Raise an exception when model without primary key calls .find_with_ids

[makimoto]

I fixed exception handling for .find of models without primary key.

Now .find by models without primary key raises StatementInvalid exception by the invalid SQL query, but I think an exception should be raised before building a query.

irb(main):001:0> Post.find(1)
  Post Load (0.3ms)  SELECT  `posts`.* FROM `posts`  WHERE `posts`.`` = 1 LIMIT 1
Mysql2::Error: Unknown column 'posts.' in 'where clause': SELECT  `posts`.* FROM `posts`  WHERE `posts`.`` = 1 LIMIT 1
ActiveRecord::StatementInvalid: Mysql2::Error: Unknown column 'posts.' in 'where clause': SELECT  `posts`.* FROM `posts`  WHERE `posts`.`` = 1 LIMIT 1
    from /Users/makimoto/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/bundler/gems/rails-dd37ff81d131/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:293:in `query'

By this PR AR::UnknownPrimaryKey are raised when Model.primary_key is nil and Model.find calls.

irb(main):001:0> Post.find(1)
ActiveRecord::UnknownPrimaryKey: Unknown primary key for table posts in model Post.
    from /Users/makimoto/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/bundler/gems/rails-dd37ff81d131/activerecord/lib/active_record/relation/finder_methods.rb:301:in `find_with_ids'

[pftg]

what do yu think about using: assert_raises instead of rescue?

[pftg]

To complete PR needs to add Changelog entry.

[makimoto]

@pftg done. thanks!

[senny]

Can you use one of the existing models, that does in fact not have a primary key? Maybe Matey?

EDIT: This way we don't need to mess with global state.

[makimoto]

Oh, I didn't know Matey.
I use it. 17c08fd

[senny]

@makimoto the PR does not apply, can you push a rebased version?

[makimoto]

ok, rebased and pushed.

[senny]

@makimoto thank you for your contribution 💛