migrations/env.py

   1 from __future__ import with_statement
   2 from alembic import context
   3 from sqlalchemy import engine_from_config, pool
   4 from logging.config import fileConfig
   5 import logging
   6
   7 # this is the Alembic Config object, which provides
   8 # access to the values within the .ini file in use.
   9 config = context.config
  10
  11 # Interpret the config file for Python logging.
  12 # This line sets up loggers basically.
  13 fileConfig(config.config_file_name)
  14 logger = logging.getLogger('alembic.env')
  15
  16 # add your model's MetaData object here
  17 # for 'autogenerate' support
  18 # from myapp import mymodel
  19 # target_metadata = mymodel.Base.metadata
  20 from flask import current_app
  21 config.set_main_option('sqlalchemy.url',
  22                        current_app.config.get('SQLALCHEMY_DATABASE_URI'))
  23 target_metadata = current_app.extensions['migrate'].db.metadata
  24
  25 # other values from the config, defined by the needs of env.py,
  26 # can be acquired:
  27 # my_important_option = config.get_main_option("my_important_option")
  28 # ... etc.
  29
  30
  31 def run_migrations_offline():
  32     """Run migrations in 'offline' mode.
  33
  34     This configures the context with just a URL
  35     and not an Engine, though an Engine is acceptable
  36     here as well.  By skipping the Engine creation
  37     we don't even need a DBAPI to be available.
  38
  39     Calls to context.execute() here emit the given string to the
  40     script output.
  41
  42     """
  43     url = config.get_main_option("sqlalchemy.url")
  44     context.configure(url=url, compare_type=True)
  45
  46     with context.begin_transaction():
  47         context.run_migrations()
  48
  49
  50 def run_migrations_online():
  51     """Run migrations in 'online' mode.
  52
  53     In this scenario we need to create an Engine
  54     and associate a connection with the context.
  55
  56     """
  57
  58     # this callback is used to prevent an auto-migration from being generated
  59     # when there are no changes to the schema
  60     # reference: http://alembic.zzzcomputing.com/en/latest/cookbook.html
  61     def process_revision_directives(context, revision, directives):
  62         if getattr(config.cmd_opts, 'autogenerate', False):
  63             script = directives[0]
  64             if script.upgrade_ops.is_empty():
  65                 directives[:] = []
  66                 logger.info('No changes in schema detected.')
  67
  68     engine = engine_from_config(config.get_section(config.config_ini_section),
  69                                 prefix='sqlalchemy.',
  70                                 poolclass=pool.NullPool)
  71
  72     connection = engine.connect()
  73     context.configure(connection=connection,
  74                       target_metadata=target_metadata,
  75                       process_revision_directives=process_revision_directives,
  76                       compare_type=True,
  77                       **current_app.extensions['migrate'].configure_args)
  78
  79     try:
  80         with context.begin_transaction():
  81             context.run_migrations()
  82     finally:
  83         connection.close()
  84
  85 if context.is_offline_mode():
  86     run_migrations_offline()
  87 else:
  88     run_migrations_online()