多索引表 创建多索引表

Posted 2021-10-28 thefist11

1. 创建表

• class/struct 定义一个持久化对象。
• 该对象需要有一个const的成员作为主键，类型为uint64_t
• 二级主键可选，提供不同的键类型
• 为每个二级索引定义一个键导出器，键导出器是一个函数，可以用来从Multi_index表中获取键

multi_index_example.hpp

#include <eosio/eosio.hpp>
using namespace eosio;

// multi index example contract class
class [[eosio::contract]] multi_index_example : public contract {
   public:
      using contract::contract;

      // contract class constructor
      multi_index_example( name receiver, name code, datastream<const char*> ds ) :
         // contract base class contructor
         contract(receiver, code, ds),
         // instantiate multi index instance as data member (find it defined below)
         testtab(receiver, receiver.value)
         { }

      // the row structure of the multi index table, that is, each row of the table
      // will contain an instance of this type of structure
      struct [[eosio::table]] test_table {
        // this field stores a name for each row of the multi index table
        name test_primary;
        // additional data stored in table row
        uint64_t datum;
        // mandatory definition for primary key getter
        uint64_t primary_key( ) const { return test_primary.value; }
      };

      // the multi index type definition, for ease of use define a type alias `test_tables`, 
      // based on the multi_index template type, parametarized with a random name and 
      // the test_table data structure
      typedef eosio::multi_index<"testtaba"_n, test_table> test_tables;

      // the multi index table instance declared as a data member of type test_tables
      test_tables testtab;

      [[eosio::action]] void set( name user );
      [[eosio::action]] void print( name user );

      using set_action = action_wrapper<"set"_n, &multi_index_example::set>;
      using print_action = action_wrapper<"print"_n, &multi_index_example::print>;
};