Right now I'm doing something like this to select a single column of data:
points = Post.find_by_sql("select point from posts")
Then passing them to a method, I'd like my method to remain agnostic, and now have to call hash.point from within my method. How can I quickly convert this into an array and pass the data set to my method, or is there a better way?
In Rails 3.2 there is a pluck method for this
Just like this:
Person.pluck(:id) # SELECT people.id FROM people
Person.pluck(:role).uniq # unique roles from array of people
Person.distinct.pluck(:role) # SELECT DISTINCT role FROM people SQL
Person.where(:confirmed => true).limit(5).pluck(:id)
Person.ids.
distinct instead of uniq: so Person.distinct.pluck(:role)You should use the pluck method as @alony suggested. If you are stuck before Rails 3.2 you can use the ActiveRecord select method together with Array#map:
Post.select(:point).map(&:point)
#=> ["foo", "bar", "baz"]
before Ruby 1.9 you'd have to do .map{|x| x.title} though, because Symbol#to_proc (aliased by the unary & operator) is not defined in earlier versions of Ruby.
If you see the definition of select_values , then it using 'map(&:field_name)'
def select_values(arel, name = nil)
result = select_rows(to_sql(arel), name)
result.map { |v| v[0] }
end
The common and general Rails way to collect all the fields values in array is like :
points = Post.all(:select => 'point').map(&:point)
Post.select(:point).limit(1) performs SELECT point FROM "posts" LIMIT 1 whereas Post.all(:select => :point).limit(1) raises a NoMethodError. Please correct me if i'm wrong.
points = Post.all.collect {|p| p.point}
select statement only fetches the specified columns.