Metadata-Version: 2.1
Name: automig
Version: 0.0.14
Summary: Declarative, automatic db migrations using SQL & git as the source of truth
Home-page: https://github.com/abe-winter/automigrate
Author: Abe Winter
License: UNKNOWN
Description: # automigrate
        
        Tool to diff SQL schemas in git and apply the migrations.
        
        Use this if you don't like to manage migrations separately from your declarative schema definitions.
        
        * [Warning this is beta software](#beta-software)
        * [Features](#features)
        * [Installation & basic use](#installation--basic-use)
        * [What's happening under the covers](#whats-happening-under-the-covers)
        * [What does & doesn't work](#what-does--doesnt-work)
        * [Comparison vs other tools](#comparison-vs-other-tools)
        * [Using with ORMs](#using-with-orms)
        * [Integrating with CI](#integrating-with-ci)
        
        ## Beta software
        
        This is beta software and you should be careful with its output.
        
        * Eyeball the migrations before applying them
        * Proactively raise github issues for things that seem broken
        
        ## Features
        
        * Operates on `*.sql` files (i.e. files with `create table` and `create index` statements)
        * Operates on git -- meaning that it tracks the git version of applied migration and can create a SQL migration given two git refs
        * Outputs migrations as SQL
        * No need to write or store migrations for simple cases -- they're defined bidirectionally in terms of your git history
        * Ability to specify migrations manually when needed
        * Stores the history of applied migrations in sql in `automigrate_meta` table
        
        ## Philosophy
        
        * Defining your schema in your ORM is nuts because it ties you to one language, reduces clarity, and sometimes limits SQL features you can use
        * Existing migration tools don't pull their weight
        * SQL is a more general skill than ORMs and other tools should therefore mirror SQL
        * Mirroring live databases to get a schema is insane because are you tunneling to prod to run your linter? Live DB shouldn't be available to developers. Source of truth should be git.
        * Schema should be versioned using the same git shas as code so the logic is easy to detect if a deploy requires a migration
        
        ## Installation & basic use
        
        To install, `pip install automig` (or use `pip3` if that fails). This should install dependencies and register the automig command.
        
        You can fall back to `git+https://github.com/abe-winter/automigrate` if you want latest master.
        
        Typical invocations:
        
        ```bash
        # create an initial migration (also create meta tables)
        automig 218dd2c 'test/schema/*.sql' --initial | psql -h 172.17.0.2 -U postgres --single-transaction
        
        # migrate a database
        LAST_SHA=$(psql -h 172.17.0.2 -U postgres -t -c "select sha from automigrate_meta order by id desc limit 1")
        echo migrating from $LAST_SHA
        automig $LAST_SHA...b5b40ce 'test/schema/*.sql' | psql -h 172.17.0.2 -U postgres --single-transaction
        
        # I guess you can just migrate to HEAD if you're feeling lucky
        automig $LAST_SHA...HEAD 'test/schema/*.sql' | psql -h 172.17.0.2 -U postgres --single-transaction
        ```
        
        ## What's happening under the covers
        
        Nothing fancy. When you run `automig 218dd2c...b5b40ce 'test/schema/*.sql'` (these are real SHAs in this git repo and will work if you clone the repo), it outputs:
        
        ```sql
        -- changeset created from Namespace(glob='test/schema/*.sql', initial=False, opaque=False, ref='218dd2c...b5b40ce', update_meta=False) at 2019-09-26 01:57:58.404722
        -- changes for 9dcbd4e.t1
        alter table t1 add column b int;
        -- changes for b5b40ce.t1
        create index t1a on t1 (a);
        -- changes for b5b40ce.t2
        create table t2 (a int primary key);
        insert into automigrate_meta (fromsha, sha, automig_version, opaque) values ('218dd2c', '9dcbd4e81e9a0dd7629ed7ae82a86891a88f76f3', '0.0.10', false);
        insert into automigrate_meta (fromsha, sha, automig_version, opaque) values ('9dcbd4e81e9a0dd7629ed7ae82a86891a88f76f3', 'b5b40ce718ea7241fee8d0a3826f244d21bf413c', '0.0.10', false);
        ```
        
