Unpacking an array of records/fields in ruby - ruby-on-rails

Question

Having trouble unpacking an array that is generated by rails. The array looks okay and makes sense, but unpacking it doesn't.
Here is the ruby code I have written to test it:
assets = {"0"=>{"id"=>"1", "add_asset"=>"0"},
"1"=>{"id"=>"2", "add_asset"=>"0"},
"2"=>{"id"=>"3", "add_asset"=>"1"}}
puts "assets= " + assets.to_s
puts "size = " + assets.length.to_s
assets.each_with_index do |check, i|
puts "--i = " + i.to_s
this = check[i]
puts "this = " + this.to_s
puts "id = " + this["id"].to_s
puts "add = " + this["add_asset"].to_s
end
And here is the result I am getting:
d:\Users\Michael\Documents>ruby test.rb
assets= {"0"=>{"id"=>"1", "add_asset"=>"0"}, "1"=>{"id"=>"2", "add_asset"=>"0"}, "2"=>{"id"=>"3", "add_asset"=>"1"}}
size = 3
--i = 0
this = 0
id =
add =
--i = 1
this = {"id"=>"2", "add_asset"=>"0"}
id = 2
add = 0
--i = 2
this =
test.rb:14:in `block in <main>': undefined method `[]' for nil:NilClass (NoMethodError)
from test.rb:10:in `each'
from test.rb:10:in `each_with_index'
from test.rb:10:in `<main>'
Questions:
Why is it failing to read record "0" then successfully reading record "1"?
Why is it bombing completely on record "2"?

Answer 1

Don't use each_with_index. You're iterating over a hash, not an array. To iterate over the keys and values of a hash, use hash.each |key,value|.
each_with_index converts your hash to an array, in the form [ [key1, value1], [key2, value2], ...]. This will give you something that looks like this:
[
["0", {"id"=>"1", "add_asset"=>"0"}],
["1", {"id"=>"2", "add_asset"=>"0"}],
["2", {"id"=>"3", "add_asset"=>"1"}]
]
So:
Why is it failing to read record "0" then successfully reading record "1"?
It isn't. It's failing all three times, it's just one failure happens to look correct.
The first iteration, i is 0 and check is equal to ["0", {"id"=>"1", "add_asset"=>"0"}], your block accesses check[0] which is "0". You then check "0"["id"] and "0"["add_asset"], which are both nil.
On the next iteration, i is 1 and check is ["1", {"id"=>"2", "add_asset"=>"0"}]. The block accesses check[1] and gets {"id"=>"2", "add_asset"=>"0"} purely by coincidence, and things seem to work.
Why is it bombing completely on record "2"?
On the third iteration, the block gets an i of 2 and check of ["2", {"id"=>"3", "add_asset"=>"1"}]. That array has no [2], so you get nil, and then your block attempts to access nil["add"] which fails.

Answer 2

In Ruby there is a difference between a hash and an array. Hashes can have nearly anything as a key. An array accepts only an integer. Your hashes are built with strings for keys. Decompose like this:
assets = {"0"=>{"id"=>"1", "add_asset"=>"0"},
"1"=>{"id"=>"2", "add_asset"=>"0"},
"2"=>{"id"=>"3", "add_asset"=>"1"}}
assets.each do |key, val|
puts "key = #{key}"
val.each do |inner_key, inner_val|
puts " key=#{inner_key} val=#{inner_val}"
end
end
Output:
key = 0
key=id val=1
key=add_asset val=0
key = 1
key=id val=2
key=add_asset val=0
key = 2
key=id val=3
key=add_asset val=1