Question

In one particular Railcasts episode Ryan talks about advanced search and in that he uses some code so as to find the conditions for the search. As its working isn’t explained I wanted some clarification regarding it.

def products
 @products ||= find_products
end

private

def find_products
 Product.find(:all, :conditions => conditions)
end

def keyword_conditions
["products.name LIKE ?", "%#{keywords}%"] unless keywords.blank?
end

def minimum_price_conditions
 ["products.price >= ?", minimum_price] unless minimum_price.blank?
end

def maximum_price_conditions
 ["products.price <= ?", maximum_price] unless maximum_price.blank?
end

def category_conditions
 ["products.category_id = ?", category_id] unless category_id.blank?
end

def conditions
 [conditions_clauses.join(' AND '), *conditions_options]
end

def conditions_clauses
 conditions_parts.map { |condition| condition.first }
end

def conditions_options
 conditions_parts.map { |condition| condition[1..-1] }.flatten
end

def conditions_parts
 private_methods(false).grep(/_conditions$/).map { |m| send(m) }.compact
end

I would welcome any information as to how this works especially the method products as he even calls it as products.name etc.

Answer 1

He defines some methods for the conditions in his search form: keyword_conditions, minimum_price_conditions ans so on. products.name means the field name from the table products.

The method

def conditions_parts
  private_methods(false).grep(/_conditions$/).map { |m| send(m) }.compact
end

uses reflection to look at the private methods of this class which have the name that ends with _conditions (The regex /_conditions$/) and joins only those that don’t return null (compact)

The method

def conditions
  [conditions_clauses.join(' AND '), *conditions_options]
end

adds a AND keyword between the conditions and passes the result to Product.find which makes the SQL query and returns the result set.