Problem installing gems

I had recently used datamapper, and then all of a sudden it didn't work. I keep getting this error:

/Users/paul/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require': no such file to load -- dm-mysql-adapter (LoadError)
    from /Users/paul/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
    from /Users/paul/.rvm/gems/ruby-1.9.2-p180/gems/dm-core-1.1.0/lib/dm-core/adapters.rb:163:in `load_adapter'
    from /Users/paul/.rvm/gems/ruby-1.9.2-p180/gems/dm-core-1.1.0/lib/dm-core/adapters.rb:133:in `adapter_class'
    from /Users/paul/.rvm/gems/ruby-1.9.2-p180/gems/dm-core-1.1.0/lib/dm-core/adapters.rb:13:in `new'
    from /Users/paul/.rvm/gems/ruby-1.9.2-p180/gems/dm-core-1.1.0/lib/dm-core.rb开发者_如何学Python:219:in `setup'

Then, when I try to load the dm-mysql-adapter, it gives me this error:

/Users/paul/.rvm/rubies/ruby-1.9.2-p180/bin/ruby extconf.rb --with-mysql-config=/usr/bin/mysql_config
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers.  Check the mkmf.log file for more
details.  You may need configuration options.

I've seen similar error messages when I'm googling, but none of the responses seem to work for me...