CODEWITHSUNDEEP
ruby-on-rails
Noam B.
Noam B.

Reputation: 3250

Rails - use join only if a condition is true

How do I use joins only if a certain condition is true? For example, I have this query:

@courses = Course.find(:all,
    :order=> 'courses.name asc',
    :include => [:units],
    :joins => :course_sub_responsibles,
    :group => 'courses.name',
    :conditions => conditions)

But I need to join the course_sub_responsibles table only in a certain condition.

Upvotes: 0

Views: 2254

Answers (2)

Chen Fisher
Chen Fisher

Reputation: 1455

The ActiveRecord.find method takes a Hash as last argument (which is written without curly braces, but it is a hash indeed), which means you can do that:

options = { :order=> 'courses.name asc',
:include => [:units],
:group => 'courses.name',
:conditions => conditions }

options[:join] = :course_sub_responsibles if YOUR CONDITION GOES HERE

@courses = Course.find(:all, options)

Upvotes: 0

rewritten
rewritten

Reputation: 16435

You should use ARel-powered methods:

@courses = Course.scoped  # Course.all in rails 4
@courses = @courses.order("courses.name asc").includes(:units)
@courses = @courses.joins(:course_sub_responsibles) if YOUR_CONDITION
@courses = @courses.group("courses.name")
@courses = @courses.where(conditions)
@courses

This will only execute the query when the variable is iterated, but the query will be built by pieces, so you can add/remove pieces when you need to.

In Rails4 it will be even cleaner (note the bangs, which mean "modify the receiver" as usual):

@courses = Course.all
@courses.order!("courses.name asc")
@courses.includes!(:units)
@courses.joins!(:course_sub_responsibles) if YOUR_CONDITION
@courses.group!("courses.name")
@courses.where!(conditions)
@courses

Upvotes: 2

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