How to call prefixed by trait(interface) methods using the polkadot api?

Question

I wrote a smart contract, implementing a psp34 token (docs). Inside the smart contract, it is no problem using the methods provided by openbrush. However, when I deploy it on chain and want to call a method (like for example owner_of), using the pokadot{.js} api, I run into the following problem:

When looking at the metadata of my contract, a typical method looks like this:

{
      "args": [
        {
          "label": "id",
          "type": {
            "displayName": [
              "Vec"
            ],
            "type": 7
          }
        }
      ],
      "docs": [
        " Returns the owner of a token."
      ],
      "label": "owner_of",
      "mutates": false,
      "payable": false,
      "returnType": {
        "displayName": [
          "Option"
        ],
        "type": 24
      },
      "selector": "..."
    },

But a method from the openbrush looks like this:

{
      "args": [
        {
          "label": "id",
          "type": {
            "displayName": [
              "psp34_external",
              "OwnerOfInput1"
            ],
            "type": 1
          }
        }
      ],
      "docs": [
        " Returns the owner of the token if any."
      ],
      "label": "PSP34::owner_of",
      "mutates": false,
      "payable": false,
      "returnType": {
        "displayName": [
          "psp34_external",
          "OwnerOfOutput"
        ],
        "type": 24
      },
      "selector": "..."
    }

From my understanding the polkadot api changes the label from 'owner_of' to 'ownerOf'. But what does it to 'PSP34::owner_of'?

I tried to call the original PSP34 owner_of method like this:

const { gasRequired, storageDeposit, result, output } = await contract.query.ownerOf(
    accountId,
    {
    gasLimit,
    storageDepositLimit,
    },
    id
)

But it does gives the error 'ownerOf is not a function'. My solution so far was to just implement a method in my contract which calls on the PSP34 owner_of method, and to then call this new method with the API.

Although this works, it strikes me as not pretty. Especially, since the original PSP34 owner_of method is still visible on chain.

My question now is: Is it possible to call the PSP34::owner_of method with the polkadot api? And if not, how can I overwrite the method so only the method in my contract is visible to the chain and I can call it with the polkadot api like before.

Answer 1

PSP34 in the rust level is a trait(interface) implemented by your contract. At the ABI level is a prefix or a namespace of the method that makes it unique. It allows supporting several methods with the same naming but with different prefixes.

// First
impl Contract {
    #[ink(message)]
    pub fn balance_of(&self, owner: AccountId) -> Balance { ... }
}

// Second
impl PSP22 for Contract {
    #[ink(message)]
    pub fn balance_of(&self, owner: AccountId) -> Balance { ... }
}

// Third
impl PSP34 for Contract {
    #[ink(message)]
    pub fn balance_of(&self, owner: AccountId) -> Balance { ... }
}

All those three implementations will generate different labels and selectors(selector is 4 bytes of the black2b hash of the label) for your methods:

• First: "label": "balance_of", "selector": "0x0f755a56"
• Second: "label": "PSP22::balance_of", "selector": "0x6568382f"
• Third: "label": "PSP34::balance_of", "selector": "0xcde7e55f"

The polkadot-js can work with prefix and non-prefixed methods. It campelCase prefix and name of the method.

• First: contract.query.balanceOf or contract.query["balanceOf"]
• Second: contract.query["psp22::balanceOf"]
• Third: contract.query["psp34::balanceOf"]

The same works for the tx namespace. Maybe it can be changed in the future after resolving issue.

It should solve your problem=) But I suggest you try typechain-polkadot for integration tests and frontend development. It will generate all classes based on the ABI of your contract, and you will know how to call each method.