Ruby-on-rails – Rails – How to save a hash to the DB and using it as a hash once you pull it form the DB (not pulling it as a sting)

hashrubyruby-on-railsruby-on-rails-4

If I save a hash to the DB

hash_value = {"1"=>"val1", "2"=>"val2", "3"=>"val3", "4"=>"val4"}
@page.update(hash: hash_value)

Then try and loop through each key of the hash on the page page

hash = @page.hash 

<%= hash.each do |key, value| %>

 <%= value %>

<% end %>

I get the error undefined method 'each' for #<String:0x007fdda1d8b568>. This error made me realise it is saved saved as a string to the DB.

How do I make it save as a hash so when I pull it rom the DB it is in a hash not a string? Doing some research I found serialize but I cant make out how to use it properly. Is it used to change the DB table to have all values saved in that table be hashes? If so what is added in the migration file to do that?

    create_table :pages do |t|

      t.timestamps null: false
      t.text  :title
      t.text  :content_top
      t.text  :content_bottom
      t.text  :hash

      t.timestamps null: false
    end

Just confused as to how saving a hash to the DB and calling it as a hash is accomplished.

Best Answer

The column type for :hash on :pages table is text, which is the correct column type to use when you wish for a column to store a hash. You must now also indicate on the Page model that you wish to serialize this column. Something like this:

class Page < ActiveRecord::Base
  serialize :hash

Then you can attempt to test your new setup like this:

@page = Page.new
@page.hash = {"1"=>"val1", "2"=>"val2", "3"=>"val3", "4"=>"val4"}
@page.save

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Here's an example:

class RenameOldTableToNewTable < ActiveRecord::Migration
  def self.up
    rename_table :old_table_name, :new_table_name
  end

  def self.down
    rename_table :new_table_name, :old_table_name
  end
end

I had to go and rename the model declaration file manually.

Edit:

In Rails 3.1 & 4, ActiveRecord::Migration::CommandRecorder knows how to reverse rename_table migrations, so you can do this:

class RenameOldTableToNewTable < ActiveRecord::Migration
  def change
    rename_table :old_table_name, :new_table_name
  end 
end

(You still have to go through and manually rename your files.)

Ruby – How to add an array to another array in Ruby and not end up with a multi-dimensional result

You've got a workable idea, but the #flatten! is in the wrong place -- it flattens its receiver, so you could use it to turn [1, 2, ['foo', 'bar']] into [1,2,'foo','bar'].

I'm doubtless forgetting some approaches, but you can concatenate:

a1.concat a2
a1 + a2              # creates a new array, as does a1 += a2

or prepend/append:

a1.push(*a2)         # note the asterisk
a2.unshift(*a1)      # note the asterisk, and that a2 is the receiver

or splice:

a1[a1.length, 0] = a2
a1[a1.length..0] = a2
a1.insert(a1.length, *a2)

or append and flatten:

(a1 << a2).flatten!  # a call to #flatten instead would return a new array

Best Answer

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