Feb 21, 2008

Create Structured Data in Migrations

Occasionally I'll decide to create some structured data in a migration by issuing create statements against my model classes. In a project I'm currently working on, I had to do this several levels deep. Rather than using temporary variables to create the sub items and so-on, all in a lexically flat structure, I came up with this simple one-liner:

def self.with(o); yield o; end

Doing this now allows me to issue those creates with nested data as a series of nested blocks, which is looks much better. For example:

with ChordQuality.create(:name => 'Major', :code => 'MAJ') do |q|
  with q.chords.create(:name => 'Major Triad') do |c|
    c.chord_symbols.create(:name => 'maj')
    c.chord_symbols.create(:name => 'M', :case_sensitive => true)
  end
  with q.chords.create(:name => 'Major 7') do |c|
    c.chord_symbols.create(:name => 'maj7')
    c.chord_symbols.create(:name => 'M7', :case_sensitive => true)
    with c.children.create(:name => 'Major 7 #11') do |cc|
      cc.chord_symbols.create(:name => 'maj7#11')
      cc.chord_symbols.create(:name => 'M7#11')
      cc.chord_symbols.create(:name => 'lyd')
      cc.chord_symbols.create(:name => 'lydian')
    end
  end

  with q.chords.create(:name => 'Major 6') do |c|
    c.chord_symbols.create(:name => 'maj6')
    c.chord_symbols.create(:name => 'M6', :case_sensitive => true)
  end
end

Oh, the beauty of Ruby code blocks!

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