Issue #1414 new

have dialect-specific TypeEngines support tranferrence between backends (reflection / tometadata)

Anonymous created an issue


just tried to convert a SQL-Server-DB to SQLite using SQLAlchemy 0.5.3 / 0.5.4 and PyODBC 2.1.5 using the following code:

import sqlalchemy as sa

engine1 = sa.create_engine(connstr, encoding="utf-8", echo=True) # MSSql Server
engine2 = sa.create_engine(connstr2, encoding="utf-8", echo=True) # Sqlite db

meta1 = sa.MetaData(bind=engine1) # gives a deprecation warning (see below)
meta2 = sa.MetaData(bind=engine2)

meta1.reflect() # takes a while but works well

for table in meta1.tables.values():

# no (real) complaints so far
# but this one makes some trouble

Deprecation Warning

C:\Python26\lib\site-packages\sqlalchemy\databases\ DeprecationWar
ning: object.__new__() takes no parameters
  return super(MSSQLDialect, cls).__new__(cls, *args, **kwargs)

Traceback thrown by create_all()

see attached file

Comments (3)

  1. Mike Bayer repo owner

    as yet we have never tried to support the use case of transferring types between backends. For the case here, it would be possible, although for most non-trivial cases it would not, for such types as PG's INTERVAL, UUID or MySQL's BIT type. The work involved would require TypeEngine objects that are specific to some database to specify a "fallback" type when being converted to some other engine...or perhaps this can be automated within TypeEngine.dialect_impl() (that may make this easier than the "2 day" severity given).

    there's been a major refactoring of types in 0.6 so any big changes like this are targeted there. of particular interest is the fact that 0.6 will in many cases rely upon the generic types (i.e. String, DateTime) a lot more than the DB-specific ones, which have been greatly reduced (although not for MS and MySQL, whose types have tons of DB-specific options).

    as a workaround for now you might want to iterate through the columns of your reflected Table objects and change them to be "generic" types, i.e. MSString becomes String, etc.

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