execute joins manually without :include parameter

Hi!

I have the next model with the follow associations:

class XmlGen < ActiveRecord::Base   set_primary_key "pk"   belongs_to :serie,              :foreign_key => "series_fk"

class Serie < ActiveRecord::Base   set_primary_key "pk"   belongs_to :study, #Relaciones entre las clases Study y Series. A study has many series.              :foreign_key => "study_fk"   has_many :xml_genes

I did the follow query:

@instances = Instance.find(:all, :include => [:serie, {:serie=>:study}])

but the query is so slow. I want to try do the query manually, with the option :joins. How do I do this query, exactly, the parameter :joins?

Thanks in advance!