266 lines
9.3 KiB
Python
266 lines
9.3 KiB
Python
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# mssql/pyodbc.py
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# Copyright (C) 2005-2015 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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"""
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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-based connection is **preferred** overall when using ODBC. A
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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 **not preferred**, however are supported.
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The ODBC driver name must be explicitly specified::
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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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.. versionchanged:: 1.0.0 Hostname-based PyODBC connections now require the
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SQL Server driver name specified explicitly. SQLAlchemy cannot
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choose an optimal default here as it varies based on platform
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and installed drivers.
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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 exactly as specified in
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`ConnectionStrings <https://code.google.com/p/pyodbc/wiki/ConnectionStrings>`_
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into the driver using the parameter ``odbc_connect``. The delimeters must be URL escaped, however,
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as illustrated below using ``urllib.quote_plus``::
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import urllib
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params = urllib.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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Unicode Binds
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-------------
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The current state of PyODBC on a unix backend with FreeTDS and/or
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EasySoft is poor regarding unicode; different OS platforms and versions of
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UnixODBC versus IODBC versus FreeTDS/EasySoft versus PyODBC itself
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dramatically alter how strings are received. The PyODBC dialect attempts to
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use all the information it knows to determine whether or not a Python unicode
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literal can be passed directly to the PyODBC driver or not; while SQLAlchemy
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can encode these to bytestrings first, some users have reported that PyODBC
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mis-handles bytestrings for certain encodings and requires a Python unicode
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object, while the author has observed widespread cases where a Python unicode
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is completely misinterpreted by PyODBC, particularly when dealing with
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the information schema tables used in table reflection, and the value
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must first be encoded to a bytestring.
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It is for this reason that whether or not unicode literals for bound
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parameters be sent to PyODBC can be controlled using the
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``supports_unicode_binds`` parameter to ``create_engine()``. When
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left at its default of ``None``, the PyODBC dialect will use its
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best guess as to whether or not the driver deals with unicode literals
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well. When ``False``, unicode literals will be encoded first, and when
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``True`` unicode literals will be passed straight through. This is an interim
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flag that hopefully should not be needed when the unicode situation stabilizes
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for unix + PyODBC.
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.. versionadded:: 0.7.7
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``supports_unicode_binds`` parameter to ``create_engine()``\ .
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"""
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from .base import MSExecutionContext, MSDialect, VARBINARY
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from ...connectors.pyodbc import PyODBCConnector
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from ... import types as sqltypes, util
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import decimal
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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).\
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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 \
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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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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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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(
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[str(s) for s in _int][0:value.adjusted() + 1]),
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"".join(
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[str(s) for s in _int][value.adjusted() + 1:]))
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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(
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[str(s) for s in _int][0:value.adjusted() + 1]))
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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 _VARBINARY_pyodbc(VARBINARY):
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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 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 self._select_lastrowid and \
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self.dialect.use_scope_identity and \
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len(self.parameters[0]):
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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 as e:
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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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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__(self, description_encoding=None, **params):
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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 = self.use_scope_identity and \
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self.dbapi and \
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hasattr(self.dbapi.Cursor, 'nextset')
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self._need_decimal_fix = self.dbapi and \
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self._dbapi_version() < (2, 1, 8)
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dialect = MSDialect_pyodbc
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