从数据库中获取实时数据

Question

我有一份 solidity 的代币合约。我想制作映射 isWhitelisted[msg.sender]，我想我应该使用

为此。当个人钱包在 sql 数据库 上列出时，isWhitelisted return 怎么可能只有？

Answer 1

据我所知你不能这样检查。（到目前为止）

但我自己使用的解决方法是将映射与结构一起使用。

struct testStruct {
    string test;
    bool isValue;
}

mapping (address => testStruct ) public tests;

// Than you can do

function isWhitelisted() public view returns (bool isValue_)
{
    if (tests[msg.sender].isValue) {
        uniName_ = tests[msg.sender].isValue;
    }
}


// or use it like this

require(tests[msg.sender].isValue);

bool isValue 仅在检查 msg.sender 是否在映射中可用时才需要。如果您提供更多关于您到目前为止所做的事情的信息，我可以更好地帮助您。

更新

示例：http://dapps.oraclize.it/browser-solidity/#gist=9817193e5b05206847ed1fcd1d16bd1d&version=soljson-v0.4.21+commit.dfe3193c.js

DieselPrice.sol，简单XML API端点：https://www.fueleconomy.gov/ws/rest/fuelprices

function __callback(bytes32 myid, string result) {
    if (msg.sender != oraclize_cbAddress()) throw;
    newDieselPrice(result);
    DieselPriceUSD = parseInt(result, 2); // let's save it as $ cents
    // do something with the USD Diesel price
}

function update() payable {
    newOraclizeQuery("Oraclize query was sent, standing by for the answer..");
    oraclize_query("URL", "xml(https://www.fueleconomy.gov/ws/rest/fuelprices).fuelPrices.diesel");
}

在 __callback 中，XML 元素 "fuelPrices.diesel" 将保存到 public DieselPriceUSD 变量中。新示例：

function __callback(bytes32 myid, bool isWhitelisted ) { // I dont know if type casting is possible this way
    if (msg.sender != oraclize_cbAddress()) throw;
    if (isWhitelisted) {
       callEventXYZ();
    }

}


function checkWhitelist() payable {
    newOraclizeQuery("Oraclize query was sent, standing by for the answer..");
    oraclize_query("URL", "xml(https://YourXMLAPIEndpoint?msgaddress=" + msg.sender +").isWhitelisted.value"); // Or something similar to this
}

要将 msg.sender 地址连接到查询 url 中，您可以查看此 link： http://docs.oraclize.it/#ethereum-quick-start

例子： strConcat()

// Absolute time: get the result from the given datasource at the specified UTC timestamp in the future
oraclize_query(scheduled_arrivaltime+3*3600,
  "WolframAlpha", strConcat("flight ", flight_number, " landed"));

OR Post msg.sender 作为 JSON 到 API:

// The URL datasource also supports a supplement argument, useful for creating HTTP POST requests.
// If that argument is a valid JSON string, it will be automatically sent as JSON.
oraclize_query("URL", "json(https://shapeshift.io/sendamount).success.deposit",
  '{"pair":"eth_btc","amount":"1","withdrawal":"1AAcCo21EUc1jbocjssSQDzLna9Vem2UN5"}')

从数据库中获取实时数据

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