376 lines
12 KiB
Python
376 lines
12 KiB
Python
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# mssql/pyodbc.py
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# Copyright (C) 2005-2019 the SQLAlchemy authors and contributors
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# <see AUTHORS file>
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#
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# This module is part of SQLAlchemy and is released under
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# the MIT License: http://www.opensource.org/licenses/mit-license.php
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r"""
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.. dialect:: mssql+pyodbc
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:name: PyODBC
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:dbapi: pyodbc
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:connectstring: mssql+pyodbc://<username>:<password>@<dsnname>
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:url: http://pypi.python.org/pypi/pyodbc/
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Connecting to PyODBC
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--------------------
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The URL here is to be translated to PyODBC connection strings, as
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detailed in `ConnectionStrings <https://code.google.com/p/pyodbc/wiki/ConnectionStrings>`_.
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DSN Connections
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^^^^^^^^^^^^^^^
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A DSN connection in ODBC means that a pre-existing ODBC datasource is
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configured on the client machine. The application then specifies the name
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of this datasource, which encompasses details such as the specific ODBC driver
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in use as well as the network address of the database. Assuming a datasource
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is configured on the client, a basic DSN-based connection looks like::
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engine = create_engine("mssql+pyodbc://scott:tiger@some_dsn")
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Which above, will pass the following connection string to PyODBC::
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dsn=mydsn;UID=user;PWD=pass
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If the username and password are omitted, the DSN form will also add
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the ``Trusted_Connection=yes`` directive to the ODBC string.
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Hostname Connections
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^^^^^^^^^^^^^^^^^^^^
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Hostname-based connections are also supported by pyodbc. These are often
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easier to use than a DSN and have the additional advantage that the specific
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database name to connect towards may be specified locally in the URL, rather
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than it being fixed as part of a datasource configuration.
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When using a hostname connection, the driver name must also be specified in the
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query parameters of the URL. As these names usually have spaces in them, the
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name must be URL encoded which means using plus signs for spaces::
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engine = create_engine("mssql+pyodbc://scott:tiger@myhost:port/databasename?driver=SQL+Server+Native+Client+10.0")
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Other keywords interpreted by the Pyodbc dialect to be passed to
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``pyodbc.connect()`` in both the DSN and hostname cases include:
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``odbc_autotranslate``, ``ansi``, ``unicode_results``, ``autocommit``.
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Pass through exact Pyodbc string
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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A PyODBC connection string can also be sent in pyodbc's format directly, as
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specified in `ConnectionStrings
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<https://code.google.com/p/pyodbc/wiki/ConnectionStrings>`_ into the driver
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using the parameter ``odbc_connect``. The delimeters must be URL encoded, as
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illustrated below using ``urllib.parse.quote_plus``::
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import urllib
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params = urllib.parse.quote_plus("DRIVER={SQL Server Native Client 10.0};SERVER=dagger;DATABASE=test;UID=user;PWD=password")
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engine = create_engine("mssql+pyodbc:///?odbc_connect=%s" % params)
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Driver / Unicode Support
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-------------------------
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PyODBC works best with Microsoft ODBC drivers, particularly in the area
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of Unicode support on both Python 2 and Python 3.
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Using the FreeTDS ODBC drivers on Linux or OSX with PyODBC is **not**
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recommended; there have been historically many Unicode-related issues
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in this area, including before Microsoft offered ODBC drivers for Linux
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and OSX. Now that Microsoft offers drivers for all platforms, for
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PyODBC support these are recommended. FreeTDS remains relevant for
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non-ODBC drivers such as pymssql where it works very well.
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Rowcount Support
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----------------
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Pyodbc only has partial support for rowcount. See the notes at
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:ref:`mssql_rowcount_versioning` for important notes when using ORM
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versioning.
