How can I delete an element from a nested mapping - solidity

Question

I have a nested mapping that goes from address to planId to struct(subscription)
mapping(address => mapping(uint => subscription)) public subscriptions
I have a function to cancel a specific plan that has been created but when I trigger the function I got an error that says
The transaction ran out of gas. Please increase the Gas Limit.
When I debugged the error the debugger points the error inside the cancel function at the code line below
function cancel(uint planId) external {
Subscription storage subscription = subscriptions[msg.sender][planId];
require(
subscription.subscriber != address(0),
'this subscription does not exist'
);
delete subscriptions[msg.sender][planId]; // this one
emit SubscriptionCancelled(msg.sender, planId, block.timestamp);
}
How can I fix that error?
Thanks

Answer 1

I am facing a similar problem. Here's what I did, I realized that it's not possible to assign a default value to a nested mapping once you change it.
In your example, you can try assigning a struct with different values(which you can consider as a replacement for default) and then it wont throw error.
Following is my example:
// SPDX-License-Identifier: GPL-3.0
pragma solidity ^0.8.0;
contract test{
mapping(address=> mapping(uint => uint)) public address_id_liked;
function register(uint id) external{
address_id_liked[msg.sender][id] = 1;
}
function test_(uint index) external view returns(uint) {
uint out = address_id_liked[msg.sender][index];
return(out);
}
function ops(uint id, uint num) external {
address_id_liked[msg.sender][id] = num;
}
}
In the ops function, I wanted my mapping to have a default value but it's not happening. So I tried inputting the value which I want to assign to nested mapping. And it's taking all uint values except 0(the default)
P.S- I was using mapping(address=> mapping(uint => bool)) public address_id_liked previously. But I am unable to delete/assign false, hence I tried with uint.
Hope this helps!