What is the best way to find records with duplicate values in a column using ruby and the new Activerecord?
In Rails 2.x, select is a private method of AR class. Just use find():
klass.find(:all,
:select => "id, count(the_col) as num",
:conditions => ["extra conditions here"],
:group => 'the_col',
:having => "num > 1")
I was beating my head against this problem with a 2016 stack (Rails 4.2, Ruby 2.2), and got what I wanted with this:
> Model.select([:thing]).group(:thing).having("count(thing) > 1").all.size
=> {"name1"=>5, "name2"=>4, "name3"=>3, "name4"=>2, "name5"=>2}
Here's how I solved it with the AREL helpers, and no custom SQL:
Person.select("COUNT(last_name) as total, last_name")
.group(:last_name)
.having("COUNT(last_name) > 1")
.order(:last_name)
.map{|p| {p.last_name => p.total} }
Really, it's just a nicer way to write the SQL. This finds all records that have duplicate last_name values, and tells you how many and what the last names are in a nice hash.
Translating @TuteC into ActiveRecord:
sql = 'SELECT id,
COUNT(id) as quantity
FROM types
GROUP BY name
HAVING quantity > 1'
#=>
Type.select("id, count(id) as quantity")
.group(:name)
.having("quantity > 1")
With custom SQL, this finds types
with same values for name
:
sql = 'SELECT id, COUNT(id) as quantity FROM types
GROUP BY name HAVING quantity > 1'
repeated = ActiveRecord::Base.connection.execute(sql)
Here is a solution that extends the other answers to show how to find and iterate through the records grouped by the duplicate field:
duplicate_values = Model.group(:field).having(Model.arel_table[:field].count.gt(1)).count.keys
Model.where(field: duplicate_values).group_by(&:field).each do |value, records|
puts "The records with ids #{records.map(&:id).to_sentence} have field set to #{value}"
end
It seems a shame this has to be done with two queries but this answer confirms this approach.