Solidity Event Data – How to Decode Event Data with Struct in Solidity

abiethers.jssolidity

I need to retrieve data to front end from event:

eventSignature: 'ProposalIsCreated(bytes32,address,address,address,string,uint256,uint256,bytes32))'

I use defaultAbiCoder from ethers.js and this function throws an error, probably because I use array syntax, but I have no other ideas how to represent struct and make it work:

ethers.utils.defaultAbiCoder.decode(
    [
      "bytes32",
      "address",
      ["address", "address", "string", "uint256", "uint256", "bytes32"],
    ],
    event.data
  );

Data example:

"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"

Best Answer

you can do it this way your

//rpc
const connection = new ethers.providers.JsonRpcProvider('https://rpc-mumbai.maticvigil.com/', { chainId: 80001 });

//set address
let contractAddress = "address";
   //set private-key
   const privateKey="key";
 
 //connect wallet
 var signer = new ethers.Wallet(privateKey, connection)
 //create signer
 const txSigner = contract.connect(signer);

 //instance of struct
 const Ranger = "(uint256 idNumber,uint256 dateOfBirth,string lastName,string userAddress,string gender,string  firstName,string middleName,uint256 accountNumber,bool isActive,uint256 phone; )";

//human readable abi
const ABI = [
 `function addRanger(uint256 _id,string _userAdd,string  _gender,uint256 _dob,uint _phone,string _middleName,string _firstName,string _lastName,uint256  _account) public`,
`function getAllUsers() public`,
`event AddedRanger(${Ranger}  created)`];

 //create contract instance
const contract = new ethers.Contract(contractAddress, ABI, connection);

 contract.on("AddedRanger",(Ranger,event) => {
        console.log({
            value: Ranger.toString(),
            data: event
        });
    });

Related Solutions

Solidity Arrays – How to Refer to a Struct within an Array

Short Answer

Q1: Yes, it's a valid approach.

Q2: You better have a look at this. I can't describe it any better: http://vessenes.com/solidity-frustrations-references-and-mapping/

Best Answer

Exercise caution.

Detailed Answer

This initiated an interesting side conversation.

A colleague suggested this heuristic:

If the variable points to a specific slot in the storage, then it's not by reference. If it points to somewhere that needs further direction, then it is by reference.

I would take that to mean structs, mappings, arrays; anything with a [key] leads to a reference variable.

A test/demonstration shows how these references can have an impact on arrays; possibly updating something that wasn't supposed to be/expected to be updated. Obviously, updating storage with values that aren't supposed to be there can have non-trivial consequences.

The first example maps closely to your question code example. The second comes from some exploratory testing. Both are doing non-obvious updates to array storage through reference variables.

pragma solidity ^0.4.6;

contract Reference {

  struct NumberStruct {
    uint number;
    bool isCurrent;
  }

  NumberStruct[] nums;

  function Reference() {
    NumberStruct memory numberStruct;
    nums.push(numberStruct);
  }

  function setTwo() {
    var aNumberStruct = nums[0];
    // these references are writing to nums[]
    aNumberStruct.number = 2;
    aNumberStruct.isCurrent = true;
  }

  function getSlotZero() 
    constant
    returns(uint number, bool isCurrent) 
  {
    // you get 2, true after setTwo() and 0, false before setTwo()
    return(nums[0].number, nums[0].isCurrent)    ;
  }
}

// simplified example

contract Test {

  byte[20] v;

  function set() {
    var v1 = v;
    v1[0] = 1;
    // we have changed v[0]
  }

  function get() constant returns(byte value) {
    return(v[0]);
  }

}

Hope it helps.

Solidity – How to Solve ‘TypeError: Internal or Recursive Type is Not Allowed for Public State Variables’

mapping(address => AllUserStakedTimestamp) public allUserStakes;

struct AllUserStakedTimestamp {
    bool[] _wasUnstaked;
    bool[] _autoRenewal;
    uint[] _amountStaked;
    uint[] _timeOfStake;
    uint[] _timesOfRelease;
    uint[] _optionReleaseSelected; // 0-1-2
    uint[] _epochDuration;
    uint[] _rewardPerCycle;
    uint[] _finalStakeReward;
}

That will do. There you have to give public instead of internal.

Just know there are four types of function visibility in the solidity:

Public
Private
Internal
External.

Public: The function can be called by anyone both from inside the contract and outside the contract.

Private: The function is only available inside the contract. When you assign this visbility, the function isn't even available to inherit.

Internal: Just like the private but it supports inheritance. You can inherit the function.

External: Function can only be accessed by outside the contract. If the function visibility is external, that means it is not accessable internally.

You can read more about the function visibilities here.

Tell me if it helps!

Best Answer

Related Solutions

Solidity Arrays – How to Refer to a Struct within an Array

Solidity – How to Solve ‘TypeError: Internal or Recursive Type is Not Allowed for Public State Variables’

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