Add emoji support for mysql

config_database.yml

default: &default
  adapter: mysql2
  encoding: utf8mb4
  charset: utf8mb4
  collation: utf8mb4_unicode_ci

config_initializers_mysql_utf8mb4_fix.rb

require 'active_record/connection_adapters/abstract_mysql_adapter'

module ActiveRecord
  module ConnectionAdapters
    class AbstractMysqlAdapter
      NATIVE_DATABASE_TYPES[:string] = { name: 'varchar', limit: 191 }
    end
  end
end

db_migrate_add_emoji_support.rb

class AddEmojiSupport < ActiveRecord::Migration
  def up
    conn = ActiveRecord::Base.connection

    execute "ALTER DATABASE `#{conn.current_database}` CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci;"

    conn.tables.each do |table|
      conn.columns(table).each do |column|
        case column.type
        when :string, :text
          change_column table, column.name, column.type
        end
      end

      execute "ALTER TABLE `#{table}` CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;"
    end
  end

  def down
  end
end