mysql2 gem, Rails 3.0.3 and "incompatible character encodings" errors

I'm using Rails 3.0.3, and I have changed the mysql adapter from ruby-mysql to mysql2, but now I have the following error:

incompatible character encodings: ASCII-8BIT and UTF-8

I have read everywhere about this, but I cant manage to fix it.

application.rb:

config.encoding = "utf-8"

database.yml:

development:   
  adapter: mysql2
  encoding: utf8
  database: rails3_development
  username: root
  password:
  host: localhost

Gems:

specs:
  abstract (1.0.0)
  actionmailer (3.0.3)
  actionpack (3.0.3)
  activemodel (3.0.3)
  activerecord (3.0.3)
  activeresource (3.0.3)
  activesupport (3.0.3)
  arel (2.0.7)
  bcrypt-ruby (2.1.4)
  builder (2.1.2)
  erubis (2.6.6)
  i18n (0.5.0)
  jquery-开发者_运维问答rails (0.2.6)
  mail (2.2.15)
  mime-types (1.16)
  **mysql2 (0.2.6)
  orm_adapter (0.0.4)
  paperclip (2.3.8)
  polyglot (0.3.1)
  rack (1.2.1)
  rack-mount (0.6.13)
  rack-test (0.5.7)
  rails (3.0.3)
  railties (3.0.3)
  rake (0.8.7)
  thor (0.14.6)
  treetop (1.4.9)
  tzinfo (0.3.24)
  warden (1.0.3)
  will_paginate (3.0.pre2)

I have a similar problem: a varchar field with collation utf8_bin having an ASCII-8BIT encoding.

The problem lies in the mysql2 gem, not in Rails, nor in the mysql settings, in my case at least, because it doesn't occur with the ruby-mysql gem.

Please test if the problem goes away when you switch to ruby-mysql.

The following code, run from irb on ruby 1.9.2, demonstrates the problem:

require 'mysql2'
c = Mysql2::Client.new(host: "localhost", username: "root", database: 'd')
c.query("select word from t where word = 'a'").to_a[0]["word"].encoding
# => #<Encoding:ASCII-8BIT>

This on a mysql database where every conceivable setting has been set to a utf8_bin collation.

In the mysql2 gem, in the result.c file on line 253, there's the following snippet:

if (fields[i].flags & BINARY_FLAG) {
  rb_enc_associate(val, binaryEncoding);
} else ...

I believe this is where the binary (ASCII-8BIT) encoding is being set, maybe because of the utf8_bin collation... I've removed it, and it solved the problem, but I'm sure it will probably introduce other problems, with blobs for instance.