[Ruby-On-Rails] How to express a NOT IN query with ActiveRecord/Rails?


Answers

FYI, In Rails 4, you can use not syntax:

Article.where.not(title: ['Rails 3', 'Rails 5'])
Question

Just to update this since it seems a lot of people come to this, if you are using Rails 4 look at the answers by Trung Lê` and VinniVidiVicci.

Topic.where.not(forum_id:@forums.map(&:id))

Topic.where(published:true).where.not(forum_id:@forums.map(&:id))

I'm hoping there is a easy solution that doesn't involve find_by_sql, if not then I guess that will have to work.

I found this article which references this:

Topic.find(:all, :conditions => { :forum_id => @forums.map(&:id) })

which is the same as

SELECT * FROM topics WHERE forum_id IN (<@forum ids>)

I am wondering if there is a way to do NOT IN with that, like:

SELECT * FROM topics WHERE forum_id NOT IN (<@forum ids>)



The accepted solution fails if @forums is empty. To workaround this I had to do

Topic.find(:all, :conditions => ['forum_id not in (?)', (@forums.empty? ? '' : @forums.map(&:id))])

Or, if using Rails 3+:

Topic.where( 'forum_id not in (?)', (@forums.empty? ? '' : @forums.map(&:id)) ).all



Using Arel:

topics=Topic.arel_table
Topic.where(topics[:forum_id].not_in(@forum_ids))

or, if preferred:

topics=Topic.arel_table
Topic.where(topics[:forum_id].in(@forum_ids).not)

and since rails 4 on:

topics=Topic.arel_table
Topic.where.not(topics[:forum_id].in(@forum_ids))

Please notice that eventually you do not want the forum_ids to be the ids list, but rather a subquery, if so then you should do something like this before getting the topics:

@forum_ids = Forum.where(/*whatever conditions are desirable*/).select(:id)

in this way you get everything in a single query: something like:

select * from topic 
where forum_id in (select id 
                   from forum 
                   where /*whatever conditions are desirable*/)

Also notice that eventually you do not want to do this, but rather a join - what might be more efficient.




You may want to have a look at the meta_where plugin by Ernie Miller. Your SQL statement:

SELECT * FROM topics WHERE forum_id NOT IN (<@forum ids>)

...could be expressed like this:

Topic.where(:forum_id.nin => @forum_ids)

Ryan Bates of Railscasts created a nice screencast explaining MetaWhere.

Not sure if this is what you're looking for but to my eyes it certainly looks better than an embedded SQL query.




This way optimizes for readability, but it's not as efficient in terms of database queries:

# Retrieve all topics, then use array subtraction to
# find the ones not in our list
Topic.all - @forums.map(&:id)



You can use sql in your conditions:

Topic.find(:all, :conditions => [ "forum_id NOT IN (?)", @forums.map(&:id)])



When you query a blank array add "<< 0" to the array in the where block so it doesn't return "NULL" and break the query.

Topic.where('id not in (?)',actions << 0)

If actions could be an empty or blank array.




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