<pre><code class=”hljs sql”>

vector<asset> read_only::get_currency_balance( const read_only::get_currency_balance_params& p )const {

//调用指定数据表操作接口，表拥有者为p.code
const abi_def abi = eosio::chain_apis::get_abi( db, p.code );

//按账户名返回表信息
auto table_type = get_table_type( abi, “accounts” );

//声明一个vector用以保存返回结果
vector<asset> results;
//调用walk_key_value_table模板，用以检索数据

walk_key_value_table(p.code, p.account, N(accounts), [&](const key_value_object& obj){

//判断表中数据合规性
EOS_ASSERT( obj.value.size() >= sizeof(asset), chain::asset_type_exception, “Invalid data on table”);
//声明cursor资产，用作迭代结果返回值

asset cursor;
//初始化待检索数据

fc::datastream<const char *> ds(obj.value.data(), obj.value.size());

fc::raw::unpack(ds, cursor);

</code></pre>

EOS_ASSERT( cursor.get_symbol().valid(), chain::asset_type_exception, “Invalid asset”);
//判断返回结果是否为指定类型代币，若是则压入results中

if( !p.symbol || boost::iequals(cursor.symbol_name(), *p.symbol) ) {

results.emplace_back(cursor);

}

return !(p.symbol && boost::iequals(cursor.symbol_name(), *p.symbol));

});

return results;

}

1.2 get_currency_stats函数

该函数的功能用于返回某种代币的发行状态信息，具体执行逻辑如下：

fc::variant read_only::get_currency_stats( const read_only::get_currency_stats_params& p )const {

fc::mutable_variant_object results;

//调用指定数据表操作接口，表拥有者为p.code

const abi_def abi = eosio::chain_apis::get_abi( db, p.code );

auto table_type = get_table_type( abi, “stat” );
//设置检索范围为表全局

uint64_t scope = ( eosio::chain::string_to_symbol( 0, boost::algorithm::to_upper_copy(p.symbol).c_str() ) >> 8 );
//重复上述流程

walk_key_value_table(p.code, scope, N(stat), [&](const key_value_object& obj){

EOS_ASSERT( obj.value.size() >= sizeof(read_only::get_currency_stats_result), chain::asset_type_exception, “Invalid data on table”);

fc::datastream<const char *> ds(obj.value.data(), obj.value.size());

read_only::get_currency_stats_result result;

fc::raw::unpack(ds, result.supply);

fc::raw::unpack(ds, result.max_supply);

fc::raw::unpack(ds, result.issuer);

results[result.supply.symbol_name()] = result;

return true;

});

return results;

}

1.3 get_producers函数

该函数用于返回当前出块节点信息，具体执行逻辑如下：

read_only::get_producers_result read_only::get_producers( const read_only::get_producers_params& p ) const {

//获取EOSIO账户下的智能合约中拥有的数据表接口

const abi_def abi = eosio::chain_apis::get_abi(db, N(eosio));

const auto table_type = get_table_type(abi, N(producers));

const abi_serializer abis{ abi, abi_serializer_max_time };

//判断返回结果数据类型是否合规

EOS_ASSERT(table_type == KEYi64, chain::contract_table_query_exception, “Invalid table type ${type} for table producers”, (“type”,table_type));

//设置数据表指针

const auto& d = db.db();

const auto lower = name{p.lower_bound};

static const uint8_t secondary_index_num = 0;

//查找并返回保存producers数据的数据表指针

const auto* const table_id = d.find<chain::table_id_object, chain::by_code_scope_table>(boost::make_tuple(N(eosio), N(eosio), N(producers)));

const auto* const secondary_table_id = d.find<chain::table_id_object, chain::by_code_scope_table>(boost::make_tuple(N(eosio), N(eosio), N(producers) | secondary_index_num));

EOS_ASSERT(table_id && secondary_table_id, chain::contract_table_query_exception, “Missing producers table”);

//初始化查找指针

const auto& kv_index = d.get_index<key_value_index, by_scope_primary>();

const auto& secondary_index = d.get_index<index_double_index>().indices();

const auto& secondary_index_by_primary = secondary_index.get<by_primary>();

const auto& secondary_index_by_secondary = secondary_index.get<by_secondary>();

//声明get_producers_result类对象，用于存储返回值

read_only::get_producers_result result;

const auto stopTime = fc::time_point::now() + fc::microseconds(1000 * 10); // 10ms

vector<char> data;

//声明一个匿名函数，调用lower_bound检索方法

auto it = [&]{

if(lower.value == 0)

return secondary_index_by_secondary.lower_bound(

boost::make_tuple(secondary_table_id->id, to_softfloat64(std::numeric_limits<double>::lowest()), 0));

else

return secondary_index.project<by_secondary>(

secondary_index_by_primary.lower_bound(

boost::make_tuple(secondary_table_id->id, lower.value)));

}();

//逐个压入检索结果

for( ; it != secondary_index_by_secondary.end() && it->t_id == secondary_table_id->id; ++it ) {

if (result.rows.size() >= p.limit || fc::time_point::now() > stopTime) {

result.more = name{it->primary_key}.to_string();

break;

}

copy_inline_row(*kv_index.find(boost::make_tuple(table_id->id, it->primary_key)), data);

if (p.json)

result.rows.emplace_back(abis.binary_to_variant(abis.get_table_type(N(producers)), data, abi_serializer_max_time));

else

result.rows.emplace_back(fc::variant(data));

}

//最后压入总投票权重值

result.total_producer_vote_weight = get_global_row(d, abi, abis, abi_serializer_max_time)[“total_producer_vote_weight”].as_double();

return result;

}