Question

The code below is from a Sinatra app (that uses DataMappe), which I am trying to convert to a Rails 3 application. It is a class method in the Visit class.

def self.count_by_date_with(identifier,num_of_days)
    visits = repository(:default).adapter.query("SELECT date(created_at) as date, count(*) as count FROM visits where link_identifier = '#{identifier}' and created_at between CURRENT_DATE-#{num_of_days} and CURRENT_DATE+1 group by date(created_at)")
    dates = (Date.today-num_of_days..Date.today)
    results = {}
    dates.each { |date|
      visits.each { |visit| results[date] = visit.count if visit.date == date }
      results[date] = 0 unless results[date]
    }
    results.sort.reverse    
  end

My problem is with this part

 visits = repository(:default).adapter.query("SELECT date(created_at) as date, count(*) as count FROM visits where link_identifier = '#{identifier}' and created_at between CURRENT_DATE-#{num_of_days} and CURRENT_DATE+1 group by date(created_at)")

Rails (as far as I know) doesn’t have this repository method, and I would expect a query to be called on an object of some sort, such as Visit.find

Can anyone give me a hint how this would best be written for a Rails app?

Should I do

Visit.find_by_sql("SELECT date(created_at) as date, count(*) as count FROM visits where link_identifier = '#{identifier}' and created_at between CURRENT_DATE-#{num_of_days} and CURRENT_DATE+1 group by date(created_at)")

Answer 1

I know you already accepted an answer, but you asked for the best way to do what you asked in Rails. I’m providing this answer because Rails does not recommend building conditions as pure query strings.

Building your own conditions as pure strings can leave you vulnerable to SQL injection exploits. For example, Client.where("first_name LIKE '%#{params[:first_name]}%'") is not safe.

Fortunately, Active Record is incredibly powerful and can build very complex queries. For instance, your query can be recreated with four method calls while still being easy to read and safe.

# will return a hash with the structure
# {"__DATE__" => __COUNT__, ...}
def self.count_by_date_with(identifier, num_of_days)
  where("link_identifier = ?", identifier)
  .where(:created_at => (num_of_days.to_i.days.ago)..(1.day.from_now))
  .group('date(created_at)')
  .count
end

Active Record has been built to turn Ruby objects into valid SQL selectors and operators. What makes this so cool is that Rails can turn a Ruby Range into a BETWEEN operator or an Array into an IN expression.

For more information on Active Record check out the guide. It explains what Active Record is capable of and how to use it.