[英]Recursion with promises on async calls
I am using an external api that I use as my datasource. 我正在使用用作数据源的外部api。 That api gives its data back based on a pagination like type.
该api根据类似分页的类型提供其数据。
So I can get data for page 1, 2, 3 etc. But the problem that I have is that I need all data at once, the api doesn't support this so I write it myself. 因此,我可以获取第1、2、3等页的数据。但是我遇到的问题是,我需要一次获取所有数据,api不支持此数据,所以我自己编写。
I have made the actual call code: 我已经做了实际的呼叫代码:
function getTransactionPart(start){
return new Promise(function(resolve, reject) {
const options = {
url: 'myurl?limit=40&start='+start,
json: true
};
let result = {total_transactions : 0, transactions : []};
request(options, function (error, response, body) {
if (error) {
return reject(result);
}
body.data.forEach(function (transaction) {
result.transactions.push({
timestamp: transaction.timestamp,
amount: transaction.amount,
confirmed: transaction.confirmed
});
});
result.total_transactions = body.total
return resolve(result);
})
})
}
The above code returns me the expected results with the limit that I gave. 上面的代码以给定的限制向我返回了预期的结果。 Also I get a number back (result.total_transactions) when this is more than 40 I need to make another call with 40 as start etc etc.
当这个大于40时,我也会得到一个数字(result.total_transactions),我需要用40作为开始等进行另一个呼叫,等等。
The code where I need to combine it: 我需要将其组合的代码:
function getTransactions(start) {
return new Promise(function(resolve, reject) {
getTransactionPart(start).then(result => {
if(result.total_transactions > 40) {
//next call
} else {
// return all?
}
console.log(result)
}).catch(error => {
console.error(error);
return r.json({
})
});
})
}
So I do the first call with getTransactionPart(0) after that the method itself needs to combine the result form all the sub calls and return the whole result as expected. 因此,我首先使用getTransactionPart(0)进行了调用,之后该方法本身需要将所有子调用的结果组合在一起,并按预期返回整个结果。 How can I do this with recursion and promises?
我该如何使用递归和承诺?
This is easier if you use an async
function and await
the request: 如果您使用
async
函数并await
请求,这会更容易:
async function getTransactions(start) {
const result = [];
for(let pos = start; ; pos += 40) {
const { total_transactions, transactions } = await getTransactionPart(pos);
result.push(...transactions);
if(total_transactions < 40) break;
}
return result;
}
For sure you could also do this recursively, but do you really need that? 当然,您也可以递归执行此操作,但是您真的需要吗?
async function getTransactions(start) {
const { total_transactions, transactions } = await getTransactionPart(pos);
if(total_transactions < 40)
return transactions;
return transactions.concat(await getTransactions(start + 40));
}
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