Fix Migration Error in Rails

Rails Migration Errors

Rails migrations fail for various reasons — database connection issues, conflicting schema changes, or migrations that aren't reversible. Here's how to handle each case.

Stuck Migration

A migration that failed partway through leaves the database in an inconsistent state:

# Check status
bin/rails db:migrate:status

# If a migration shows 'down' but its changes are partially applied:
# Fix the database manually, then mark it as run
bin/rails db:migrate:up VERSION=20240115120000

Pending Migration in Production

# Add this to config/environments/production.rb
# to prevent app boot with pending migrations
config.active_record.migration_error = :page_load

Safe Migration Patterns

For zero-downtime deploys, avoid locking operations:

class AddIndexToUsersEmail < ActiveRecord::Migration[7.0]
  disable_ddl_transaction!

  def change
    # CONCURRENTLY doesn't lock the table
    add_index :users, :email, algorithm: :concurrently
  end
end

Irreversible Migration Fix

class ChangeColumnType < ActiveRecord::Migration[7.0]
  def up
    change_column :products, :price, :decimal, precision: 10, scale: 2
  end

  def down
    change_column :products, :price, :float
  end
end

Schema Conflicts After Merge

# Regenerate schema.rb from the database
bin/rails db:schema:dump

Never manually edit schema.rb — it's auto-generated.

Bugsly captures ActiveRecord::PendingMigrationError and other migration-related exceptions, alerting your team when a deployment leaves the database in a mismatched state.