Add foreign_key option for belongs_to association
Belongs_to association with custom primary_key
Rename to #get_record
Belongs_to primary_key for AR only
Raise an error if custom primary key for non-AR

Could do it when the association is defined, but
that would not handle polymorphic associations
Use find_by rather than where for belongs_to query
Merge pull request #1 from data-axle/belongs_to_options

Belongs_to  association takes additional options