Alembic - Database Management - Get started

Alembic is a powerful tool to manage database generating migrations and versions of tables, views and etc enabling a easy management of your database.

#Installing the alembicpip install alembic#starting the alembicalembic init alembic

Now you have to edit the alembic.ini and put your connectionstring using the field sqlalchemy.url

# A generic, single database configuration.[alembic]# path to migration scriptsscript_location = alembic# 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# 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.# (new in 1.5.5)prepend_sys_path = .# timezone to use when rendering the date within the migration file# as well as the filename.# If specified, requires the python-dateutil library that can be# installed by adding `alembic[tz]` to the pip requirements# string value is passed to dateutil.tz.gettz()# 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 ${script_location}/versions.  When using multiple version# directories, initial revisions must be specified with --version-path.# The path separator used here should be the separator specified by "version_path_separator" below.# version_locations = %(here)s/bar:%(here)s/bat:${script_location}/versions# version path separator; As mentioned above, this is the character used to split# version_locations. The default within new alembic.ini files is "os", which uses os.pathsep.# If this key is omitted entirely, it falls back to the legacy behavior of splitting on spaces and/or commas.# Valid values for version_path_separator are:## version_path_separator = :# version_path_separator = ;# version_path_separator = spaceversion_path_separator = os  # Use os.pathsep. Default configuration used for new projects.# the output encoding used when revision files# are written from script.py.mako# output_encoding = utf-8sqlalchemy.url = driver://user:pass@localhost/dbname# [post_write_hooks]# This section 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# Logging configuration[loggers]keys = root,sqlalchemy,alembic[handlers]keys = console[formatters]keys = generic[logger_root]level = WARNhandlers = consolequalname =[logger_sqlalchemy]level = WARNhandlers =qualname = sqlalchemy.engine[logger_alembic]level = INFOhandlers =qualname = alembic[handler_console]class = StreamHandlerargs = (sys.stderr,)level = NOTSETformatter = generic[formatter_generic]format = %(levelname)-5.5s [%(name)s] %(message)sdatefmt = %H:%M:%S

Now let’s create the first table definition

alembic revision -m "create account table"

He gonna create a migration file and you can edit it and put your table definition

"""create user tableRevision ID: Revises: Create Date: 2022-04-25 21:41:11.988502"""from alembic import opimport datetimeimport sqlalchemy as sa# revision identifiers, used by Alembic.revision = 'xxxxxx'down_revision = Nonebranch_labels = Nonedepends_on = Nonedef upgrade():    op.create_table(        'account',        sa.Column('id', sa.Integer, primary_key=True),        sa.Column('name', sa.String(128), nullable=False),        sa.Column('description', sa.Unicode(200)),        sa.Column('created', sa.DateTime, default=sa.func.now()),        sa.Column('updated', sa.DateTime, onupdate=sa.func.now()),    )  def downgrade():    op.drop_table('account')

Now let’s run it to create the table

alembic upgrade head

Voila, your table is created! Now lets edit this table adding a column

alembic revision -m "Add a column"

Now he created another migration file to edit and put your changes

"""Add a columnRevision ID: Revises: Create Date: 2022-04-26 23:16:56.501818"""from alembic import opimport sqlalchemy as sa# revision identifiers, used by Alembic.revision = 'xxxx'down_revision = 'yyy'branch_labels = Nonedepends_on = Nonedef upgrade():    op.add_column('account', sa.Column('birthdate', sa.DateTime))    op.add_column('account', sa.Column('email', sa.String(128)))    op.add_column('account', sa.Column('ip_source', sa.String(16)))    op.add_column('account', sa.Column('location', sa.String(128)))def downgrade():    op.drop_column('account', 'birthdate')    op.drop_column('account', 'email')    op.drop_column('account', 'ip_source')    op.drop_column('account', 'location')

Now let’s just run again and everything is voila!

alembic revision -m "Add a column"

Ref: Welcome to Alembic’s documentation! — Alembic 1.7.7 documentation (sqlalchemy.org)