What's the correct way to read an array from a csv field in Ruby? - ruby

Question

I am trying to save some class objects to a csv file, everything works fine. I can save and read back from the csv file, there is only a 'minor' problem with an attribute that is an Array of Strings.
When I save it to the file it appears like this: "[""Dan Brown""]"
CSV.open('documents.csv', "w") do |csv|
csv << %w[ISBN Titre Auteurs Type Disponibilité]
#docs.each { |doc|
csv << [doc.isbn, doc.titre, doc.auteurs, doc.type, doc.empruntable ? "Disponible" : "Emprunté"]
}
end
And when I try to extract the data from the file I end up with something like this: ["[\"Dan Brown\"]"].
table = CSV.parse(File.read("documents.csv"), headers: true)
table.each do |row|
doc = Document.new(row['Titre'], row['ISBN'], row['Type'])
doc.auteurs << row['Auteurs'] #This the array where there is a 'problem'
if row['Disponibilité'] == "Disponible"
doc.empruntable = true
else
doc.empruntable = false
end
#docs.push(doc) #this an array where I save my objects
end
I tried many things to solve this but without any luck. I would be thankful if you can help me find a solution.

Answer 1

Since a CSV file, by it's nature, contains in its fields only strings, not arrays or other data types, the CSV class is applying the to_s method of the objects to turn them into a string before putting them into the CSV.
When you later read them back, you just get this - the string representation of what once had been your array. The only one who knows that 'Auteurs' should end up as an array of strings, is the application, i.e. you.
Hence on reading the CSV, after having extracted the autheurs string, you need to convert it manually back to an Array, because there is no automatic "inverse method" to reverse the to_s.
A cheap, but dangerous way to do it, is to use eval, which indeed would reconstruct your array. However, you need to be sure that nobody had a chance to fiddle manually with the CSV data, because an eval allows sneaking in arbitrary code.
A safer way would be to either write your own conversion function to and from String representation, or use a format such as YAML or JSON for representing the Array as String, instead of using to_s.