Rails - Iterating through nested arrays

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October 11th, 2010, 04:31 PM

oprogfrogo

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Rails - Iterating through nested arrays

Hi I'm very new to rails and need some help on iterating through nested arrays. I'm trying to figure out how to do mass-inserts for each values that is different between the make, model and color of cars.

The params that are pass are:

"make" => ["Honda", "Honda"],
"model" => ["Civic", "Accord"],
"color" => [{"Black", "White", "Red"}, {"Black", "White"}]

So with these params passed, I wanted to have 5 inserts to occur.

1. Civic - Black
2. Civic - White
3. Civic - Red
4. Accord - Black
5. Accord - White

Here what I've got so far that pushes the insert query that builds it. But I'm unsure how to make it insert 5 times according to what I've listed above:

Code:

def self.cars(make, model, color)
  inserts = []
    color.each do |i|
      inserts.push "('#{make}', '#{model}', '#{i}')"
     end

  Foo.connection.execute "INSERT INTO car_inventory (make, model, color) VALUES #{inserts.join(", ")}"
end

Please help.

October 11th, 2010, 05:08 PM

L7Sqr

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Arrays have a method called each_with_index which is what it looks like you want. Consider the following:

Code:

irb(main):001:0> make = ["honda", "honda"]
=> ["honda", "honda"]
irb(main):002:0> model = ["civic", "accord"]
=> ["civic", "accord"]
irb(main):003:0> color = [["black", "white", "red"], ["black", "white"]]
=> [["black", "white", "red"], ["black", "white"]]
irb(main):004:0> make.uniq.each do |mk|
irb(main):005:1*    model.each_with_index do |mdl, idx|
irb(main):006:2*       color[idx].each do |col|
irb(main):007:3*          puts "#{mk}:#{mdl}:#{col}"
irb(main):008:3>       end
irb(main):009:2>    end
irb(main):010:1> end
honda:civic:black
honda:civic:white
honda:civic:red
honda:accord:black
honda:accord:white

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October 11th, 2010, 10:18 PM

oprogfrogo

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L7Sqr, Thanks for the reply, which helps me understand this better. But let's say my form (using form_for) has 3 checkboxes for Black, White, and Red. With all the colors checked, the values are loaded into mass-assignment called 'car' as shown below:

Code:

"car"=>{"make"=>"Honda", "color"=>["0", "Black", "0", "White", "0", "Red"], "model"=>"Accord", "tinted"=>"yes"}}

(Not sure why the check_box helper puts '0' along with the values but I'm sure I can place a conditional to work around that.)

So with that mass-assignment, is it possible to put some code in the model that iterates through each color and does 3 inserts?

October 12th, 2010, 05:01 AM

L7Sqr

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Code:

irb(main):001:0> hash = {}
=> {}
irb(main):002:0> hash["car"] = {"make"=>"Honda", "color"=>["0", "Black", "0", "White", "0", "Red"], "model"=>"Accord", "tinted"=>"yes"}
=> {"model"=>"Accord", "tinted"=>"yes", "color"=>["0", "Black", "0", "White", "0", "Red"], "make"=>"Honda"}
irb(main):003:0> car = hash["car"]
=> {"model"=>"Accord", "tinted"=>"yes", "color"=>["0", "Black", "0", "White", "0", "Red"], "make"=>"Honda"}
irb(main):004:0> make = car["make"]
=> "Honda"
irb(main):005:0> model = car["model"]
=> "Accord"
irb(main):006:0> colors = car["color"]
=> ["0", "Black", "0", "White", "0", "Red"]
irb(main):007:0> [1,3,5].each do |i|
irb(main):008:1*    puts "(#{make}, #{model}, #{colors[i]})"
irb(main):009:1> end
(Honda, Accord, Black)
(Honda, Accord, White)
(Honda, Accord, Red)
=> [1, 3, 5]
irb(main):010:0>

What you'd like to do is convert the color array into a hash but the order of the elements prevents that directly due to multiple assignments to the same key. For instance

Code:

irb(main):001:0> colors = ["0", "Black", "0", "White", "0", "Red"]
=> ["0", "Black", "0", "White", "0", "Red"]
irb(main):002:0> Hash[*colors]
=> {"0"=>"Red"}
irb(main):003:0> colors = ["Black", "0", "White", "0", "Red", "0"]
=> ["Black", "0", "White", "0", "Red", "0"]
irb(main):004:0> Hash[*colors]
=> {"Black"=>"0", "Red"=>"0", "White"=>"0"}
irb(main):005:0>

Which is why I used the array of 1, 3, 5 to index the color values. This is brittle and as you add colors this will break. The best way to do that is to convert the color array to an appropriate structure and iterate through that directly.

October 12th, 2010, 03:07 PM

oprogfrogo

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Quote:

Originally Posted by L7Sqr

Code:

irb(main):001:0> hash = {}
=> {}
irb(main):002:0> hash["car"] = {"make"=>"Honda", "color"=>["0", "Black", "0", "White", "0", "Red"], "model"=>"Accord", "tinted"=>"yes"}
=> {"model"=>"Accord", "tinted"=>"yes", "color"=>["0", "Black", "0", "White", "0", "Red"], "make"=>"Honda"}
irb(main):003:0> car = hash["car"]
=> {"model"=>"Accord", "tinted"=>"yes", "color"=>["0", "Black", "0", "White", "0", "Red"], "make"=>"Honda"}
irb(main):004:0> make = car["make"]
=> "Honda"
irb(main):005:0> model = car["model"]
=> "Accord"
irb(main):006:0> colors = car["color"]
=> ["0", "Black", "0", "White", "0", "Red"]
irb(main):007:0> [1,3,5].each do |i|
irb(main):008:1*    puts "(#{make}, #{model}, #{colors[i]})"
irb(main):009:1> end
(Honda, Accord, Black)
(Honda, Accord, White)
(Honda, Accord, Red)
=> [1, 3, 5]
irb(main):010:0>

What you'd like to do is convert the color array into a hash but the order of the elements prevents that directly due to multiple assignments to the same key. For instance

Code:

irb(main):001:0> colors = ["0", "Black", "0", "White", "0", "Red"]
=> ["0", "Black", "0", "White", "0", "Red"]
irb(main):002:0> Hash[*colors]
=> {"0"=>"Red"}
irb(main):003:0> colors = ["Black", "0", "White", "0", "Red", "0"]
=> ["Black", "0", "White", "0", "Red", "0"]
irb(main):004:0> Hash[*colors]
=> {"Black"=>"0", "Red"=>"0", "White"=>"0"}
irb(main):005:0>

Would you know the Rails way of making this work so that the values are inserted into the db 3 times at once?

October 12th, 2010, 05:44 PM

L7Sqr

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I would not. Rails is a framework built on top of Ruby and I've neither needed nor bothered to learn it. However, under the interface, you are going to be iterating over an enumeration of values and joining them somehow to make your SQL statements.

There are people here who have used rails more than myself and maybe they will assist - if not you can start to look at how things are done by digging through the code.

Rails - Iterating through nested arrays

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