Can I create an on-chain view that calls another contract's on-chain view and return it?

Question

I have two contracts contract_one and contract_two. On contract_two I have an on-chain-view defined like this:

@sp.onchain_view()
def get(self, id):
    sp.result(self.data.map[id])

This view works correctly. Now what I want is to call this view from contract_one. Here's what I've tried:

@sp.onchain_view()
def get(self, id):
    contract_address = sp.local("contract_address", sp.address('CONTRACT_ONE_ADDRESS'))
    result = sp.local("result", sp.view("get", contract_address.value, id, t = sp.TRecord( data = sp.TString, address = sp.TAddress )).open_some("Invalid view"))
    sp.result(result.value)

Although the contract is compiled successfully, I cannot originate it to hangzhounet, getting the following error:

 "Http error response: (400) Failed to parse the request body: No case matched:\n...

The error then lists several /kind reasons.

My question is, what I'm trying to do, is it possible to achieve? Is there another way to do this? My final goal is to call this view with Taquito and get a result.

Answer 1

Not too familiar with SmartPy, but this is exactly what onchain views are supposed to do, so it should work. My best guess (again, I'm a ligo developer and have very little knowledge of SmartPy), is that the @sp.onchain_view() decorator in contract_one should be replaced by @sp.entry_point, as the get function in contract_one is an entrypoint calling an onchain view, and not a view function. See this example of calling an onchain view in the smartpy docs: https://smartpy.io/docs/general/views/#examples-1

Answer 2

Yes, you can create it. Here is a small working example of what you are trying to do.

import smartpy as sp


class contract_two(sp.Contract):
    def __init__(self):
        self.init(
            _map = sp.map({
                0: sp.record(
                    data = 'data',
                    address = sp.address('tz1burnburnburnburnburnburnburjAYjjX')
                )
            })
        )

    @sp.onchain_view()
    def get(self, id):
        sp.result(self.data._map[id])


class contract_one(sp.Contract):
    def __init__(self, contract_two_address):
        self.init(
            contract_two_address = contract_two_address
        )

    @sp.onchain_view()
    def get(self, id):
        result = sp.view(
            "get",
            self.data.contract_two_address,
            id,
            t = sp.TRecord( data = sp.TString, address = sp.TAddress )
        ).open_some("Invalid view")
        sp.result(result)


@sp.add_test(name = 'Test')
def test():
    scenario = sp.test_scenario()
    admin = sp.test_account('admin')

    c2 = contract_two()
    scenario += c2
    c1 = contract_one(c2.address)
    scenario += c1

    result = c1.get(0)
    scenario.show(result)

Few things to note:

• Use _map instead of map, because it conflicts with Python's methods.
• When you are deploying the contract_one, make sure to write a valid contract address instead of CONTRACT_ONE_ADDRESS
• And, that contract should have this on-chain view you're trying to call.
• I can't conclude the exact cause of the /kind error because I'll need the complete log for that.
• No need to define local variables (at least in the example that you've given).
• If you face difficulty calling it with Taquito, raise a separate question. Will try to help with Taquito there :)