Adding unique address to each item
https://medium.com/upstate-interactive/creating-a-contract-with-a-smart-contract-bdb67c5c8595
We want each item that was created to have its own unique address, to which customers can make payment.
I initially thought:
struct Item {
string id;
uint price;
itemState state;
address _payto;
}
However, this is would not work. How do we define/pre-allocate an address automatically to each item on creation? We do not control address creation and allocation on the EVM.
Solution
To get a unique address per item -> each item has its own smart contract. Therefore, the create() should result in deployment on a new item AND its smart contract.
We will split the code up, keeping the item smart contract as a separate child contract.
//SPDX-License-Identifier: MIT
pragma solidity ^0.8.1;
import "./ItemManager.sol";
contract Item {
uint public priceInWei;
uint public paidWei;
uint public index;
//variable of type ItemManager -> contract object.
ItemManager parentContract;
// creation requires inputs: price & index.
constructor(ItemManager _parentContract, uint _priceInWei, uint _index) public {
priceInWei = _priceInWei;
index = _index;
parentContract = _parentContract;
}
receive() external payable {
require(msg.value == priceInWei, "We don't support partial payments");
require(paidWei == 0, "Item is already paid!");
paidWei += msg.value;
(bool success, ) = address(parentContract).call{value:msg.value}(abi.encodeWithSignature("triggerPayment(uint256)", index));
require(success, "Delivery did not work");
}
fallback () external {
}
}
How do these 2 contracts interact?
createItem
When createItem() is called Item item = new Item(this, _price, item_index)
, creates a new instance of the Item contract based on the price provided and index counter.
this
: the current contract, explicitly convertible to address.
this
is passed into the child contract's constructor (Item{}
), for the field ItemManager _parentContract
, where it eventually assigned to variable parentContract
parentContract = _parentContract;
// evaluates to:
parentContract = this;
This is to store the parent contract association.
struc Item {}
struc Item now has Item _item
; which is a contract object. It is assigned value under the createItem(), after the new item contract object has been created.
item_list[item_index]._item = item;
Thoughts
Thoughts
This approach allows us to create an item using the parent contract, assign values to both parent and child
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