Extract iterator method in AR::SchemaDumper

[calebhearth]

Gems which wish to tie into ActiveRecord::SchemaDumper need to duplicate this
logic currently. Foreigner is one such example, as is a library I'm
currently working on but which hasn't been released yet:

def tables_with_foreign_keys(stream)
  tables_without_foreign_keys(stream)
  @connection.tables.sort.each do |table|
    next if ['schema_migrations', ignore_tables].flatten.any? do |ignored|
      case ignored
      when String; table == ignored
      when Regexp; table =~ ignored
      else
        raise StandardError, 'ActiveRecord::SchemaDumper.ignore_tables accepts an array of String and / or Regexp values.'
      end
    end
    foreign_keys(table, stream)
  end
end

Extract the skip logic to a method, making it much simpler to follow this same
behavior in gems that are tying into the migration flow and let them dump only
tables that aren't skipped without copying this block of code. The above code
could then be simplified to:

    def tables_with_foreign_keys(stream)
      tables_without_foreign_keys(stream)
      @connection.tables.sort.each do |table|
        foreign_keys(table, stream) unless ignored?(table)
      end
    end

This could be further simplified to assume tables, but for my use case I'm
trying to add views which wouldn't be returned by the tables method.

[calebhearth]

@schneems @derekprior

[calebhearth]

Since I now realize it may not be clear, the functionality I'm moving around is what lets ActiveRecord::SchemaDumper.ignore_tables skip specific tables when dumping to db/schema.rb.

https://github.com/calebthompson/rails/blob/extract-iterator-method/activerecord/lib/active_record/schema_dumper.rb#L14-L16

[schneems]

👍 the change is relatively trivial, and the resulting method extraction is cleaner. If it provides a useful interface in the process i'm for it.