Restore a rails DB from ibd files in a backup folder but missing schema definition...

Restore from innodb datafiles instructions.txt

# Backstory - I had accidentally deleted /usr/local/mysql/data/mysql.ibd and 
#            as a result lost all schema information for all dbs...
#

# 1) move the db data folder someplace safe:
mv /usr/local/mysql/data/my_rails_db /backups/my_rails_db

# 2) recreate the db with the rails app and create the same (empty) schema
rake db:create
rake db:migrate

# 3) generate a drop_tablespaces.sql file
echo "SET FOREIGN_KEY_CHECKS=0;" > drop_tablespaces.sql
sudo ls /backups/my_rails_db/ | grep ibd | sed 's/\(.*\).ibd/alter table \1 discard tablespace; show warnings;/g' >> drop_tablespaces.sql

# 4) generate an import_tablespaces.sql file
sudo ls /backups/my_rails_db/ | grep ibd | sed 's/\(.*\).ibd/alter table \1 import tablespace; show warnings;/g' >> import_tablespaces.sql

# 5) login to mysql
mysql -uroot -p

# 6) run all commands in drop_tablespaces.sql file...
#   (in mysql client)
SET FOREIGN_KEY_CHECKS=0;
alter table app_settings discard tablespace; show warnings;
alter table ar_internal_metadata discard tablespace; show warnings;
...

# 7) copy backed up tablespaces back into mysql data
#    (from command line)
sudo cp -R /backups/my_rails_db/* /usr/local/mysql/data/my_rails_db

# 8) re-chown the copied files
#    (from command line)
sudo chown -R _mysql:_mysql /usr/local/mysql/data/my_rails_db

# 9) run all commands in import_tablespaces.sql file...
#    (in mysql client)
alter table app_settings import tablespace; show warnings;
alter table ar_internal_metadata import tablespace; show warnings;
...

# cheers :)