Specifying a signatory from another contract

Question

In Daml, I have setup an Agent contract. This is its down Agent.daml file. I then have a proposal contract (Proposal.daml), in which I imported the Agent module. I wanted to specify agentname is the signatory for the proposal contract, but compiler tells me that no such party exists.

There are no parties in my Proposal contract which is why I chose a party from another contract. I'm not sure how to solve this?

This is the agent contract

module Agent where


-- MAIN_TEMPLATE_BEGIN
template Agent with
  agentname: Party
  guarantors: [Party]
where

  signatory agentname
  observer guarantors

And this is the Proposal contract

module Proposal where

import Agent

-- MAIN_TEMPLATE_BEGIN
template Proposal with

  projectdescription: Text
  unitsrequired: Int
  marketingcost: Int
  distributioncost: Int
  additionalcost: Int

where
  signatory agentname
  observer guarantors

-- MAIN_TEMPLATE_END

     key agentname: Party   
     maintainer key

Answer 1

The signatories of a contract need to be computable from the contract arguments. You can't reference another contract by ContractId and get them from there. The reason is that that other contract might be archived, in which case you suddenly have a contract for which the signatories can't be read.

So your Proposal must contain the agent that is making the proposal:

template Proposal with
  agent : Party
  projectdescription: Text
  unitsrequired: Int
  marketingcost: Int
  distributioncost: Int
  additionalcost: Int
where
  signatory agent
  ...

As a little aside: Party is not in general a human-readable string so best not to use them as "names". If you want a human-readable name, add a name : Text field to Agent.

Now you may wonder: How do I enforce the constraint that for every Proposal there exists an Agent? There's a long and informative thread on that topic on the Daml forums.