Rails 4 introduced raising an error on pending migrations Show archive.org snapshot . This is most annoying when you are crafting a migration but need to play with your application to figure out how to do it.

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To disable this behavior, just set the corresponding config option to false:

# in config/environments/development.rb

# Raise an error on page load if there are pending migrations.
config.active_record.migration_error = false # was :page_load