alembic: Allow cdr, config and voicemail to exist in the same schema

cdr, config and voicemail are all separate alembic trees.  Because
alembic's default is to use a table named 'alembic_version' to store
the current tree revision, the 3 trees can't exist in the same schema
without stepping on each other.

Now each tree uses 'alembic_version_<tree_name>' as the version table.
Each tree's env.py script now first checks for 'alembic_version'.  If
it finds it AND its revision is in the tree's history, the script
renames it to 'alembic_version_<tree_name>'.  Regardless, the script
then continues with the migration using 'alembic_version_<tree_name>'
and creates that table if it's not found.  The result is that if an
existing 'alembic_version' table was found but it didn't belong to this
tree, it's left alone and 'alembic_version_<tree_name>' is used or
created.

WARNING:  If multiple trees are using the same schema, they MUST NOT
CRU or D any objects with names that might exist in the other trees.
An example would be 'yesno_values' type.  If two trees perform
operations on it, one tree could pull it out from under the other.
Thankfully we currently don't share any names among cdr, config and
voicemail.

NOTE:  Since the env.py scripts in each tree were identical, a common
env.py has been placed in the ast-db-manage directory and a symlink
to it has been placed in each tree directory.

ASTERISK-24311 #close
Reported-by: Dafi Ni

Change-Id: I4d593f000350deb5d21a14fa1e9bc3896844d898

contrib/ast-db-manage/voicemail/env.py

@@ -1,74 +0,0 @@
-from __future__ import with_statement
-from alembic import context
-from sqlalchemy import engine_from_config, pool
-from logging.config import fileConfig
-
-# 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
-
-# add your model's MetaData object here
-# for 'autogenerate' support
-# from myapp import mymodel
-# target_metadata = mymodel.Base.metadata
-target_metadata = None
-
-# 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)
-
-    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)
-
-    connection = engine.connect()
-    context.configure(
-                connection=connection,
-                target_metadata=target_metadata
-                )
-
-    try:
-        with context.begin_transaction():
-            context.run_migrations()
-    finally:
-        connection.close()
-
-if context.is_offline_mode():
-    run_migrations_offline()
-else:
-    run_migrations_online()
-

contrib/ast-db-manage/voicemail/env.py

@@ -0,0 +1 @@
+../env.py