[英]What is the best way to approach pagination with Promises?
我和我的朋友正在履行諾言,並且我們確保在返回到初始調用之前獲取所有數據頁。 有沒有更簡單的方法來解決這個問題?
function getDocuments(startIndex, result, entries) {
startIndex = typeof startIndex !== 'undefined' ? startIndex : 0;
result = typeof result !== 'undefined' ? result : {};
entries = typeof entries !== 'undefined' ? entries : [];
// build our entries set with the result parameter
for(var i in result.items) {
try
{
var id = result.items[i].id;
var name = result.items[i].name;
var content = result.items[i].content;
var entry = { "id": id, "name": name, "content": content };
entries.push(entry);
}
catch(e) {
}
}
// return a promise that fulfills a promise that then returns either a promise or a result.
return new Promise(function(fulfill, reject) {
// fulfill the promise and resolve the value, we pass a recursive promise as the value.
fulfill(documentClient.getDocuments({ "startIndex": startIndex }).then(function(result) { // once our request is made, let's check the page count.
var startIndex = result.startIndex;
var pageSize = result.pageSize;
var totalCount = result.totalCount;
if (startIndex + pageSize <= totalCount) { // if our current position is not at the end of the pages, return a promise with our current data and our current entries.
return getDocuments(startIndex + pageSize, result, entries);
}
return entries; // otherwise our entries will bubble back up the stack and be resolved into the initial fulfill value.
}));
});
}
getDocuments().then(function(d) { console.log(d.length); });
我的調整:
function getDocuments(startIndex, result, entries) {
startIndex = typeof startIndex !== 'undefined' ? startIndex : 0;
result = typeof result !== 'undefined' ? result : {};
entries = typeof entries !== 'undefined' ? entries : [];
// build our entries set with the result parameter
// ...
// return a promise that fulfills a promise that then returns either a promise or a result.
return documentClient.getDocuments({ "startIndex": startIndex }).then(function(result) { // once our request is made, let's check the page count.
var startIndex = result.startIndex;
var pageSize = result.pageSize;
var totalCount = result.totalCount;
if (startIndex + pageSize <= totalCount) { // if our current position is not at the end of the pages, return a promise with our current data and our current entries.
return getDocuments(startIndex + pageSize, result, entries);
}
return entries; // otherwise our entries will bubble back up the stack and be resolved into the initial fulfill value.
});
}
getDocuments().then(function(d) { console.log(d.length); });
是的,您可以像這樣將諾言鏈接起來,因為documentClient.getDocuments
返回諾言。
function getDocuments(startIndex, result, entries) {
// ...
return documentClient.getDocuments({ "startIndex": startIndex }).then(function(result) {
// ...
return entries; // otherwise our entries will bubble back up the stack and be resolved into the initial fulfill value.
});
}
getDocuments().then(function(d) { console.log(d.length); });
在getDocuments
有一個代碼路徑,該路徑不會以新的承諾結尾
這是一個簡單的例子
function defer(fn) {
setTimeout(fn, 100);
}
function promiseChain(i, msg) {
if (i <= 0) return msg; // end code path
return new Promise((res, rej) => {
defer(e => res(promiseChain(i - 1, msg)));
});
}
promiseChain(10, "Hello World!").then(data => console.log(data));
// "Hello World!" logged after ten 100ms timeouts
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