gistfile1.rb

# First thing we need is the raw connection to our database. ActiveRecord makes this quite easy...
pg_connection = ModelName.connection.raw_connection

# Next, tell PG that we're going to be copying a boat load of data into model_names...
pg_connection.exec "COPY model_names (field_a, field_b, field_c) FROM STDIN"

# Process our file line-by-line 
IO.foreach("path/to/file.tsv", "r") do |line|
  
  # Convert our tab-delimited string into an array
  raw_fields = line.split("\t")  
  
  # and re-combine it back into a tab-delmited string, but only using the fields we need, wrapping any fields in quotes that we need
  new_row = [raw_fields[0], "'#{raw_fields[5]}'", raw_fields[21]].join("\t")

  # send the data to our database
  pg_connection.put_copy_data(new_row + "\n")
end

# And finally, tell PG that we're done inserting data.
pg_connection.put_copy_end