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venv/Lib/site-packages/alembic/templates/multidb/README

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+Rudimentary multi-database configuration.
+
+Multi-DB isn't vastly different from generic. The primary difference is that it
+will run the migrations N times (depending on how many databases you have
+configured), providing one engine name and associated context for each run.
+
+That engine name will then allow the migration to restrict what runs within it to
+just the appropriate migrations for that engine. You can see this behavior within
+the mako template.
+
+In the provided configuration, you'll need to have `databases` provided in
+alembic's config, and an `sqlalchemy.url` provided for each engine name.

venv/Lib/site-packages/alembic/templates/multidb/alembic.ini.mako

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+# a multi-database configuration.
+
+[alembic]
+# path to migration scripts.
+# this is typically a path given in POSIX (e.g. forward slashes)
+# format, relative to the token %(here)s which refers to the location of this
+# ini file
+script_location = ${script_location}
+
+# template used to generate migration file names; The default value is %%(rev)s_%%(slug)s
+# Uncomment the line below if you want the files to be prepended with date and time
+# see https://alembic.sqlalchemy.org/en/latest/tutorial.html#editing-the-ini-file
+# for all available tokens
+# file_template = %%(year)d_%%(month).2d_%%(day).2d_%%(hour).2d%%(minute).2d-%%(rev)s_%%(slug)s
+
+# sys.path path, will be prepended to sys.path if present.
+# defaults to the current working directory.  for multiple paths, the path separator
+# is defined by "path_separator" below.
+prepend_sys_path = .
+
+# timezone to use when rendering the date within the migration file
+# as well as the filename.
+# If specified, requires the python>=3.9 or backports.zoneinfo library and tzdata library.
+# Any required deps can installed by adding `alembic[tz]` to the pip requirements
+# string value is passed to ZoneInfo()
+# leave blank for localtime
+# timezone =
+
+# max length of characters to apply to the "slug" field
+# truncate_slug_length = 40
+
+# set to 'true' to run the environment during
+# the 'revision' command, regardless of autogenerate
+# revision_environment = false
+
+# set to 'true' to allow .pyc and .pyo files without
+# a source .py file to be detected as revisions in the
+# versions/ directory
+# sourceless = false
+
+# version location specification; This defaults
+# to <script_location>/versions.  When using multiple version
+# directories, initial revisions must be specified with --version-path.
+# The path separator used here should be the separator specified by "path_separator"
+# below.
+# version_locations = %(here)s/bar:%(here)s/bat:%(here)s/alembic/versions
+
+# path_separator; This indicates what character is used to split lists of file
+# paths, including version_locations and prepend_sys_path within configparser
+# files such as alembic.ini.
+# The default rendered in new alembic.ini files is "os", which uses os.pathsep
+# to provide os-dependent path splitting.
+#
+# Note that in order to support legacy alembic.ini files, this default does NOT
+# take place if path_separator is not present in alembic.ini.  If this
+# option is omitted entirely, fallback logic is as follows:
+#
+# 1. Parsing of the version_locations option falls back to using the legacy
+#    "version_path_separator" key, which if absent then falls back to the legacy
+#    behavior of splitting on spaces and/or commas.
+# 2. Parsing of the prepend_sys_path option falls back to the legacy
+#    behavior of splitting on spaces, commas, or colons.
+#
+# Valid values for path_separator are:
+#
+# path_separator = :
+# path_separator = ;
+# path_separator = space
+# path_separator = newline
+#
+# Use os.pathsep. Default configuration used for new projects.
+path_separator = os
+
+# set to 'true' to search source files recursively
+# in each "version_locations" directory
+# new in Alembic version 1.10
+# recursive_version_locations = false
+
+# the output encoding used when revision files
+# are written from script.py.mako
+# output_encoding = utf-8
+
+# for multiple database configuration, new named sections are added
+# which each include a distinct ``sqlalchemy.url`` entry.  A custom value
+# ``databases`` is added which indicates a listing of the per-database sections.
+# The ``databases`` entry as well as the URLs present in the ``[engine1]``
+# and ``[engine2]`` sections continue to be consumed by the user-maintained env.py
+# script only.
+
+databases = engine1, engine2
+
+[engine1]
+sqlalchemy.url = driver://user:pass@localhost/dbname
+
+[engine2]
+sqlalchemy.url = driver://user:pass@localhost/dbname2
+
+[post_write_hooks]
+# post_write_hooks defines scripts or Python functions that are run
+# on newly generated revision scripts.  See the documentation for further
+# detail and examples
+
+# format using "black" - use the console_scripts runner, against the "black" entrypoint
+# hooks = black
+# black.type = console_scripts
+# black.entrypoint = black
+# black.options = -l 79 REVISION_SCRIPT_FILENAME
+
+# lint with attempts to fix using "ruff" - use the module runner, against the "ruff" module
+# hooks = ruff
+# ruff.type = module
+# ruff.module = ruff
+# ruff.options = check --fix REVISION_SCRIPT_FILENAME
+
+# Alternatively, use the exec runner to execute a binary found on your PATH
+# hooks = ruff
+# ruff.type = exec
+# ruff.executable = ruff
+# ruff.options = check --fix REVISION_SCRIPT_FILENAME
+
+# Logging configuration.  This is also consumed by the user-maintained
+# env.py script only.
+[loggers]
+keys = root,sqlalchemy,alembic
+
+[handlers]
+keys = console
+
+[formatters]
+keys = generic
+
+[logger_root]
+level = WARNING
+handlers = console
+qualname =
+
+[logger_sqlalchemy]
+level = WARNING
+handlers =
+qualname = sqlalchemy.engine
+
+[logger_alembic]
+level = INFO
+handlers =
+qualname = alembic
+
+[handler_console]
+class = StreamHandler
+args = (sys.stderr,)
+level = NOTSET
+formatter = generic
+
+[formatter_generic]
+format = %(levelname)-5.5s [%(name)s] %(message)s
+datefmt = %H:%M:%S

