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看到了一片文章，EOS多索引表的使用指南，感觉仍是挺好的，所以拿出来分享一下。

词汇表

code :是指已发布智能合约的account_name。

scope:account_name所触及数据规模。

table_name: 存储在内存中的表的称谓。

代码分化

要存储的结构

要在多索引表中存储的数据是limit_order结构。primary_key()，get_expiration()，get_price()函数用于回来表。回来的表将根据调用的函数排序。

struct limit_order {

uint64_t id;

uint128_t price;

uint64_t expiration;

account_name owner;

auto primary_key() const { return id; }

uint64_t get_expiration() const { return expiration; }

uint128_t get_price() const { return price; }

EOSLIB_SERIALIZE( limit_order, ( id )( price )( expiration )( owner ) )

};

建一个多索引表

auto payer = ilm.get_account();…

payer是保存帐户的变量，它将账单元素添加到多索引表中，并批改已经在多索引表中的元素。

…

eosio::multi_index< N( orders ), limit_order, …

N(orders)是多索引表的称谓，limit_order是要存储在表中的数据。

…

indexed_by< N( byexp ), const_mem_fun< limit_order, uint64_t,

&limit_order::get_expiration> >,…

indexed_by< N( byexp ), const_mem_fun< limit_order, uint64_t, &limit_order::get_expiration> >界说了多索引表的索引方法。N(byexp)是这个索引的称谓。const_mem_fun标明正在查询的数据类型、limit_order的变量的类型是uint64_t，将使用get_expiration函数获取变量。

…

indexed_by< N( byprice ), const_mem_fun< limit_order, uint128_t, &limit_order::get_price> >…

indexed_by< N( byprice ), const_mem_fun< limit_order, uint128_t, &limit_order::get_price> >界说了多索引表的索引方法。N(byprice)是这个索引的称谓。const_mem_fun标明正在查询的数据类型、limit_order的变量的类型是uint128_t，将使用get_price函数获取变量。

orders( N( limitorders ), N( limitorders )

orders即是多索引表。

auto payer = ilm.get_account();

print(“Creating multi index table ‘orders’.\n”);eosio::multi_index< N( orders ), limit_order,

indexed_by< N( byexp ), const_mem_fun< limit_order, uint64_t, &limit_order::get_expiration> >,

indexed_by< N( byprice ), const_mem_fun< limit_order, uint128_t, &limit_order::get_price> >

> orders( N( limitorders ), N( limitorders ) );

添加多索引表

下面，将两个limit_order添加到orders表中。请注意，payer是正在批改orders表的“账单”帐户。

orders.emplace( payer, [&]( auto& o ) {

o.id = 1;

o.expiration = 300;

o.owner = N(dan);

});

auto order2 = orders.emplace( payer, [&]( auto& o ) {

o.id = 2;

o.expiration = 200;

o.owner = N(thomas);

});

按照主键排序

默许的orders表按照主键排序。

print(“Items sorted by primary key:\n”);for( const auto& item : orders ) {

print(" ID=", item.id, “, expiration=”, item.expiration, “, owner=”, name{item.owner}, “\n”);

}

按第二索引expiration排序

orders表通过expiration进行排序并分配给expidx。

auto expidx = orders.get_index();

print(“Items sorted by expiration:\n”);for( const auto& item : expidx ) {

print(" ID=", item.id, “, expiration=”, item.expiration, “, owner=”, name{item.owner}, “\n”);

}

按第二索引price排序

orders表通过price进行排序并分配给oridx。

auto pridx = orders.get_index();

print(“Items sorted by price:\n”);for( const auto& item : pridx ) {

print(" ID=", item.id, “, expiration=”, item.expiration, “, owner=”, name{item.owner}, “\n”);

}

批改一个输入值

下面，“ID＝2”的条目被批改。请注意，payer是正在批改orders表的“账单”帐户。

print(“Modifying expiration of order with ID=2 to 400.\n”);

orders.modify( order2, payer, [&]( auto& o ) {

o.expiration = 400;

});

得到一个最小值

auto lower = expidx.lower_bound(100);

print(“First order with an expiration of at least 100 has ID=”, lower->id, " and expiration=", lower->get_expiration(), “\n”);

完好的.cpp文件

#include #include #include

using namespace eosio;

namespace limit_order_table {

struct limit_order {uint64_t     id;uint128_t    price;uint64_t     expiration;account_name owner;auto primary_key() const { return id; }uint64_t get_expiration() const { return expiration; }

uint128_t get_price() const { return price;

}

EOSLIB_SERIALIZE( limit_order, ( id )( price )( expiration )( owner ) )

};

class limit_order_table {

public:

ACTION( N( limitorders ), issue_limit_order ) {

EOSLIB_SERIALIZE( issue_limit_order )

    };

static void on( const issue_limit_order& ilm ) {

auto payer = ilm.get_account();

print(“Creating multi index table ‘orders’.\n”);

eosio::multi_index< N( orders ), limit_order,

indexed_by< N( byexp ), const_mem_fun< limit_order, uint64_t, &limit_order::get_expiration> >,

indexed_by< N( byprice ), const_mem_fun< limit_order, uint128_t, &limit_order::get_price> >

orders( N( limitorders ), N( limitorders ) );

        orders.emplace( payer, [&]( auto& o ) {o.id = 1;o.expiration = 300;o.owner = N(dan);});auto order2 = orders.emplace( payer, [&]( auto& o ) {o.id = 2;o.expiration = 200;o.owner = N(thomas);});print("Items sorted by primary key:\n");for( const auto& item : orders ) {print(" ID=", item.id, ", expiration=", item.expiration, ", owner=", name{item.owner}, "\n");}auto expidx = orders.get_index();print("Items sorted by expiration:\n");for( const auto& item : expidx ) {print(" ID=", item.id, ", expiration=", item.expiration, ", owner=", name{item.owner}, "\n");}auto pridx = orders.get_index();print("Items sorted by price:\n");for( const auto& item : pridx ) {print(" ID=", item.id, ", expiration=", item.expiration, ", owner=", name{item.owner}, "\n");}print("Modifying expiration of order with ID=2 to 400.\n");orders.modify( order2, payer, [&]( auto& o ) {o.expiration = 400;});auto lower = expidx.lower_bound(100);print("First order with an expiration of at least 100 has ID=", lower->id, " and expiration=", lower->get_expiration(), "\n");

};

} /// limit_order_table

namespace limit_order_table {

extern “C” {

of events to this contract

  void apply( uint64_t code, uint64_t action ) {require_auth( code );eosio_assert( eosio::dispatch< limit_order_table, limit_order_table::issue_limit_order >( code, action ), "Could not dispatch" );}

}

}

删去表

表不能直接删去，但是，在删去全部行之后，表将自动删去。