env.py

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from __future__ import with_statement
from alembic import context
from alembic.script import ScriptDirectory
from alembic.operations import Operations
from sqlalchemy import engine_from_config, pool, MetaData
from sqlalchemy.ext.declarative import declarative_base
from logging.config import fileConfig
import logging

# this is the Alembic Config object, which provides
# access to the values within the .ini file in use.
config = context.config

# Interpret the config file for Python logging.
# This line sets up loggers basically.
try:
 fileConfig(config.config_file_name)
except:
 pass

## below block is needed for mssql
meta = MetaData(naming_convention = {
 "ix": 'ix_%(column_0_label)s',
 "uq": "uq_%(table_name)s_%(column_0_name)s",
 "ck": "ck_%(table_name)s_%(column_0_name)s_%(constraint_name)s",
 "fk": "fk_%(table_name)s_%(column_0_name)s_%(referred_table_name)s",
 "pk": "pk_%(table_name)s"
})
Base = declarative_base(metadata=meta)

logger = logging.getLogger('alembic.runtime.setup')
# add your model's MetaData object here
# for 'autogenerate' support
# from myapp import mymodel
# target_metadata = mymodel.Base.metadata
target_metadata = None
#Comment above line and uncomment below line for mssql
#target_metadata = Base.metadata

# other values from the config, defined by the needs of env.py,
# can be acquired:
# my_important_option = config.get_main_option("my_important_option")
# ... etc.

def run_migrations_offline():
 """Run migrations in 'offline' mode.

 This configures the context with just a URL
 and not an Engine, though an Engine is acceptable
 here as well. By skipping the Engine creation
 we don't even need a DBAPI to be available.

 Calls to context.execute() here emit the given string to the
 script output.

 """
 url = config.get_main_option("sqlalchemy.url")
 context.configure(url=url,target_metadata=target_metadata)

 with context.begin_transaction():
 context.run_migrations()

def run_migrations_online():
 """Run migrations in 'online' mode.

 In this scenario we need to create an Engine
 and associate a connection with the context.

 """
 engine = engine_from_config(
 config.get_section(config.config_ini_section),
 prefix='sqlalchemy.',
 poolclass=pool.NullPool)

 logger.info('Testing for an old alembic_version table.')

 connection = engine.connect()
 context.configure(
 connection=connection,
 target_metadata=target_metadata,
 version_table='alembic_version'
 )

 script_location = config.get_main_option('script_location')
 found = False
 mc = context.get_context()
 current_db_revision = mc.get_current_revision()
 script = ScriptDirectory.from_config(config)
 """ If there was an existing alembic_version table, we need to
 check that it's current revision is in the history for the tree
 we're working with.
 """
 for x in script.iterate_revisions('head', 'base'):
 if x.revision == current_db_revision:
 """ An alembic_versions table was found and it belongs to
 this alembic tree
 """
 logger.info(
 ('An old alembic_version table at revision %s was '
 'found for %s. Renaming to alembic_version_%s.'),
 current_db_revision, script_location,
 script_location)
 op = Operations(mc)
 try:
 with context.begin_transaction():
 op.rename_table(
 'alembic_version', 'alembic_version_%s'
 % script_location)
 found = True
 except:
 logger.error(('Unable to rename alembic_version to '
 'alembic_version_%s.'),
 script_location)
 connection.close()
 return

 break

 if not found:
 logger.info('Didn\'t find an old alembic_version table.')
 logger.info('Trying alembic_version_%s.' % script_location)

 """ We MAY have an alembic_version table that doesn't belong to
 this tree but if we still don't have an alembic_version_<tree>
 table, alembic will create it.
 """
 context.configure(
 connection=connection,
 target_metadata=target_metadata,
 version_table='alembic_version_' + script_location
 )
 mc = context.get_context()
 current_db_revision = mc.get_current_revision()
 if current_db_revision:
 logger.info(
 'Using the alembic_version_%s table at revision %s.',
 script_location, current_db_revision)
 else:
 logger.info('Creating new alembic_version_%s table.',
 script_location)

 try:
 with context.begin_transaction():
 context.run_migrations()
 finally:
 connection.close()


if context.is_offline_mode():
 run_migrations_offline()
else:
 run_migrations_online()