将参数传递给SQL查询

Question

So, in my rails app I developed a search filter where I am using sliders. For example, I want to show orders where the price is between min value and max value which comes from the slider in params. I have column in my db called "price" and params[:priceMin], params[:priceMax]. So I can't write something kinda MyModel.where(params)... . You may say, that I should do something like MyModel.where('price >= ? AND price <= ?', params[:priceMin], params[:priceMax]) but there is a problem: the number of search criteria depends on user desire, so I don't know the size of params hash that passes to query. Are there any ways to solve this problem?

UPDATE

I've already done it this way

def query_senders
query = ""
if params.has_key?(:place_from)
  query += query_and(query) + "place_from='#{params[:place_from]}'"
end
if params.has_key?(:expected_price_min) and params.has_key?(:expected_price_max)
      query += query_and(query) + "price >= '#{params[:expected_price_min]}' AND price <= '#{params[:expected_price_max]}'"
end...

but according to ruby guides ( http://guides.rubyonrails.org/active_record_querying.html ) this approach is bad because of SQL injection danger.

Answer 1

You can get the size of params hash by doing params.count . By the way you described it, it still seems that you will know what parameters can be passed by the user. So just check whether they're present, and split the query accordingly.

Edited:

def query_string
  return = {}
  if params[:whatever].present?
     return.merge({whatever: #{params[:whatever]}}"
  elsif ...
end

The above would form a hash for all of the exact values you're searching for, avoiding SQL injection. Then for such filters as prices you can just check whether the values are in correct format (numbers only) and only perform if so.