migrations/env.py
from __future__ import with_statement
from alembic import context
from sqlalchemy import engine_from_config, pool
from logging.config import fileConfig
import logging
from alembic.operations import Operations, MigrateOperation
from flask import current_app
# 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.
fileConfig(config.config_file_name)
LOGGER = logging.getLogger('alembic.env')
# add your model's MetaData object here
# for 'autogenerate' support
# from myapp import mymodel
# target_metadata = mymodel.Base.metadata
config.set_main_option('sqlalchemy.url',
current_app.config.get('SQLALCHEMY_DATABASE_URI'))
target_metadata = current_app.extensions['migrate'].db.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.
# The below code is for running plpgsql(PSQL for postgres) stored procedures safely
# please refer alembic cookbook http://alembic.zzzcomputing.com/en/latest/cookbook.html
# for more
class ReversibleOp(MigrateOperation):
def __init__(self, target):
self.target = target
@classmethod
def invoke_for_target(cls, operations, target):
op = cls(target)
return operations.invoke(op)
def reverse(self):
raise NotImplementedError()
@classmethod
def _get_object_from_version(cls, operations, ident):
version, objname = ident.split(".")
module = operations.get_context().script.get_revision(version).module
obj = getattr(module, objname)
return obj
@classmethod
def replace(cls, operations, target, replaces=None, replace_with=None):
if replaces:
old_obj = cls._get_object_from_version(operations, replaces)
drop_old = cls(old_obj).reverse()
create_new = cls(target)
elif replace_with:
old_obj = cls._get_object_from_version(operations, replace_with)
drop_old = cls(target).reverse()
create_new = cls(old_obj)
else:
raise TypeError("replaces or replace_with is required")
operations.invoke(drop_old)
operations.invoke(create_new)
@Operations.register_operation("create_or_replace_sp", "invoke_for_target")
@Operations.register_operation("replace_sp", "replace")
class CreateSPOp(ReversibleOp):
def reverse(self):
return DropSPOp(self.target)
@Operations.register_operation("drop_sp", "invoke_for_target")
class DropSPOp(ReversibleOp):
def reverse(self):
return CreateSPOp(self.target)
@Operations.implementation_for(CreateSPOp)
def create_or_replace_sp(operations, operation):
operations.execute(
"CREATE OR REPLACE FUNCTION %s %s" % (
operation.target.name, operation.target.sqltext
)
)
@Operations.implementation_for(DropSPOp)
def drop_sp(operations, operation):
operations.execute("DROP FUNCTION %s" % operation.target.name)
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)
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.
"""
# this callback is used to prevent an auto-migration from being generated
# when there are no changes to the schema
# reference: http://alembic.readthedocs.org/en/latest/cookbook.html
def process_revision_directives(context, revision, directives):
if getattr(config.cmd_opts, 'autogenerate', False):
script = directives[0]
if script.upgrade_ops.is_empty():
directives[:] = []
LOGGER.info('No changes in schema detected.')
engine = engine_from_config(config.get_section(config.config_ini_section),
prefix='sqlalchemy.',
poolclass=pool.NullPool)
connection = engine.connect()
context.configure(connection=connection,
target_metadata=target_metadata,
process_revision_directives=process_revision_directives,
compare_type=True,
**current_app.extensions['migrate'].configure_args)
try:
with context.begin_transaction():
context.run_migrations()
finally:
connection.close()
if context.is_offline_mode():
run_migrations_offline()
else:
run_migrations_online()