Unable to make use of secondary index in multi-index table

Question

I am trying to add secondary index to my table so I can use it to query for elements based on it. My struct looks like this:

struct [[eosio::table]] user
  {
    name userAccount;         // user accountname - primary key
    std::string userKey;      // user random unique key
    std::string userName;     // user firstname
    std::string userLastname; // user lastname
    std::string userEmail;    // user email
    std::string userCity;     // user city
    std::string userMobile;   // user mobilephone
    std::string userCartype;  // user cartype
    uint64_t primary_key() const { return userAccount.value; }
    std::string secondary_key() const { return userEmail; }
  };

typedef multi_index<name("users"), user> users_table;.

So, the thing is, after I compile the contract and apply it to my account it says that there are no changes to the contract. Am I missing something ? Is there another way of getting user based on userEmail?

p.s The main purpouse of this is to use rpc.get_table_rows in order to retrieve the user info based on the userEmail.

Answer 1

You can't use a string as key type.

A secondary index supports several key types, listed below.

uint64_t           - Primitive 64-bit unsigned integer key
uint128_t          - Primitive 128-bit unsigned integer key, or a 128-bit fixed-size lexicographical key
checksum256        - 256-bit fixed-size lexicographical key
double             - Double precision floating point key
long double        - Quadruple precision floating point key