EOS之记事本智能合约

Posted 2020-11-17 tokenpai

EOS记事本智能合约

本次分享的内容是一个记事本合约，调用合约中的写入动作可以将文本和作者保存到数据库中，通过记事本合约来学习EOS智能合约数据存储当中的主键自增。

合约动作

• 写入动作

记事本合约必须要有的写入文本action，用来存储记录文本和记录作者。

• 删除动作

记事本中同样需要有删除记录的action，用来删除记录信息。

合约代码

note.cpp

#include <eosiolib/eosio.hpp>
#include <string>

using namespace eosio;

using std::string;

class record : public eosio::contract {
public:
    /// @abi table notes i64
    struct note {
        uint64_t        id;
        account_name    author;
        string          text;

        auto primary_key() const { return id; }

    };

    typedef multi_index<N(notes), note> notes;

    using contract::contract;

    /// @abi action
    void write(account_name author, string text) {

        require_auth(author);

        print("Hello, ", name{author});

        notes nt( _self, _self );

        uint64_t noteId;

        nt.emplace(author, [&](auto &n) {
            n.id = nt.available_primary_key();// 主键自增
            n.author = author;
            n.text = text;
            noteId = n.id;
        });

        print("----noteId = ", noteId);
    }

    void remove(uint64_t id) {

        notes nt( _self, _self );
        auto it = nt.find( id );
        eosio_assert( it != nt.end(), "the id not found" );
        require_auth(it->author);
        nt.erase( it );
    }

};

EOSIO_ABI(record, (write)(remove))

合约涉及数据库操作部分

• 在表中增加记录：emplace
• 删除一条数据：erase
• 查询记录：find
• 主键自增：available_primary_key

其中主键自增非常重要，不写主键自增会导致无法存入多条记录。

合约调用演示

• 调用write动作

$ cleos push action note write ‘{"author":"user","text":"This is my first diary"}‘ -p user
executed transaction: ab59fc4e04342690af46d5bf4dd48c8418d4655e8bcaea81ca3fdc0c99b6fed7  216 bytes  511 us
#          note <= note::write                  {"author":"user","text":"This is my first diary"}
>> Hello, user----noteId = 0
warning: transaction executed locally, but may not be confirmed by the network yet

调用成功会返回信息，其中noteId是记录的id，在删除记录的时候需要用到。

• cleos get table 查询表

$ cleos get table note note notes
{
  "rows": [{
      "id": 0,
      "author": "user",
      "text": "This is my first diary"
    },{
      "id": 1,
      "author": "student",
      "text": "my name is student!"
    },{
      "id": 2,
      "author": "miaomiao",
      "text": "my name is miaomiao"
    }
  ],
  "more": false
}

• 调用remove动作

删除时进行了授权限制，每个账户只能删除自己的记录，无法删除其他账户的记录

错误的授权：

$ cleos push action note remove ‘{"id":2}‘ -p user
Error 3090004: missing required authority
Ensure that you have the related authority inside your transaction!;
If you are currently using ‘cleos push action‘ command, try to add the relevant authority using -p option.
Error Details:
missing authority of miaomiao

正确的授权：

$ cleos push action note remove ‘{"id":2}‘ -p miaomiao
executed transaction: 51eb63f0fdb7d5d01676e898a0f9bc144ee1feda344780042782f359541a578d  192 bytes  442 us
#          note <= note::remove                 {"id":2}

$ cleos get table note note notes
{
  "rows": [{
      "id": 0,
      "author": "user",
      "text": "This is my first diary"
    },{
      "id": 1,
      "author": "student",
      "text": "my name is student!"
    }
  ],
  "more": false
}

在编写记事本合约时为了找到让主键增加的方法差了很多资料，也走了很多弯路。最后发现其实就是一行代码就能解决的事情。主键自增的使用详见这里。