venv/Lib/site-packages/alembic/templates/multidb/env.py

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+import logging
+from logging.config import fileConfig
+import re
+
+from sqlalchemy import engine_from_config
+from sqlalchemy import pool
+
+from alembic import context
+
+USE_TWOPHASE = False
+
+# 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.
+if config.config_file_name is not None:
+    fileConfig(config.config_file_name)
+logger = logging.getLogger("alembic.env")
+
+# gather section names referring to different
+# databases.  These are named "engine1", "engine2"
+# in the sample .ini file.
+db_names = config.get_main_option("databases", "")
+
+# add your model's MetaData objects here
+# for 'autogenerate' support.  These must be set
+# up to hold just those tables targeting a
+# particular database. table.tometadata() may be
+# helpful here in case a "copy" of
+# a MetaData is needed.
+# from myapp import mymodel
+# target_metadata = {
+#       'engine1':mymodel.metadata1,
+#       'engine2':mymodel.metadata2
+# }
+target_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() -> None:
+    """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.
+
+    """
+    # for the --sql use case, run migrations for each URL into
+    # individual files.
+
+    engines = {}
+    for name in re.split(r",\s*", db_names):
+        engines[name] = rec = {}
+        rec["url"] = context.config.get_section_option(name, "sqlalchemy.url")
+
+    for name, rec in engines.items():
+        logger.info("Migrating database %s" % name)
+        file_ = "%s.sql" % name
+        logger.info("Writing output to %s" % file_)
+        with open(file_, "w") as buffer:
+            context.configure(
+                url=rec["url"],
+                output_buffer=buffer,
+                target_metadata=target_metadata.get(name),
+                literal_binds=True,
+                dialect_opts={"paramstyle": "named"},
+            )
+            with context.begin_transaction():
+                context.run_migrations(engine_name=name)
+
+
+def run_migrations_online() -> None:
+    """Run migrations in 'online' mode.
+
+    In this scenario we need to create an Engine
+    and associate a connection with the context.
+
+    """
+
+    # for the direct-to-DB use case, start a transaction on all
+    # engines, then run all migrations, then commit all transactions.
+
+    engines = {}
+    for name in re.split(r",\s*", db_names):
+        engines[name] = rec = {}
+        rec["engine"] = engine_from_config(
+            context.config.get_section(name, {}),
+            prefix="sqlalchemy.",
+            poolclass=pool.NullPool,
+        )
+
+    for name, rec in engines.items():
+        engine = rec["engine"]
+        rec["connection"] = conn = engine.connect()
+
+        if USE_TWOPHASE:
+            rec["transaction"] = conn.begin_twophase()
+        else:
+            rec["transaction"] = conn.begin()
+
+    try:
+        for name, rec in engines.items():
+            logger.info("Migrating database %s" % name)
+            context.configure(
+                connection=rec["connection"],
+                upgrade_token="%s_upgrades" % name,
+                downgrade_token="%s_downgrades" % name,
+                target_metadata=target_metadata.get(name),
+            )
+            context.run_migrations(engine_name=name)
+
+        if USE_TWOPHASE:
+            for rec in engines.values():
+                rec["transaction"].prepare()
+
+        for rec in engines.values():
+            rec["transaction"].commit()
+    except:
+        for rec in engines.values():
+            rec["transaction"].rollback()
+        raise
+    finally:
+        for rec in engines.values():
+            rec["connection"].close()
+
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    run_migrations_online()

venv/Lib/site-packages/alembic/templates/multidb/script.py.mako

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+<%!
+import re
+
+%>"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+${imports if imports else ""}
+
+# revision identifiers, used by Alembic.
+revision: str = ${repr(up_revision)}
+down_revision: Union[str, Sequence[str], None] = ${repr(down_revision)}
+branch_labels: Union[str, Sequence[str], None] = ${repr(branch_labels)}
+depends_on: Union[str, Sequence[str], None] = ${repr(depends_on)}
+
+
+def upgrade(engine_name: str) -> None:
+    """Upgrade schema."""
+    globals()["upgrade_%s" % engine_name]()
+
+
+def downgrade(engine_name: str) -> None:
+    """Downgrade schema."""
+    globals()["downgrade_%s" % engine_name]()
+
+<%
+    db_names = config.get_main_option("databases")
+%>
+
+## generate an "upgrade_<xyz>() / downgrade_<xyz>()" function
+## for each database name in the ini file.
+
+% for db_name in re.split(r',\s*', db_names):
+
+def upgrade_${db_name}() -> None:
+    """Upgrade ${db_name} schema."""
+    ${context.get("%s_upgrades" % db_name, "pass")}
+
+
+def downgrade_${db_name}() -> None:
+    """Downgrade ${db_name} schema."""
+    ${context.get("%s_downgrades" % db_name, "pass")}
+
+% endfor