How to Return an Array of structs from Solidity?

Question

i'm having an issue when trying to return an array of structs from a getter function i've made.

The smart contract is an ERC721 Staking Contract.

This is the getter function:

function getNftInfo(uint256[] calldata tokenIds) public view returns (uint256[] memory){
     
      uint256 tokenId;
      uint256[] memory tmp = new uint256[](tokenIds.length);
      for (uint i = 0; i < tokenIds.length; i++) {
          tokenId = tokenIds[i];
          Stake storage staked = vault[tokenId];
          tmp[i] = staked;
      }

      return tmp;
  }

This is the struct and the mapping:

 struct Stake {
        uint256 tokenId;
        uint256 lockPeriod;
        uint256 startDate;
        address owner;
    }
   
    mapping(uint256 => Stake) public vault;

When a user insert the staked tokenIds (ex. [1,345,10]) the return should be =>

[
  {1, lockperiod,StartDate,owner},
  {245, lockperiod,StartDate,owner},
  {10, lockperiod,StartDate,owner},
]
```
Someone could help me please?
Thank you

Naren Murali · Accepted Answer · 2022-07-12T10:01:39.433

We cannot get an array of structs currently in solidity as far as I have checked around on the internet, instead return an array of individual properties of the struct and access using their index ( as a workaround ). Kindly refer this answer also.

// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.7.0 <0.9.0;

/**
 * @title Storage
 * @dev Store & retrieve value in a variable
 * @custom:dev-run-script ./scripts/deploy_with_ethers.ts
 */
contract Storage {
    struct Stake {
        uint256 tokenId;
        uint256 lockPeriod;
        uint256 startDate;
        address owner;
    }
   
    mapping(uint256 => Stake) public vault; 

    function loadData(uint256 tokenId, uint256 lockPeriod, uint256 startDate, address owner) public {
        Stake memory newStake = Stake(tokenId, lockPeriod, startDate, owner);
        vault[tokenId] = newStake;
    }
    
    function getNftInfo(uint256[] calldata tokenIdsInput) public view returns (uint256[] memory tokenIdsReturn,
        uint256[] memory lockPeriodsReturn,
        uint256[] memory startDatesReturn,
        address[] memory ownersReturn){
      uint256 tokenId;
      uint256[] memory tokenIds = new uint256[](tokenIdsInput.length);
      uint256[] memory lockPeriods = new uint256[](tokenIdsInput.length);
      uint256[] memory startDates = new uint256[](tokenIdsInput.length);
      address[] memory owners = new address[](tokenIdsInput.length);
      for (uint i = 0; i < tokenIdsInput.length; i++) {
          tokenId = tokenIdsInput[i];
          Stake storage staked = vault[tokenId];
          tokenIds[i] = staked.tokenId;
          lockPeriods[i] = staked.lockPeriod;
          startDates[i] = staked.startDate;
          owners[i] = staked.owner;
      }

      return (tokenIds,
        lockPeriods,
        startDates,
        owners);
  }
}

that's the output for insert [1,2]: it seems only an array with index 0 with the 2 answer concatenated { "0": "tuple(uint256,uint256,uint256,address)[]: 1,1657616003,1657615943,0xAb8483F64d9C6d1EcF9b849Ae677dD3315835cb2,2,1657616003,1657615943,0xAb8483F64d9C6d1EcF9b849Ae677dD3315835cb2" } — Pietro Ciattaglia, Jul 12 '22 at 08:54
I had a similiar issue with the formatting of remix. Can you try to use openzeppelin defender to see the result from the view? — sirroger, Jul 13 '22 at 06:12

How to Return an Array of structs from Solidity?

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