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.. _mssql_pyodbc_fastexecutemany:
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Fast Executemany Mode
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---------------------
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The Pyodbc driver has added support for a "fast executemany" mode of execution
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which greatly reduces round trips for a DBAPI ``executemany()`` call when using
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Microsoft ODBC drivers. The feature is enabled by setting the flag
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``.fast_executemany`` on the DBAPI cursor when an executemany call is to be
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used. The SQLAlchemy pyodbc SQL Server dialect supports setting this flag
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automatically when the ``.fast_executemany`` flag is passed to
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:func:`.create_engine`; note that the ODBC driver must be the Microsoft driver
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in order to use this flag::
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engine = create_engine(
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"mssql+pyodbc://scott:tiger@mssql2017:1433/test?driver=ODBC+Driver+13+for+SQL+Server",
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fast_executemany=True)
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.. versionadded:: 1.3
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.. seealso::
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`fast executemany <https://github.com/mkleehammer/pyodbc/wiki/Features-beyond-the-DB-API#fast_executemany>`_
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- on github
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""" # noqa
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import decimal
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import re
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from .base import BINARY
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from .base import MSDialect
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from .base import MSExecutionContext
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from .base import VARBINARY
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from ... import exc
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from ... import types as sqltypes
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from ... import util
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from ...connectors.pyodbc import PyODBCConnector
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class _ms_numeric_pyodbc(object):
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"""Turns Decimals with adjusted() < 0 or > 7 into strings.
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The routines here are needed for older pyodbc versions
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as well as current mxODBC versions.
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"""
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def bind_processor(self, dialect):
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super_process = super(_ms_numeric_pyodbc, self).bind_processor(dialect)
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if not dialect._need_decimal_fix:
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return super_process
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def process(value):
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if self.asdecimal and isinstance(value, decimal.Decimal):
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adjusted = value.adjusted()
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if adjusted < 0:
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return self._small_dec_to_string(value)
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elif adjusted > 7:
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return self._large_dec_to_string(value)
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if super_process:
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return super_process(value)
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else:
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return value
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return process
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# these routines needed for older versions of pyodbc.
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# as of 2.1.8 this logic is integrated.
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def _small_dec_to_string(self, value):
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return "%s0.%s%s" % (
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(value < 0 and "-" or ""),
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"0" * (abs(value.adjusted()) - 1),
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"".join([str(nint) for nint in value.as_tuple()[1]]),
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)
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def _large_dec_to_string(self, value):
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_int = value.as_tuple()[1]
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if "E" in str(value):
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result = "%s%s%s" % (
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(value < 0 and "-" or ""),
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"".join([str(s) for s in _int]),
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"0" * (value.adjusted() - (len(_int) - 1)),
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)
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else:
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if (len(_int) - 1) > value.adjusted():
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result = "%s%s.%s" % (
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(value < 0 and "-" or ""),
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"".join([str(s) for s in _int][0 : value.adjusted() + 1]),
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"".join([str(s) for s in _int][value.adjusted() + 1 :]),
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)
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else:
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result = "%s%s" % (
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(value < 0 and "-" or ""),
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"".join([str(s) for s in _int][0 : value.adjusted() + 1]),
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)
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return result
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class _MSNumeric_pyodbc(_ms_numeric_pyodbc, sqltypes.Numeric):
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pass
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class _MSFloat_pyodbc(_ms_numeric_pyodbc, sqltypes.Float):
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pass
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class _ms_binary_pyodbc(object):
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"""Wraps binary values in dialect-specific Binary wrapper.
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If the value is null, return a pyodbc-specific BinaryNull
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object to prevent pyODBC [and FreeTDS] from defaulting binary
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NULL types to SQLWCHAR and causing implicit conversion errors.
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"""
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def bind_processor(self, dialect):
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if dialect.dbapi is None:
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return None
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DBAPIBinary = dialect.dbapi.Binary
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def process(value):
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if value is not None:
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return DBAPIBinary(value)
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else:
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# pyodbc-specific
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return dialect.dbapi.BinaryNull
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return process
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class _VARBINARY_pyodbc(_ms_binary_pyodbc, VARBINARY):
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pass
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class _BINARY_pyodbc(_ms_binary_pyodbc, BINARY):
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pass
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class MSExecutionContext_pyodbc(MSExecutionContext):
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_embedded_scope_identity = False
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def pre_exec(self):
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"""where appropriate, issue "select scope_identity()" in the same
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statement.
