Hi all,
the company I worked for has decided to change a RDBMS behind our ERP.
The side effect of this is that the columns will no longer be prefixed with
*t$*
but with* t_* instead. I do not want to change all the occurences of column
names in my code. I should also mention, that I use only selects, and no
ORM.
So what I did was I made a new dialect as a subclass of mssql.pyodbc and
I overrode execution context and statement compiler. In statement
compiler's
visit_select I simply replace "t$" with "t_" in the select returned from
the parent,
and in execution context's get_result_proxy I return a proxy whose row
proxy's
keymap is slightly updated (don't worry, I am attaching the code).
My question: Is this the right way to do it?
Thanks in advance
--
Petr
( attaching the code of the dialect - same as this:
https://gist.github.com/4058539 )
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import copy
import sqlalchemy.engine.base
import sqlalchemy.dialects.mssql.base
import sqlalchemy.dialects.mssql.pyodbc
class SQLABaanRowProxy(sqlalchemy.engine.base.RowProxy):
def __init__(self, parent, row, processors, keymap):
"""
For all keys starting with "t_" adds also a "t$..." key.
"""
km = copy.deepcopy(keymap)
for (k, v) in keymap.iteritems():
if isinstance(k, basestring):
if k.startswith("t_"):
km["t$" + k[2:]] = v
super(SQLABaanRowProxy, self).__init__(parent, row, processors, km)
class SQLABaanResultProxy(sqlalchemy.engine.base.ResultProxy):
_process_row = SQLABaanRowProxy
class SQLABaanCompiler(sqlalchemy.dialects.mssql.base.MSSQLCompiler):
def visit_select(self, select, **kwargs):
"""
Brute-force replace of "t$" to "t_...":w
"""
ret = super(SQLABaanCompiler, self).visit_select(select, **kwargs)
ret = ret.replace("t$", "t_")
return ret
class SQLABaanExecutionContext(sqlalchemy.dialects.mssql.pyodbc.MSExecutionContext_pyodbc):
def get_result_proxy(self):
if self._result_proxy:
return self._result_proxy #can never happen as we do only selects
else:
return SQLABaanResultProxy(self)
class SQLABaan(sqlalchemy.dialects.mssql.pyodbc.MSDialect_pyodbc):
execution_ctx_cls = SQLABaanExecutionContext
statement_compiler = SQLABaanCompiler
dialect = SQLABaan
