Acess variables in DAML template like in an object

Question

Okay am new to DAML and have extensive Java programming experience. Now, I have a question. In Java, 'Class A' has 'Class B', and like this, A can use 'state' of 'Class B'. I want to do something like this in DAML too.

If I think template as a class, 'contract id' is an instance of it, and the 'state' of the template (the things we declare in 'with') should be accessible in another template when passed in as a parameter, but I get compilation errors in the code I wrote.

One way to proceed is to send 'party' as a parameter instead of contract ID, and then try to access the party in contract, but I wanted to check if/ what is wrong with this!

Thanks in advance!

First template

daml 1.2
module RFP where

template RFP
with
        requestorCEO: Party
    where
        signatory requestorCEO

Second template

daml 1.2

module InternalComm where

import RFP

template InternalComm 
    with
        -- RFP is sent in as a parameter to this template.
        rfpContractID: ContractId RFP
    where
        -- Here with this, I'm trying to say that the CEO who would be approving 
        -- an RFP is the signatory for internal communications too. It is the
        -- below line that fails with compilation error.
        signatory rfpContractID.requestorCEO

This is the actual error message I get for aforementioned problem. Any thoughts would be greatly appreciated!

No instance for (DA.Internal.Record.HasField
                         "requestorCEO" (ContractId RFP) a0)

score 1 · Accepted Answer · answered Jun 29 '19 at 10:23

In DAML the RFP template gives you a type RFP on which you can project out the fields (just like Java), and a type ContractId RFP which is more like a pointer to the contract on the ledger. You can "dereference" the ContractId to get the RFP using the function fetch. However, that function runs in an Update, so can't be called from a signatory. I suspect you need to change InternalComm to take a RFP without the ContractId wrapper.

score 0 · Answer 2 · answered Jul 01 '19 at 07:27

This is how it worked - just remove ContractId from whole of the template.

module InternalComm where

import RFP

template InternalComm 
    with
        -- ContractId to be removed from below line, and compilation error is resolved.
        -- rfpContractID: ContractId RFP
        rfpContractID: RFP
    where
        signatory rfpContractID.requestorCEO

Acess variables in DAML template like in an object

2 Answers2