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https://github.com/sqlalchemy/alembic

A database migrations tool for SQLAlchemy.
https://github.com/sqlalchemy/alembic

python sql sqlalchemy

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A database migrations tool for SQLAlchemy.

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README 

        
Alembic is a database migrations tool written by the author

of `SQLAlchemy `_.  A migrations tool

offers the following functionality:



* Can emit ALTER statements to a database in order to change

  the structure of tables and other constructs

* Provides a system whereby "migration scripts" may be constructed;

  each script indicates a particular series of steps that can "upgrade" a

  target database to a new version, and optionally a series of steps that can

  "downgrade" similarly, doing the same steps in reverse.

* Allows the scripts to execute in some sequential manner.



The goals of Alembic are:



* Very open ended and transparent configuration and operation.   A new

  Alembic environment is generated from a set of templates which is selected

  among a set of options when setup first occurs. The templates then deposit a

  series of scripts that define fully how database connectivity is established

  and how migration scripts are invoked; the migration scripts themselves are

  generated from a template within that series of scripts. The scripts can

  then be further customized to define exactly how databases will be

  interacted with and what structure new migration files should take.

* Full support for transactional DDL.   The default scripts ensure that all

  migrations occur within a transaction - for those databases which support

  this (Postgresql, Microsoft SQL Server), migrations can be tested with no

  need to manually undo changes upon failure.

* Minimalist script construction.  Basic operations like renaming

  tables/columns, adding/removing columns, changing column attributes can be

  performed through one line commands like alter_column(), rename_table(),

  add_constraint(). There is no need to recreate full SQLAlchemy Table

  structures for simple operations like these - the functions themselves

  generate minimalist schema structures behind the scenes to achieve the given

  DDL sequence.

* "auto generation" of migrations. While real world migrations are far more

  complex than what can be automatically determined, Alembic can still

  eliminate the initial grunt work in generating new migration directives

  from an altered schema.  The ``--autogenerate`` feature will inspect the

  current status of a database using SQLAlchemy's schema inspection

  capabilities, compare it to the current state of the database model as

  specified in Python, and generate a series of "candidate" migrations,

  rendering them into a new migration script as Python directives. The

  developer then edits the new file, adding additional directives and data

  migrations as needed, to produce a finished migration. Table and column

  level changes can be detected, with constraints and indexes to follow as

  well.

* Full support for migrations generated as SQL scripts.   Those of us who

  work in corporate environments know that direct access to DDL commands on a

  production database is a rare privilege, and DBAs want textual SQL scripts.

  Alembic's usage model and commands are oriented towards being able to run a

  series of migrations into a textual output file as easily as it runs them

  directly to a database. Care must be taken in this mode to not invoke other

  operations that rely upon in-memory SELECTs of rows - Alembic tries to

  provide helper constructs like bulk_insert() to help with data-oriented

  operations that are compatible with script-based DDL.

* Non-linear, dependency-graph versioning.   Scripts are given UUID

  identifiers similarly to a DVCS, and the linkage of one script to the next

  is achieved via human-editable markers within the scripts themselves.

  The structure of a set of migration files is considered as a

  directed-acyclic graph, meaning any migration file can be dependent

  on any other arbitrary set of migration files, or none at

  all.  Through this open-ended system, migration files can be organized

  into branches, multiple roots, and mergepoints, without restriction.

  Commands are provided to produce new branches, roots, and merges of

  branches automatically.

* Provide a library of ALTER constructs that can be used by any SQLAlchemy

  application. The DDL constructs build upon SQLAlchemy's own DDLElement base

  and can be used standalone by any application or script.

* At long last, bring SQLite and its inability to ALTER things into the fold,

  but in such a way that SQLite's very special workflow needs are accommodated

  in an explicit way that makes the most of a bad situation, through the

  concept of a "batch" migration, where multiple changes to a table can

  be batched together to form a series of instructions for a single, subsequent

  "move-and-copy" workflow.   You can even use "move-and-copy" workflow for

  other databases, if you want to recreate a table in the background

  on a busy system.



Documentation and status of Alembic is at https://alembic.sqlalchemy.org/



The SQLAlchemy Project

======================



Alembic is part of the `SQLAlchemy Project `_ and

adheres to the same standards and conventions as the core project.



Development / Bug reporting / Pull requests

___________________________________________



Please refer to the

`SQLAlchemy Community Guide `_ for

guidelines on coding and participating in this project.



Code of Conduct

_______________



Above all, SQLAlchemy places great emphasis on polite, thoughtful, and

constructive communication between users and developers.

Please see our current Code of Conduct at

`Code of Conduct `_.



License

=======



Alembic is distributed under the `MIT license

`_.