rails dynamic where sql query

Question

I have an object with a bunch of attributes that represent searchable model attributes, and I would like to dynamically create an sql query using only the attributes that are se

Answer 1

Your approach is a little off as you're trying to solve the wrong problem. You're trying to build a string to hand to ActiveRecord so that it can build a query when you should simply be trying to build a query.

When you say something like:

Model.where('a and b')

that's the same as saying:

Model.where('a').where('b')

and you can say:

Model.where('c like ?', pattern)

instead of:

Model.where("c like '#{pattern}'")

Combining those two ideas with your self.instance_values you could get something like:

def query
  self.instance_values.select { |_, v| v.present? }.inject(YourModel) do |q, (name, value)|
    q.where("#{name} like ?", "%#{value}%")
  end
end

or even:

def query
  empties      = ->(_, v) { v.blank? }
  add_to_query = ->(q, (n, v)) { q.where("#{n} like ?", "%#{v}%") }
  instance_values.reject(&empties)
                 .inject(YourModel, &add_to_query)
end

Those assume that you've properly whitelisted all your instance variables. If you haven't then you should.