Solidity Mapping – How to Delete or Remove a Key from Mapping

mappingsolidity

I have the following map:

mapping (string => Category) categoryMap;

Let's say the key was mistyped, so I want to remove the key and add a correct one, how would I do that?

Function would be

  function updateCategoryLabel(string _newCategoryLabel, string _oldCategoryLabel) {
    categoryMap[_oldCategoryLabel].label = _newCategoryLabel;
    Category tmpCategory = categoryMap[_oldCategoryLabel];
    // Delete Key
    // create new key from _newCategoryLabel
      }

Thanks

Edit:

Here is what I was doing:

  function updateCategoryLabel(string _newCategoryLabel, string _oldCategoryLabel) {
    categoryMap[_oldCategoryLabel].label = _newCategoryLabel;
    Category tmpCategory = categoryMap[_oldCategoryLabel];
    delete categoryMap[_oldCategoryLabel];
    categoryMap[_newCategoryLabel] = tmpCategory;
  }

Category struct

  struct Category {
    string label;
    uint percent;
    address[] userList;
  }

Best Answer

Try this:

function updateCategoryLabel(string _newCategoryLabel, string _oldCategoryLabel) {
    categoryMap[_newCategoryLabel] = categoryMap[_oldCategoryLabel];
    delete categoryMap[_oldCategoryLabel];
}

Related Solutions

Solidity Memory Management – Does ‘Delete’ Free Mapping Space

Based on my Debug observation:

I have tested that:

Firstly I insert data into my map data-structure as I explained in my question.
Secondly, I have returned the address of first mapped index, which is 0, this could be done for other indexes as well (0:10).
Without a delete operation I can retrieve the data perfectly fine from the address of mapped Foo[]. But if I did the delete operation, Solidity gives an error.

This debug result: leads me to conclude that memory is freed or address does not contain any valid information.

Test code:

set_txn_hash     = my_contract.transact().map_insert();
contract_address = unmigrated_chain.wait.for_receipt(set_txn_hash)

for x in range(0, 9):
   for y in range(0, 9):
         output           = my_contract.call().get_(x, y);
         print(output);  //returns correct value.

set_txn_hash     = my_contract.transact().map_remove_map();                                             
contract_address = unmigrated_chain.wait.for_receipt(set_txn_hash)                                      

set_txn_hash     = my_contract.transact().get_map_address(0);
contract_address = unmigrated_chain.wait.for_receipt(set_txn_hash)

output           = my_contract.call().get_map();
print(output);

output           = my_contract.call().try_();
print(output);  //Solidity gives error if delete map_remove_map() is called

Additional functions inside my Contract:

  function map_insert(){
    for(uint i = 0; i < 10; i++)
      for(uint j = 0; j < 10; j++)
        add(i, i*10 + j);
  }

  function map_remove_map(){
    for(uint i = 0; i < 10; i++)
      delete_(i);
  }

  function map_remove_map_item(){
    for(uint i = 0; i < 10; i++)
      for(uint j = 0; j < 10; j++)
        delete_items(i, j);
  }

  function get_map_address(uint id) {
    uint addr;
    Foo[] a = foo[id];

    assembly{
    addr := a
        }
    map_address = addr;
  }

  function get_map() constant returns (uint){
    return map_address;
  }

  function try_() constant returns (uint ){
    uint addr = map_address;
    Foo[] a;
    assembly{
    a := addr
        }
    return a[1].x;  
  }

[Ethereum] Solidity function that accepts mapping as input

You can't pass the whole mapping. You could pass a struct internally. Ideally, you would enumerate the fields you really need to pass so you can create an interface that works with other contracts and clients.

Your example above, seems to pass a single member of the source mapping. I would interpret that roughly like this:

pragma solidity ^0.4.6;

contract testInputArray {

    mapping (string => string) aMapping;

    // Log event to print the message details
    event Log(address from, address to, string message);

    function sendMessage(address to, string key) {
        Log(msg.sender, to, aMapping[key]);
    }
}

Hope it helps.

P.S. It would be remiss to omit the usual preference for bytes32 over string if that's possible in this case. Left it as string for clarity.

Best Answer

Related Solutions

Solidity Memory Management – Does ‘Delete’ Free Mapping Space

[Ethereum] Solidity function that accepts mapping as input

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