如何与实体结构的映射映射交互?

Question

我创建了嵌套映射的结构体。考虑下面这段用solididity写在合约中的代码:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.4;
contract TestContract {
struct Item {
uint itemId;
uint itemValue;
}
struct OverlayingItemStruct {
mapping(uint => Item) items;
uint overlayingId;
uint itemsCount;
}
mapping(uint => OverlayingItemStruct) public overlayingItems;
uint public overlayCount;
function addOverlayingItemsStruct(uint _value) external {
overlayCount ++;
mapping(uint => Item) memory items;
items[1] = Item(1, _value);
overlayingItems[overlayCount] = OverlayingItemStruct(items, 1, 1);
}
function addItem(uint _value, uint _overlayId) external {
OverlayingItemStruct storage overlay = overlayingItems[_overlayId];
overlay.itemsCount ++;
overlay.items[overlay.itemsCount] = Item(overlay.itemsCount, _value);
}
}

当编译上面的代码，我得到错误:

TypeError: Uninitialized mapping. Mappings cannot be created dynamically, you have to assign them from a state variable.
--> TestC.sol:21:5:
|
21 |     mapping(uint => Item) memory items;
|     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

不确定如何处理这个错误。其次，需要确认在嵌套映射字典中添加新值的方法是否正确?

Answer 1

映射不能在函数内部声明，不能在memory状态下声明。该类型只有storage状态。也就是说，要将映射传递到结构中，可以设置嵌套映射的键并在其中传递相对结构。我试着像这样调整你的智能合约:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.4;
contract TestContract {
struct Item {
uint itemId;
uint itemValue;
}
struct OverlayingItemStruct {
mapping(uint => Item) items;
uint overlayingId;
uint itemsCount;
}
mapping(uint => OverlayingItemStruct) public overlayingItems;

uint public overlayCount;
function addOverlayingItemsStruct(uint _value) external {
overlayCount ++;
// NOTE: I declared a new Item struct
Item memory item = Item(1, _value);
// NOTE: I set into items mapping key value 1, Item struct created in row above this 
overlayingItems[overlayCount].items[1] = item;
}
function addItem(uint _value, uint _overlayId) external {
OverlayingItemStruct storage overlay = overlayingItems[_overlayId];
overlay.itemsCount ++;
overlay.items[overlay.itemsCount] = Item(overlay.itemsCount, _value);
}
}