Error while generating smart contracts which returns array of struct in Web3j v3 3 1

Question

pragma solidity ^0.4.21;

pragma experimental ABIEncoderV2;

function getPurchaseOrderForVendor(string vendorNameInput) constant returns (PurchaseOrderStruct[])

I am returning an array of struct from solidity function as given above. It is compiled to abi and bin files. The issue is with creating wrapper files for the contract using web3j(v3.3.1). I'm getting the below errors:

Generating com.contract.InvoiceSettlement_sol_InvoiceSettlement ... 
Exception in thread "main" java.lang.UnsupportedOperationException: 
Unsupported type
encountered: tuple
    at org.web3j.abi.datatypes.generated.AbiTypes.getType(AbiTypes.java:221)

    at org.web3j.codegen.SolidityFunctionWrapper.buildTypeName(SolidityFunct
ionWrapper.java:851)

Answer 1

Solidity does not support returning structs in external calls. It is only allowed in internal function calls. You need to decompose the struct and return the elements via a tuple.

You need to either return strings as bytes32, or (my preferred approach) you use one function to return the size of the array you want and have your retrieval function take in an index parameter and return one decomposed struct element at a time.