Questions related to Multi-Indexes for Smart Contracts Tables

The EOSIO Multi-Index API provides a C++ interface to the EOSIO database. The EOSIO Multi-Index API is patterned after Boost Multi-Index Containers. This API provides a model for object storage with rich retrieval capabilities, enabling the use of multiple indices with different sorting and access semantics. The Multi-Index API is provided by the eosio::multi_index C++ class found in the contracts/eosiolib folder of the EOSIO/eos GitHub repository. This class enables a contract written in C++ to read and modify persistent state in the EOSIO database.