testmeta.cpp

#include <eosio/eosio.hpp>

using namespace eosio;

class [[eosio::contract]] testmeta : public contract {
  public:
    using contract::contract;

    [[eosio::action]]
    void hi( name user ) {
        print( "Hello, ", user);
    }

    TABLE meta { 
        name key; 
        std::string value; 
        uint64_t primary_key() const { return key.value; } 
    }; 
    typedef eosio::multi_index<"meta"_n, meta> _t_meta; 
    [[eosio::action]] 
    void setmeta(
        name key, 
        std::string value 
    ){ 
        require_auth(_self); 
        _t_meta items( _self, _self.value ); 
        auto existing = items.find( key.value ); 
        if(existing == items.end()) { 
            items.emplace(_self, [&]( auto& a ){ 
                a.key = key; 
                a.value = value; 
            }); 
        } else { 
            items.modify( *existing, eosio::same_payer, [&]( auto& a ) { 
                a.value = value; 
            }); 
        } 
    }       
};