struct [[ eosio::table, eosio::contract("voting") ]] identity
{
    uint64_t key;
    key256 identityHash;
    time_point_sec createdAt;

    uint64_t primary_key() const { return key; }
    key256 by_hash() const { return identityHash; }
};
typedef multi_index<"identity"_n, identity,
    indexed_by< "by_hash"_n, const_mem_fun<identity, key256, &identity::by_hash> >
> identity_index;

voting::identity_index identities(_code, _code.value);
auto itr = identities.find(out);
eosio_assert(itr == identities.end(), "User already registered to vote!");

std::vector<uint64_t> keysForDeletionFromVotes;
    // find items which are for the named poll
    for(auto& item : _votes) {
        if (item.pollName == pollName) {
            keysForDeletionFromVotes.push_back(item.key);
        }
    }