unicode character set, the two options are to use the :class:`_types.NCHAR` and :class:`_oracle.NCLOB` datatypes explicitly, or to pass the flag ``use_nchar_for_unicode=True`` to :func:`_sa.create_engine`, which will cause the SQLAlchemy dialect to use NCHAR/NCLOB for the :class:`.Unicode` / :class:`.UnicodeText` datatypes instead of VARCHAR/CLOB. .. versionchanged:: 1.3 The :class:`.Unicode` and :class:`.UnicodeText` datatypes now correspond to the ``VARCHAR2`` and ``CLOB`` Oracle datatypes unless the ``use_nchar_for_unicode=True`` is passed to the dialect when :func:`_sa.create_engine` is called. .. _cx_oracle_unicode_encoding_errors: Encoding Errors ^^^^^^^^^^^^^^^ For the unusual case that data in the Oracle database is present with a broken encoding, the dialect accepts a parameter ``encoding_errors`` which will be passed to Unicode decoding functions in order to affect how decoding errors are handled. The value is ultimately consumed by the Python `decode <https://docs.python.org/3/library/stdtypes.html#bytes.decode>`_ function, and is passed both via cx_Oracle's ``encodingErrors`` parameter consumed by ``Cursor.var()``, as well as SQLAlchemy's own decoding function, as the cx_Oracle dialect makes use of both under different circumstances. .. versionadded:: 1.3.11 .. _cx_oracle_setinputsizes: Fine grained control over cx_Oracle data binding performance with setinputsizes ------------------------------------------------------------------------------- The cx_Oracle DBAPI has a deep and fundamental reliance upon the usage of the DBAPI ``setinputsizes()`` call. The purpose of this call is to establish the datatypes that are bound to a SQL statement for Python values being passed as parameters. While virtually no other DBAPI assigns any use to the ``setinputsizes()`` call, the cx_Oracle DBAPI relies upon it heavily in its interactions with the Oracle client interface, and in some scenarios it is not possible for SQLAlchemy to know exactly how data should be bound, as some settings can cause profoundly different performance characteristics, while altering the type coercion behavior at the same time. Users of the cx_Oracle dialect are **strongly encouraged** to read through cx_Oracle's list of built-in datatype symbols at https://cx-oracle.readthedocs.io/en/latest/api_manual/module.html#database-types. Note that in some cases, significant performance degradation can occur when using these types vs. not, in particular when specifying ``cx_Oracle.CLOB``. On the SQLAlchemy side, the :meth:`.DialectEvents.do_setinputsizes` event can be used both for runtime visibility (e.g. logging) of the setinputsizes step as well as to fully control how ``setinputsizes()`` is used on a per-statement basis. .. versionadded:: 1.2.9 Added :meth:`.DialectEvents.setinputsizes` Example 1 - logging all setinputsizes calls ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ The following example illustrates how to log the intermediary values from a SQLAlchemy perspective before they are converted to the raw ``setinputsizes()`` parameter dictionary. The keys of the dictionary are :class:`.BindParameter` objects which have a ``.key`` and a ``.type`` attribute:: from sqlalchemy import create_engine, event engine = create_engine("oracle+cx_oracle://scott:tiger@host/xe") @event.listens_for(engine, "do_setinputsizes") def _log_setinputsizes(inputsizes, cursor, statement, parameters, context): for bindparam, dbapitype in inputsizes.items(): log.info( "Bound parameter name: %s SQLAlchemy type: %r " "DBAPI object: %s", bindparam.key, bindparam.type, dbapitype) Example 2 - remove all bindings to CLOB ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ The ``CLOB`` datatype in cx_Oracle incurs a significant performance overhead, however is set by default for the ``Text`` type within the SQLAlchemy 1.2 series. This setting can be modified as follows:: from sqlalchemy import create_engine, event from cx_Oracle import CLOB engine = create_engine("oracle+cx_oracle://scott:tiger@host/xe") @event.listens_for(engine, "do_setinputsizes") def _remove_clob(inputsizes, cursor, statement, parameters, context): for bindparam, dbapitype in list(inputsizes.items()): if dbapitype is CLOB: del inputsizes[bindparam] .. _cx_oracle_returning: RETURNING Support ----------------- The cx_Oracle dialect implements RETURNING using OUT parameters. The dialect supports RETURNING fully. .. _cx_oracle_lob: LOB Datatypes -------------- LOB datatypes refer to the "large object" datatypes such as CLOB, NCLOB and BLOB. Modern versions of cx_Oracle and oracledb are optimized for these datatypes to be delivered as a single buffer. As such, SQLAlchemy makes use of these newer type handlers by default. To disable the use of newer type handlers and deliver LOB objects as classic buffered objects with a ``read()`` method, the parameter ``auto_convert_lobs=False`` may be passed to :func:`_sa.create_engine`, which takes place only engine-wide. Two Phase Transactions Not Supported ------------------------------------- Two phase transactions are **not supported** under cx_Oracle due to poor driver support. As of cx_Oracle 6.0b1, the interface for two phase transactions has been changed to be more of a direct pass-through to the underlying OCI layer with less automation. The additional logic to support this system is not implemented in SQLAlchemy. .. _cx_oracle_numeric: Precision Numerics ------------------ SQLAlchemy's numeric types can handle receiving and returning values as Python ``Decimal`` objects or float objects. When a :class:`.Numeric` object, or a subclass such as :class:`.Float`, :class:`_oracle.DOUBLE_PRECISION` etc. is in use, the :paramref:`.Numeric.asdecimal` flag determines if values should be coerced to ``Decimal`` upon return, or returned as float objects. To make matters more complicated under Oracle, Oracle's ``NUMBER`` type can also represent integer values if the "scale" is zero, so the Oracle-specific :class:`_oracle.NUMBER` type takes this into account as well. The cx_Oracle dialect makes extensive use of connection- and cursor-level "outputtypehandler" callables in order to coerce numeric values as requested. These callables are specific to the specific flavor of :class:`.Numeric` in use, as well as if no SQLAlchemy typing objects are present. There are observed scenarios where Oracle may sends incomplete or ambiguous information about the numeric types being returned, such as a query where the numeric types are buried under multiple levels of subquery. The type handlers do their best to make the right decision in all cases, deferring to the underlying cx_Oracle DBAPI for all those cases where the driver can make the best decision. When no typing objects are present, as when executing plain SQL strings, a default "outputtypehandler" is present which will generally return numeric values which specify precision and scale as Python ``Decimal`` objects. To disable this coercion to decimal for performance reasons, pass the flag ``coerce_to_decimal=False`` to :func:`_sa.create_engine`:: engine = create_engine("oracle+cx_oracle://dsn", coerce_to_decimal=False) The ``coerce_to_decimal`` flag only impacts the results of plain string SQL statements that are not otherwise associated with a :class:`.Numeric` SQLAlchemy type (or a subclass of such). .. versionchanged:: 1.2 The numeric handling system for cx_Oracle has been reworked to take advantage of newer cx_Oracle features as well as better integration of outputtypehandlers.