Peewee DB Evolve

Diffs your models against your database, and outputs SQL to (non-destructively) update your schema.

Think of it as db.create_tables() on steriods (which doesn't drop your database).

You can also think of it as schema migrations, without having to actually write the migrations.

Quick Start

1. Run: sudo pip install peewee-db-evolve
2. Add import peeweedbevolve anywhere before your models are defined.
3. Run db.evolve() where you would have normally run db.create_tables(), and enjoy!

Functions

The function evolve(db, interactive=True, ignore_tables=None, schema=None) is injected into Peewee's database object.

• interactive if true will display the proposed changes and prompt you to confirm. If false will apply them automatically.
• ignore_tables takes a list of tables you don't want to evolve for whatever reason.
• schema will evolve schemas other than your default schema.

Usage

Write your models as you normall would. This project will diff the schema defined by your models from the schema defined in your database, and offer schema changes for your approval.

Renaming columns can be achieved by using the aka keyword injected into Peewee's column definition. For example, if you have:

name = pw.CharField(null=True)

And you want to rename it to full_name, change your model definition to read:

full_name = pw.CharField(null=True, aka='name')

This will generate a RENAME operation instead of a delete then an add.

The parameter aka can be either a string or a list (if you have multiple previous names). Once it's evolved you can remove it or leave it as you see fit.

Example

See our Hello World example.

Supported Databases

• PostgreSQL
• MySQL

Frequently Asked Questions

Does this work with existing projects, or only with new projects?

This works very well with existing projects. If your API only works with new projects, you're probably doing it wrong.

Don't you give up control by not writing your own migrations?

Managing your schema by writing your own migrations is kind of like managing your source code by writing your own patch files in addition to writing your actual code. A well vetted diff tool is going to be better and faster at it than you.

How old / well vetted is this tool?

This project has been in production use since August 2016. (We switched to Peewee as an ORM.) But it's a style of schema management I've been using for ~10 years now.

How can I prevent peewee-db-evolve from evolving a specific table or class?

In the class' Meta class, add evolve = False and peewee-db-evolve will ignore it. If you don't have a class for a specific table, just make a do-nothing dummy class for it. Or you can pass in any iterable into the ignore_tables kwarg of evolve().

Tests

How to run:

$ python3 test.py
..................................................................................................
----------------------------------------------------------------------
Ran 110 tests in 49.408s

OK

If you get this:

EERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)

Something like this should get you going:

$ sudo apt install mysql-server
[...]

$ sudo cat /etc/mysql/debian.cnf
# Automatically generated for Debian scripts. DO NOT TOUCH!
[client]
host     = localhost
user     = debian-sys-maint
password = XXXXXXXXXXXXX
socket   = /var/run/mysqld/mysqld.sock

$ mysql -u debian-sys-maint -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
mysql> CREATE USER 'derek'@'localhost';
mysql> GRANT ALL ON *.* TO 'derek'@'localhost';
mysql> flush privileges;

Obviously change derek to your username.

WARNING: This creates an unauthenticated mysql user on your local box. Don't do this if you have anything important in your local MySQL instance!