How to check if bytes variable is empty?

Question

I have a mapping in my smart contract with bytes32 keys and bytes values. How can I check if bytes value exists for specific key? Mapping is something like this:

mapping(bytes32 => bytes) public Countries;

Answer 1

You can check it via .length. It will be 0 if it is empty/uninitialised.

Countries[key].length

Answer 2

This solution stands for bytes32:

Countries[_user] == "" // Returns true if `Countries[_user]` is not initialized

---

pragma solidity ^0.6.0;

mapping(address => bytes32) public Countries;   

function isCountriesInitialized(address _user) external view returns (bool) 
{
    if (Countries[_user] == "")
        return false;

    return true;
}

---

I observe that on solidity v0.6.0 it may return 32 for length even though it is not mapped.

Example of its returned value:

b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'