140 lines
4.5 KiB
Python
140 lines
4.5 KiB
Python
# mssql/mxodbc.py
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# Copyright (C) 2005-2018 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+mxodbc
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:name: mxODBC
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:dbapi: mxodbc
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:connectstring: mssql+mxodbc://<username>:<password>@<dsnname>
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:url: http://www.egenix.com/
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Execution Modes
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---------------
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mxODBC features two styles of statement execution, using the
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``cursor.execute()`` and ``cursor.executedirect()`` methods (the second being
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an extension to the DBAPI specification). The former makes use of a particular
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API call specific to the SQL Server Native Client ODBC driver known
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SQLDescribeParam, while the latter does not.
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mxODBC apparently only makes repeated use of a single prepared statement
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when SQLDescribeParam is used. The advantage to prepared statement reuse is
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one of performance. The disadvantage is that SQLDescribeParam has a limited
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set of scenarios in which bind parameters are understood, including that they
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cannot be placed within the argument lists of function calls, anywhere outside
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the FROM, or even within subqueries within the FROM clause - making the usage
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of bind parameters within SELECT statements impossible for all but the most
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simplistic statements.
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For this reason, the mxODBC dialect uses the "native" mode by default only for
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INSERT, UPDATE, and DELETE statements, and uses the escaped string mode for
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all other statements.
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This behavior can be controlled via
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:meth:`~sqlalchemy.sql.expression.Executable.execution_options` using the
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``native_odbc_execute`` flag with a value of ``True`` or ``False``, where a
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value of ``True`` will unconditionally use native bind parameters and a value
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of ``False`` will unconditionally use string-escaped parameters.
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"""
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from ... import types as sqltypes
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from ...connectors.mxodbc import MxODBCConnector
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from .pyodbc import MSExecutionContext_pyodbc, _MSNumeric_pyodbc
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from .base import (MSDialect,
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MSSQLStrictCompiler,
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VARBINARY,
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_MSDateTime, _MSDate, _MSTime)
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class _MSNumeric_mxodbc(_MSNumeric_pyodbc):
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"""Include pyodbc's numeric processor.
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"""
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class _MSDate_mxodbc(_MSDate):
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def bind_processor(self, dialect):
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def process(value):
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if value is not None:
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return "%s-%s-%s" % (value.year, value.month, value.day)
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else:
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return None
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return process
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class _MSTime_mxodbc(_MSTime):
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def bind_processor(self, dialect):
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def process(value):
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if value is not None:
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return "%s:%s:%s" % (value.hour, value.minute, value.second)
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else:
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return None
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return process
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class _VARBINARY_mxodbc(VARBINARY):
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"""
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mxODBC Support for VARBINARY column types.
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This handles the special case for null VARBINARY values,
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which maps None values to the mx.ODBC.Manager.BinaryNull symbol.
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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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# should pull from mx.ODBC.Manager.BinaryNull
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return dialect.dbapi.BinaryNull
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return process
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class MSExecutionContext_mxodbc(MSExecutionContext_pyodbc):
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"""
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The pyodbc execution context is useful for enabling
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SELECT SCOPE_IDENTITY in cases where OUTPUT clause
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does not work (tables with insert triggers).
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"""
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# todo - investigate whether the pyodbc execution context
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# is really only being used in cases where OUTPUT
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# won't work.
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class MSDialect_mxodbc(MxODBCConnector, MSDialect):
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# this is only needed if "native ODBC" mode is used,
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# which is now disabled by default.
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# statement_compiler = MSSQLStrictCompiler
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execution_ctx_cls = MSExecutionContext_mxodbc
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# flag used by _MSNumeric_mxodbc
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_need_decimal_fix = True
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colspecs = {
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sqltypes.Numeric: _MSNumeric_mxodbc,
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sqltypes.DateTime: _MSDateTime,
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sqltypes.Date: _MSDate_mxodbc,
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sqltypes.Time: _MSTime_mxodbc,
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VARBINARY: _VARBINARY_mxodbc,
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sqltypes.LargeBinary: _VARBINARY_mxodbc,
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}
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def __init__(self, description_encoding=None, **params):
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super(MSDialect_mxodbc, self).__init__(**params)
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self.description_encoding = description_encoding
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dialect = MSDialect_mxodbc
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