Developer Troubleshooting Guide

This guide is intended to provide information on how to resolve common problems encountered when developing code for magnum.

Troubleshooting MySQL

When creating alembic migrations, developers might encounter the Multiple head revisions are present for given argument 'head' error.

This can occur when two migrations revise the same head. For example, the developer creates a migration locally but another migration has already been accepted and merged into master that revises the same head:

$ alembic heads
12345 (your local head)
67890 (new master head)

In order to fix this, the developer should update the down_revision of their local migration to point to the head of the new migration in master:

# revision identifiers, used by Alembic.
revision = '12345'
down_revision = '67890'

Now the newest local migration should be head:

$ alembic heads
12345 (your local head)