eosio::indexed_by

Module: Contracts API / Multi Index Table

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#include <multi_index.hpp>

Public Types

	Name
enum	constants { index_name = static_cast<uint64_t>(IndexName)}
typedef Extractor	secondary_extractor_type

Detailed Description

template <name::raw IndexName,
typename Extractor >
struct eosio::indexed_by;

Template Parameters:

• IndexName - is the name of the index. The name must be provided as an EOSIO base32 encoded 64-bit integer and must conform to the EOSIO naming requirements of a maximum of 13 characters, the first twelve from the lowercase characters a-z, digits 1-5, and ".", and if there is a 13th character, it is restricted to lowercase characters a-p and ".".
• Extractor - is a function call operator that takes a const reference to the table object type and returns either a secondary key type or a reference to a secondary key type. It is recommended to use the [eosio::const_mem_fun](/cdt/latest/reference/Classes/structeosio_1_1const__mem__fun) template, which is a type alias to the boost::multi_index::const_mem_fun. See the documentation for the Boost [const_mem_fun](/cdt/latest/reference/Classes/structeosio_1_1const__mem__fun) key extractor for more details.

The indexed_by struct is used to instantiate the indices for the Multi-Index table. In EOSIO, up to 16 secondary indices can be specified.

Example:

#include <eosiolib/eosio.hpp>
using namespace eosio;
class mycontract: eosio::contract {
  struct record {
     uint64_t    primary;
     uint128_t   secondary;
     uint64_t primary_key() const { return primary; }
     uint128_t get_secondary() const { return secondary; }
   };
  public:
    mycontract(name receiver, name code, datastream<const char*> ds):contract(receiver, code, ds){}
    void myaction() {
      auto code = _self;
      auto scope = _self;
      multi_index<"mytable"_n, record,
                 indexed_by< "bysecondary"_n, const_mem_fun<record, uint128_t, &record::get_secondary> > > table( code, scope);
    }
}
EOSIO_DISPATCH( mycontract, (myaction) )

Public Types Documentation

enum constants

Enumerator	Value	Description
index_name	static_cast<uint64_t>(IndexName)

typedef secondary_extractor_type

typedef Extractor eosio::indexed_by< IndexName, Extractor >::secondary_extractor_type;

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Updated on 2022-12-05 at 15:38:07 +0000