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Background on why "scope_identity()" is preferable to "@@identity":
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http://msdn.microsoft.com/en-us/library/ms190315.aspx
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Background on why we attempt to embed "scope_identity()" into the same
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statement as the INSERT:
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http://code.google.com/p/pyodbc/wiki/FAQs#How_do_I_retrieve_autogenerated/identity_values?
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"""
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super(MSExecutionContext_pyodbc, self).pre_exec()
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# don't embed the scope_identity select into an
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# "INSERT .. DEFAULT VALUES"
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if (
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self._select_lastrowid
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and self.dialect.use_scope_identity
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and len(self.parameters[0])
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):
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self._embedded_scope_identity = True
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self.statement += "; select scope_identity()"
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def post_exec(self):
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if self._embedded_scope_identity:
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# Fetch the last inserted id from the manipulated statement
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# We may have to skip over a number of result sets with
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# no data (due to triggers, etc.)
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while True:
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try:
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# fetchall() ensures the cursor is consumed
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# without closing it (FreeTDS particularly)
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row = self.cursor.fetchall()[0]
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break
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except self.dialect.dbapi.Error:
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# no way around this - nextset() consumes the previous set
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# so we need to just keep flipping
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self.cursor.nextset()
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self._lastrowid = int(row[0])
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else:
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super(MSExecutionContext_pyodbc, self).post_exec()
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class MSDialect_pyodbc(PyODBCConnector, MSDialect):
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execution_ctx_cls = MSExecutionContext_pyodbc
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colspecs = util.update_copy(
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MSDialect.colspecs,
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{
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sqltypes.Numeric: _MSNumeric_pyodbc,
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sqltypes.Float: _MSFloat_pyodbc,
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BINARY: _BINARY_pyodbc,
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# SQL Server dialect has a VARBINARY that is just to support
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# "deprecate_large_types" w/ VARBINARY(max), but also we must
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# handle the usual SQL standard VARBINARY
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VARBINARY: _VARBINARY_pyodbc,
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sqltypes.VARBINARY: _VARBINARY_pyodbc,
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sqltypes.LargeBinary: _VARBINARY_pyodbc,
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},
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)
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def __init__(
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self, description_encoding=None, fast_executemany=False, **params
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):
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if "description_encoding" in params:
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self.description_encoding = params.pop("description_encoding")
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super(MSDialect_pyodbc, self).__init__(**params)
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self.use_scope_identity = (
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self.use_scope_identity
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and self.dbapi
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and hasattr(self.dbapi.Cursor, "nextset")
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)
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self._need_decimal_fix = self.dbapi and self._dbapi_version() < (
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2,
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1,
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8,
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)
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self.fast_executemany = fast_executemany
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def _get_server_version_info(self, connection):
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try:
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# "Version of the instance of SQL Server, in the form
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# of 'major.minor.build.revision'"
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raw = connection.scalar(
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"SELECT CAST(SERVERPROPERTY('ProductVersion') AS VARCHAR)"
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)
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except exc.DBAPIError:
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# SQL Server docs indicate this function isn't present prior to
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# 2008. Before we had the VARCHAR cast above, pyodbc would also
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# fail on this query.
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return super(MSDialect_pyodbc, self)._get_server_version_info(
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connection, allow_chars=False
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)
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else:
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version = []
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r = re.compile(r"[.\-]")
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for n in r.split(raw):
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try:
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version.append(int(n))
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except ValueError:
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pass
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return tuple(version)
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def do_executemany(self, cursor, statement, parameters, context=None):
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if self.fast_executemany:
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cursor.fast_executemany = True
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super(MSDialect_pyodbc, self).do_executemany(
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cursor, statement, parameters, context=context
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)
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def is_disconnect(self, e, connection, cursor):
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if isinstance(e, self.dbapi.Error):
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for code in (
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"08S01",
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"01002",
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"08003",
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"08007",
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"08S02",
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"08001",
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"HYT00",
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"HY010",
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"10054",
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):
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if code in str(e):
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return True
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return super(MSDialect_pyodbc, self).is_disconnect(
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e, connection, cursor
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)
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dialect = MSDialect_pyodbc
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