已安裝Searchlogic gem，但無法訪問方法

Question

我剛剛安裝了searchlogic gem，但是當我嘗試通過控制台訪問基本方法時，出現以下錯誤：

>> User.username_not_null
NoMethodError: undefined method `username_not_null' for #<Class:0x1033a1d90>
    from /Library/Ruby/Gems/1.8/gems/searchlogic-2.4.27/lib/searchlogic/named_scopes/conditions.rb:81:in `method_missing'
    from /Library/Ruby/Gems/1.8/gems/searchlogic-2.4.27/lib/searchlogic/named_scopes/association_conditions.rb:19:in `method_missing'
    from /Library/Ruby/Gems/1.8/gems/searchlogic-2.4.27/lib/searchlogic/named_scopes/association_ordering.rb:27:in `method_missing'
    from /Library/Ruby/Gems/1.8/gems/searchlogic-2.4.27/lib/searchlogic/named_scopes/ordering.rb:30:in `method_missing'
    from /Library/Ruby/Gems/1.8/gems/searchlogic-2.4.27/lib/searchlogic/named_scopes/or_conditions.rb:28:in `method_missing'
    from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/gems/1.8/gems/activerecord-2.3.5/lib/active_record/base.rb:1959:in `method_missing'
    from (irb):1

我仍然無法掌握Gems的常識，這常常使我陷入困境-有人能指出我正確的方向來解決此問題嗎？

Answer 1

不要將Searchlogic用於可以將Rails用於以下用途：

 User.all(:conditions => ["username IS NOT NULL"])