how to access to a public mapping from test script

Question

i'm in hardhat i'v this public mapping

    mapping (address user => uint[] commentIds) public userComments;

and i'm trying to call it inside my test Script

        console.log(`user1 comments:  ${await postContract.userComments(user1.address)}`);

i get this error Error: no matching fragment (operation="fragment", info={ "args": [ "0x70997970C51812dc3A010C7d01b50e0d17dc79C8" ], "key": "userComments" }, code=UNSUPPORTED_OPERATION, version=6.8.0)

**i can access to the mapping by create a getter function but why is that isn't that public modifier already do that under the hood **

Answer 1

If you are accessing a mapping that is some type to an array type, you need to pass the array index that you'd like to access as well.

For example: access first element in the returned list

console.log(`user1 comments:  ${await postContract.userComments(user1.address, 0)}`);

Why? well, if you check abi of your contract, the userComments will have two parameters. address, and uint (this is the index of returned list at given address)