A ruby script to help automate getting a Rails application out of MySQL's character encoding hell.

latin1-to-utf8.rb

# The below script attempts to automate the character encoding challenges
# encountered with mysql, latin1 and UTF8
# http://www.bluebox.net/news/2009/07/mysql_encoding/

# ==============================================================================
# Copyright © 2013 University of Notre Dame
# Additional copyright may be held by others, as reflected in the commit history.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================

DB_CONFIG = YAML.load_file(Rails.root.join('config/database.yml').to_s)[Rails.env]

DB_CONFIG['username'] ||= 'root'

MYSQL_PARAMS = "-u#{DB_CONFIG['username']} #{'-p' << DB_CONFIG['password'] if DB_CONFIG['password']} #{'-h' << DB_CONFIG['host'] if DB_CONFIG['host']} #{DB_CONFIG['database']}".freeze

def load_new_database
  sql_filename = Rails.root.join('db/db.sql')
  system("mysql #{MYSQL_PARAMS} < #{sql_filename}")
end

def attempt_conversion
  ActiveRecord::Base.connection.select_all(%(show table status where collation like '%latin1%')).each do |options|
    table_name = options['Name']
    puts "Started Processing\t#{table_name}"
    FileUtils.mkdir_p(Rails.root.join('tmp/db-conversion'))
    filename_pre_transform = Rails.root.join("tmp/db-conversion/conductor.#{table_name}.pre.sql").to_s
    commands = []
    commands << %(mysqldump #{MYSQL_PARAMS} --opt --skip-set-charset --default-character-set=latin1 --skip-extended-insert --tables #{table_name} > #{filename_pre_transform})
    commands << %(perl -i -pe 's/DEFAULT CHARSET=latin1/DEFAULT CHARSET=utf8/' #{filename_pre_transform})
    filename_to_load = filename_pre_transform
    commands << %(mysql #{MYSQL_PARAMS} < #{filename_to_load})
    system(commands.join(';'))
    puts "Finished Processing\t#{table_name}"
  end
end

def verify_character_encoding_at_table_level
  schema_query = %(
  SELECT TABLE_SCHEMA,
  TABLE_NAME,
  CCSA.CHARACTER_SET_NAME AS DEFAULT_CHAR_SET,
  COLUMN_NAME,
  COLUMN_TYPE,
  C.CHARACTER_SET_NAME
  FROM information_schema.TABLES AS T
  JOIN information_schema.COLUMNS AS C USING (TABLE_SCHEMA, TABLE_NAME)
  JOIN information_schema.COLLATION_CHARACTER_SET_APPLICABILITY AS CCSA
  ON (T.TABLE_COLLATION = CCSA.COLLATION_NAME)
  WHERE TABLE_SCHEMA=SCHEMA()
  AND C.DATA_TYPE IN ('enum', 'varchar', 'char', 'text', 'mediumtext', 'longtext')
  ORDER BY TABLE_SCHEMA,
  TABLE_NAME,
  COLUMN_NAME
  )
  ActiveRecord::Base.connection.select_all(schema_query).each do |options|
    table_name = options['TABLE_NAME']
    column_name = options['COLUMN_NAME']
    sub_query = "SELECT count(`#{column_name}`) AS count FROM `#{table_name}` WHERE LENGTH(`#{column_name}`) != CHAR_LENGTH(`#{column_name}`);"
    response = ActiveRecord::Base.connection.select_one(sub_query)
    if response['count'].to_i > 0
      puts "Found `#{table_name}`.`#{column_name}`\t#{response['count']}"
      convert_double_encoded(table_name, column_name, options['COLUMN_TYPE'])
    end
  end
end

def convert_double_encoded(table_name, column_name, column_type)
  puts "Processing `#{table_name}`.`#{column_name}`"
  # normalized_column_type = column_type.sub(/\([^\)]\)/,'').strip
  temp_table_name = "temp_#{table_name}_#{column_name}"
  ActiveRecord::Base.connection.execute(
    "DROP TABLE IF EXISTS `#{temp_table_name}`"
  )
    
  ActiveRecord::Base.connection.execute(
    "CREATE TABLE `#{temp_table_name}`
      (
        SELECT * FROM `#{table_name}`
        WHERE LENGTH(`#{column_name}`) != CHAR_LENGTH(`#{column_name}`)
      )"
  )
  
  ActiveRecord::Base.connection.execute(
    "ALTER TABLE `#{temp_table_name}` 
      MODIFY `#{temp_table_name}`.`#{column_name}` #{column_type} CHARACTER SET latin1"
  )

  ActiveRecord::Base.connection.execute(
    "ALTER TABLE `#{temp_table_name}` 
      MODIFY `#{temp_table_name}`.`#{column_name}` BLOB"
  )

  ActiveRecord::Base.connection.execute(
    "ALTER TABLE `#{temp_table_name}` 
      MODIFY `#{temp_table_name}`.`#{column_name}` #{column_type} CHARACTER SET UTF8"
  )

  ActiveRecord::Base.connection.execute(
    "DELETE FROM `#{temp_table_name}`
      WHERE LENGTH(`#{column_name}`) = CHAR_LENGTH(`#{column_name}`)"
  )

  ActiveRecord::Base.connection.execute(
    "REPLACE INTO `#{table_name}` (SELECT * FROM `#{temp_table_name}`)"
  )

  ActiveRecord::Base.connection.execute(
    "DROP TABLE IF EXISTS `#{temp_table_name}`"
  )

end

# load_new_database
attempt_conversion
verify_character_encoding_at_table_level