Reversible migration for change_column_default from not having any default in Rails

Question

The Rails guides to active record migrations says that you can do

change_column_default :products, :approved, from: true, to: false

I\'ve got a

Answer 1

Just to add a few points. If you are stuck with the Rails version not supporting reversible change_column_default, one option to get past the problem is:

def change
    # If your dataset is small, just cache in memory, if large, consider file dump here:
    cache = Table.all
    # Full column def important for reversibility
    remove_column :table, :column, :type, { config_hash }
    # Re-add the column with new default:
    add_column  :table, :column, :type, { config_hash, default: 0 }
    # Now update the data with cached records (there might be more efficient ways, of course):
    cache.each do |rec|
        Table.find(rec.id).update(column: rec.column)
    end
end