Making contracts and parties visible to a party

Hi,

I have a situation where the operator party creates the network and on-boards a bunch of seller and buyer parties. I need the buyers to fetch / see all sellers (for the purposes of sending a Request for Quotation to one or more of them). How would I achieve that?

Many thanks!

There is the Fetch All Known Parties JSON API endpoint, but that is not exactly what you need:
https://docs.daml.com/json-api/index.html#fetch-all-known-parties

You can also create a non-consuming choice that returns all sellers that the party specified as the choice argument can deal with.

exerciseResult field on the response will contain the sellers that the choice returned:
https://docs.daml.com/json-api/index.html#exercise-response

You will have to model the buyer-seller relationship in your DAML.

Thanks Leonid. I guess my question is about how to create that buyer-seller relationship since they are both onboarded by the operator.

I thought of maintaining a list of all buyers and then adding them as observers on the SellerRole contract when a seller is onboarded (and then add every new buyer when one is onboarded). That sounds pretty cumbersome though so looking for a better answer.

@ManishGrover how about something like this

module Main where

template Exchange
  with
    operator: Party
    buyers: [Party]
    sellers: [Party]
  where
    signatory operator
    observer buyers
    
    nonconsuming choice AllSellers: [Party] with
        buyer: Party
      controller buyer
        do
          assert (buyer `elem` buyers)
          return sellers

setup : Scenario [Party]
setup = scenario do
  exchangeOperator <- getParty "ExchangeOperator"
  buyer1 <- getParty "Buyer1"
  buyer2 <- getParty "Buyer2"
  buyer3 <- getParty "Buyer3"
  seller1 <- getParty "Seller1"
  seller2 <- getParty "Seller2"
  seller3 <- getParty "Seller3"

  exchange <- submit exchangeOperator do
    create Exchange with
      operator = exchangeOperator
      buyers = [buyer1, buyer2]
      sellers = [seller1, seller2, seller3]

  -- buyer3 is not registered, so they can't see sellers
  submitMustFail buyer3 do
    exercise exchange AllSellers with buyer = buyer3

  submit buyer1 do
    exercise exchange AllSellers with buyer = buyer1

@Leonid_Shlyapnikov’s example shows one way, where you create some sort of registry contract. In his example you wouldn’t even need the nonconsuming choice to get the sellers - the buyers are observers so would simply see the Exchange contract.

If you don’t want to disclose buyers amongst each other, then you don’t get around maintaining a contract per buyer. You could, for example, add the seller to each buyer role contract when the seller is onboarded. You mention this is cumbersome but if you key your buyer role contracts it can be done in the same, single onboarding transaction.