我想在 get 方法中使用 Promise 返回值。 Node.js 休息 API

发布于 2025-01-10 20:07:37 字数 690 浏览 0 评论 0原文

我正在创建一个休息 api。我的 get 方法将根据合约的总供应值返回结果，否则不会响应，但我对合约发出的请求返回一个承诺。我该如何使用这个值？

const NameContract = new web3.eth.Contract(abi, '0xE3A2beCa..........1D901F8');
NameContract.methods.totalSupply().call().then(value => console.log(value))


app.get('/:id', (req, res) => {
    let id = parseInt(req.params.id);
    //I want to use an if here. 
    //I want to throw the query according to the value returned from above,
    // but it returns a promise, how can I use it value?
    nft.findOne({ id: id }, (err, doc) => {
        if (doc != null) {
            res.json(doc)
        }
        else {
            res.status(404).json(err)
        }
    });

});

原文

I am creating a rest api. My get method will return the result according to the total supply value of the contract or it will not respond, but the request I made to the contract returns a promise. How can I use this value?

const NameContract = new web3.eth.Contract(abi, '0xE3A2beCa..........1D901F8');
NameContract.methods.totalSupply().call().then(value => console.log(value))


app.get('/:id', (req, res) => {
    let id = parseInt(req.params.id);
    //I want to use an if here. 
    //I want to throw the query according to the value returned from above,
    // but it returns a promise, how can I use it value?
    nft.findOne({ id: id }, (err, doc) => {
        if (doc != null) {
            res.json(doc)
        }
        else {
            res.status(404).json(err)
        }
    });

});

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热鲨 2025-01-17 20:07:37

尝试保存其值最终将成为总值的承诺

 const pTotalSupply = NameContract.methods.totalSupply().call();

（假设这是有效的 - .call 方法看起来有点奇怪）。然后，选项是

在满足上述 pTotalSupply 之前不启动服务器，提供总供应量是一个静态值，并且服务器必须处理一个名称合同，
等待在 app.get 处理程序中获取结果，方法是在异步函数体内使用 await 运算符，或者将请求处理包装在 Promise >then 参数函数，或
使用一个承诺 then 调用来保存供应值并在两部分 app.get 处理程序中调用 next。这更像是一种面向表达的解决方案，使用以下模式：

app.get('/:id', (req, res, next) => {
    pTotalSupply.then( value => {
        res.locals.value = value;
        next();
    }
    .catch( err => res.status(500).send("server error")); // or whatever
 }
 , (req, res) => {
    const value = res.locals.value;
    let id = parseInt(req.params.id);
    // process request with value and id:
    ...
 });

第二个选项包含在如何从异步调用返回响应

Try saving the promise whose value will end up being the total value

 const pTotalSupply = NameContract.methods.totalSupply().call();

(assuming this is valid - the .call method looks a little strange). Options then are to

Not start the server until pTotalSupply above has been fulfilled, provided total supply is a static value and there to be only one name contract the server has to deal with,
Wait for the result to be obtained within the app.get handler, either by using an await operator inside an asynchronous function body, or wrapping request processing in a promise then argument function, or
Using a promise then call to save the supply value and call next in a two part app.get handler. This is more an express oriented solution using a pattern along the lines of:

app.get('/:id', (req, res, next) => {
    pTotalSupply.then( value => {
        res.locals.value = value;
        next();
    }
    .catch( err => res.status(500).send("server error")); // or whatever
 }
 , (req, res) => {
    const value = res.locals.value;
    let id = parseInt(req.params.id);
    // process request with value and id:
    ...
 });

The second option is covered in answers to How to return the response from an asynchronous call

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