custom_changeset.rb

#!/usr/bin/env ruby
require "rom-sql"
require "rom-repository"
require "dry-types"

module Relations
  class Users < ROM::Relation[:sql]
    schema(:users, infer: true)
  end

  class Participants < ROM::Relation[:sql]
    schema(:participants, infer: true)
  end
end

module Repositories
  class Users < ROM::Repository[:users]
  end

  class Participants < ROM::Repository[:participants]
  end
end

config = ROM::Configuration.new(:sql, "sqlite::memory")

config.gateways[:default].tap do |gateway|
  migration = gateway.migration do
    change do
      create_table :users do
        primary_key :id
        column :name, String
        column :activated_at, Time
      end

      create_table :participants do
        primary_key :id
        string :name, null: true
        column :activated_at, Time
      end
    end
  end

  migration.apply gateway.connection, :up
end

class CreateChangeset < ROM::Changeset::Create
  map do |tuple|
    tuple.merge(activated_at: Time.now)
  end
end

config.register_relation Relations::Users
config.register_relation Relations::Participants
container = ROM.container(config)

user_repo = Repositories::Users.new(container)
participant_repo = Repositories::Participants.new(container)

puts user_repo.changeset(CreateChangeset).data(name: 'Jane').commit.inspect
# #<ROM::Struct[User] id=1 name="Jane" activated_at=2017-02-02 11:39:45 +0100>
puts participant_repo.changeset(CreateChangeset).data(name: 'Jane').commit.inspect
# #<ROM::Struct[Participant] id=1 name="Jane" activated_at=2017-02-02 11:39:45 +0100>