        ## What does & doesn't work
        
        * [x] Adding tables, indexes and columns should mostly work
        * [x] drop column works
        * [x] modifying columns partially works, supports changes to types, defaults, nullable. Read the `diff_column()` function for up-to-date information and file bugs for specific holes.
        * [x] add, drop and change primary keys
        * [x] For diffs that are erroring, you can override with a [.manualmig.yml file](./.manualmig.yml)
        * [ ] not sure if postgres 'partition by' is supported but the differ will become very upset if you change it
        * [ ] Be careful with using unescaped keywords as names (i.e. a table named table) -- you'll likely confuse the parser even where your sql engine allows it
        * [ ] This hasn't been tested on a wide range of syntax (i.e. arrays / json)
        * [ ] Not sure if capitalized SQL keywords are supported (todo add tests)
        * [ ] Need a way to check live schema against desired to call out problems
        * undo, i.e. what would be 'down' in a typical migration tool.
          - [ ] This may work out of the box (pass `HEAD...HEAD~1` instead of `HEAD~1...HEAD`), but needs tests
          - [ ] up/down sections in .manualmig.yml
        * documentation for:
          - [ ] writing schema files
          - [ ] creating an initial migration
          - [ ] checklist for running migrations: determining last sha, inspecting migration, running migration (postgres / mysql)
          - [ ] resolving a rebase
          - [ ] troubleshoot and resolve `automigrate_meta` errors
          - [ ] using manualmig when the tool is confused
        * [x] `--opaque` flag to repair non-linear git history (i.e. rebase)
        
        ## Burndown
        
        * [ ] [0.2.0] integration test with mysql and postgres
        * [ ] [0.2.0] take more than one glob
        * [ ] [0.2.0] support 'create extension'
        * [ ] [0.2.0] support enums
        
        ## Comparison vs other tools
        
        * [prisma lift](https://github.com/prisma/lift) has a declarative schema which *isn't* sql but looks kind of like it, and depends on a runtime DB to generate the migration diff, but seems like a neat tool
        * [alembic](https://alembic.sqlalchemy.org/en/latest/tutorial.html), as far as I can tell, requires you to generate a skeleton python file for each change then fill it in yourself
        * [sqlite sqldiff.exe](https://www.sqlite.org/sqldiff.html) can diff schemas but operates on full sqlite databases and I'm not sure if it outputs DDL
        * liquibase might have a [diffing system](https://www.liquibase.org/documentation/diff.html) but from the docs it looks like it's outputting XML. And [they advise you not to use it](http://www.liquibase.org/2007/06/the-problem-with-database-diffs.html)
        * [redgate sql compare](https://documentation.red-gate.com/sc/sql-server-management-studio-add-in/getting-started-with-the-add-in) seems to support comparing 'create table' schemas across git versions, although it looks like you have to find the SHAs by hand in a GUI
        * [migra](https://github.com/djrobstep/migra) seems to require two live DBs to run a diff (one with current schema, one with new)
        * [sqitch](https://sqitch.org) seems to require manually specifying `deploy` sql (and optionally `revert` & `verify`)
        
        ## Using with ORMs
        
        Your ORM has to be willing to import a schema from create table statements. (I don't know any ORM that does this out of the box, although some can reflect a live DB, like [sqlalchemy's automap](https://docs.sqlalchemy.org/en/latest/orm/extensions/automap.html)).
        
        This repo contains a barebones, mostly untested harness to [generate sqlalchemy models from create table statements](./automig/lib/sa_harness.py). You can run it with:
        
        ```bash
        python -m automig.lib.sa_harness 'test/schema/*.sql'
        ```
        
        Happy to accept PRs to generate ORM defs from `create table` stmts (or vice versa).
        
        ## Integrating with CI
        
        This is how I would apply migrations in CI if I had a few weeks off to build tooling. If you try this & it works, let me know.
        
        * Flag the migration in your code review tool before merging the change to master
          - Ideally the CR tool would run automig against master branch and show automig's output so the reviewer can sign off
          - [terraform's version of this](https://www.terraform.io/docs/github-actions/index.html) is not a bad template to borrow
        * Detect that a migration needs to be applied when deploying
          - This means that your deploy bot needs to have access to your prod DB
          - For continuous automatic deployment setups, you may want to block auto deploy for and require explicit signoff for deploys which require a migration
          - Alert / page in the appropriate place when a deploy is held because it has a migration
        * Apply the migration from deploy CI
          - To be safe, this requires an exactly-once semantic
          - Unlock the automatic deployment when the migration has successfully applied
          - Alert / page on error applying
          - Some migrations may require downtime for part or all of your cluster -- these migrations probably won't be automatic
          - Note that the order of new code & migration depends on the contents of the migration. [This staffjoy post](https://blog.staffjoy.com/dont-migrate-databases-automatically-5039ab061365?gi=3451f6178158#5822) points out that with ORMs that select all columns, `add column` & `drop column` can both be done with 0 downtime, but drop column migrations must be applied **after** the new code is out
        
        ## Development workflow
        
        ```bash
        # enable .envrc with `direnv allow` if necessary, or set up your own virtualenv
        # pip install -r requirements.txt
        pip install pytest
        pytest # in repo root
        ```
        
        If you want to pitch in on the project, there are a bunch of `@pytest.mark.skip` tests that need to be filled in (most require feature development to get them passing).
        
Keywords: sql,migration,git,diff
Platform: UNKNOWN
Requires-Python: >=3.6
Description-Content-Type: text/markdown
