Helper method to use Postgres' COPY with ActiveRecord

copy_from_client.rb

# Put this in config/initializers/copy_from_client.rb

class CopyFromClientHelper
  attr_reader :count

  def initialize(conn, column_types)
    @count = 0
    @conn = conn
    @column_types = column_types
  end

  def <<(row)
    row = row.map.with_index { |val, idx| @column_types[idx].type_cast_for_database(val) }
    @conn.put_copy_data(row)
    @count += 1
  end
end

module CopyFromClient
  def self.copy_from_client(columns, &block)
    conn         = connection.raw_connection
    column_types = columns.map { |c| columns_hash[c.to_s] }
    helper = CopyFromClientHelper.new(conn, column_types)
    conn.copy_data %{COPY #{quoted_table_name}("#{columns.join('","')}") FROM STDIN}, PG::TextEncoder::CopyRow.new do
      block.call helper
    end
    helper.count
  end
end

if defined?(ActiveRecord::Base)
  ActiveRecord::Base.send(:include, CopyFromClient)
end

example.rb

MyModel.copy_from_client [:column1, :column2, :column3] do |copy|
  copy << ['abc', 123, { json: 'is supported' }]
end