Sequel migration - only add column if table does not have it yet

Question

I am trying to create a Sequel migration that goes through a list of tables, and try to add a specific column if the table does not of that column yet.

For example:

Sequel.migration do
  change do
    table_list = [:table1, :table2, :table3]

    table_list.each do |t|
      if t does not have :specific_column yet
        alter_table(t) do
          add_column :sepcific_column, type: String
        end
      end
    end
  end
end

Is is possible to tell if the column already exist in a table, so I can do stuff accordingly?

Answer 1

Yes, it is possible. The method Dataset#columns returns a list of columns. This result can be used to be checked with include?

Full example:

Sequel.migration do
  change do
    table_list = [:table1, :table2, :table3]

    table_list.each do |t|
      if ! self[t].columns.include?(:specific_column)
        alter_table(t) do
          add_column :specific_column, type: String
        end
      end
    end
  end
end

or

Sequel.migration do
  change do
    table_list = [:table1, :table2, :table3]

    table_list.each do |t|
        alter_table(t) do
          add_column :specific_column, type: String
        end unless self[t].columns.include?(:specific_column)
      end
    end
  end
end