I have a Map of a List. I am managing the data in the map and the list. I have it working for now, but wanted to find out if there is a better way to do this.

mapping (bytes32 => Receipts[]) receiptsByPersonMap;
Receipts[] dummyReceiptsList;

Receipts newReceipt = new Receipts(_person, _cost);

dummyReceiptsList = receiptsByPersonMap[_person];

receiptsByPersonMap[_person] = dummyReceiptsList;

This works for now. it seems that the last line is irrelevant - if receiptsList is pointing to the same storage space. Any suggestion of a better way to do this.

1 Answer 1


Why not do it in one go? Something like:

receiptsByPersonMap[_person].push(new Receipts(_person, _cost));

Incidentally, this may just be an artifact of the way you've simplified the question to post here, but since _person is the key of the mapping where you store your Receipts record, you can't access it unless you already know _person, so you should be able to remove _person from the struct. At that point the struct only contains one item, so you could get rid of it entirely and just store cost in a bytes32 => uint256[] mapping.

  • Thanks @EdmundEdgar. Your suggestion is perfect.. Yes, I had simplified the struct for this question.
    – userDSSR
    Commented Oct 4, 2017 at 14:16

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