NEAR智能合约调用报错：cannot read property 'prefix' of undefined

错误信息 #

调用buy方法时触发以下执行错误：

ExecutionError: "Smart contract panicked: cannot read property 'prefix' of undefined" +
      '    at reconstruct (build/microsoft.js:994)
' +
      '    at _reconstruct (build/microsoft.js:1102)
' +
      '    at buy (build/microsoft.js:1137)
'

原合约代码 #

import { NearBindgen, call, view, UnorderedMap, initialize } from 'near-sdk-js';

@NearBindgen({})
export class ExchangeContractMicrosoft {
  private stocks: UnorderedMap<number> = new UnorderedMap<number>(
    'unique-id-map1',
  );

  constructor() {
    this.stocks.set('msft', 10000000);
  }

  @call({})
  buy(): void {
    const stock: string = 'msft';
    this.checkStock(stock, 1);
    this.stocks.set('msft', this.stocks.get(stock) - 1);
  }

  private checkStock(stock: string, value: number): void {
    if (this.stocks.get(stock) < value) {
      throw 'Not enough stocks';
    }
  }
}

交互命令 #

near call sipars.testnet buy '{}'  --accountId sipars.testnet --gas=300000000000000

问题原因及修复方案 #

问题根源 #

NEAR SDK-JS不支持通过类的构造函数初始化合约状态，构造函数不会在合约部署时被正确执行，导致stocks这个UnorderedMap未被实例化，调用buy方法时访问其属性就会触发undefined错误。

修复步骤 #

1. 移除构造函数，改用带@initialize()装饰器的初始化方法承载状态初始化逻辑
2. 先声明stocks属性，在初始化方法中完成实例化和初始值设置
3. 部署新合约后，必须先调用初始化方法完成状态初始化

修复后的合约代码：

import { NearBindgen, call, view, UnorderedMap, initialize } from 'near-sdk-js';

@NearBindgen({})
export class ExchangeContractMicrosoft {
  private stocks: UnorderedMap<number>;

  @initialize({})
  init(): void {
    this.stocks = new UnorderedMap<number>('unique-id-map1');
    this.stocks.set('msft', 10000000);
  }

  @call({})
  buy(): void {
    const stock: string = 'msft';
    this.checkStock(stock, 1);
    this.stocks.set('msft', this.stocks.get(stock) - 1);
  }

  private checkStock(stock: string, value: number): void {
    if (this.stocks.get(stock) < value) {
      throw 'Not enough stocks';
    }
  }
}

后续操作 #

部署修复后的合约后，先执行初始化命令：

near call sipars.testnet init '{}' --accountId sipars.testnet

之后再调用buy方法即可正常执行。

内容的提问来源于stack exchange，提问作者Parshant Singh