Schema diff

Table of contents
  1. Schema diff
    1. Introduction
    2. Generating a migration
    3. What it detects
    4. Limitations

Introduction

Schema diff is the reverse of writing a migration by hand: you change your models and migro writes the migration. It resembles what Prisma and Django do with makemigrations.

Generating a migration

migro migration:diff [name] compares your GORM models with the live database and writes the difference as a new Go migration file. It treats every exported struct in app/models (MIGRO_MODELS_DIR) as a model; add // migro:ignore to a type’s doc comment to skip it.

migro migration:diff add_profile_fields
migro migration:diff --rename=users.name=full_name     # a rename, not a drop + add
migro migration:diff cleanup --allow-destructive       # include DROP COLUMN / DROP INDEX

The file uses the schema builder (t.String(...), t.Index(...)), so you can edit it before running migration:run. Behind it is migrate/diff, usable from code:

plan, err := diff.Generate(ctx, db, diff.Options{
    Renames: map[string]string{"users.name": "full_name"}, // otherwise a rename is a drop + add
}, &User{}, &Post{})

for _, w := range plan.Warnings { log.Println("warning:", w) }
for _, op := range plan.Blocked { log.Printf("not applied (destructive): %s %s", op.Kind, op.Table) }

path, err := plan.WriteGoFile("database/migrations", "migrations", "sync_models", time.Now()) // a Go migration; "" when there is nothing to do
paths, err := plan.WriteFiles("migrations", "sync_models")                                     // or .up.sql / .down.sql files

What it detects

What it detects: new tables, added/dropped/renamed columns, added/dropped indexes. Drops are listed in plan.Blocked and only written when Options{AllowDestructive: true}. It never drops tables.

Limitations

What it does not do: detect column type or nullability changes (some are reported as warnings), or translate default expressions (reported as warnings). The down file for a dropped column is a comment, because the data cannot be restored. Always read the generated SQL before applying it.