Is is possible in Rails > 3.2 to add conditions to the join statement generated by the includes
method?
Let's say I have two models, Person and Note. Each person has many notes and each note belong to one person. Each note has an attribute important
.
I want to find all the people preloading only the notes that are important. In SQL that will be:
SELECT * FROM people LEFT JOIN notes ON notes.person_id = people.id AND notes.important = 't'
In Rails, the only similar way to do that is using includes
(note: joins
won't preload notes) like this:
Person.includes(:notes).where(:important, true)
However, that will generate the following SQL query which returns a different result set:
SELECT * FROM people LEFT JOIN notes ON notes.person_id = people.id WHERE notes.important = 't'
Please, notice that the first resultset includes all the people and the second one only the people associated to important notes.
Also notice that :conditions are deprecated since 3.1.
According to this guide Active Record Querying
You can specify conditions on includes for eager loading like this
Person.includes(:notes).where("notes.important", true)
It recommends to use joins
anyway.
A workaround for this would be to create another association like this
class Person < ActiveRecord::Base has_many :important_notes, :class_name => 'Note', :conditions => ['important = ?', true] end
You would then be able to do this
Person.find(:all, include: :important_notes)
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