[英]Javascript - Collect data from mongodb from multiple collections then merge into array
I want to fetch the newest object from multiple collections and save all into an array with collection name as key and the newest object as value. 我想从多个集合中获取最新对象,然后将所有对象保存到一个数组中,集合名称为键,最新对象为值。
How can I achieve this sequentially or async? 我怎样才能顺序地或异步地做到这一点?
let dat = ["test", "test2"];
let merged = [];
dat.map((collName) => {
const promise = new Promise((resolve, reject) => {
db.collection(collName).find().sort({ timestamp: -1 }).limit(1).forEach((d) => {
resolve(d);
});
})
.then((result) => {
merged.push(result);
});
console.log(merged);
The log at the end gives me an empty array. 最后的日志给了我一个空数组。
Looks like an async issue to me. 对我来说似乎是一个异步问题。 You can wrap your code in a function and return the promise chain all the way down.
您可以将代码包装在一个函数中,并一直返回承诺链。 This should give you the full array.
这应该给您完整的阵列。 Then use it as you need.
然后根据需要使用它。
let dat = ["test", "test2"] const mergeData = async () => { const promises = await dat.map(async (collName) => { let value = '' await new Promise((resolve, reject) => { db.collection(collName).find().sort({ timestamp: -1 }).limit(1).forEach((d) => { resolve(d) }) }).then(response => { value = response }) return value }) const results = await Promise.all(promises) console.log('results: ', results) } mergeData()
You could try using async/await as: 您可以尝试使用async / await作为:
let dat = ["test", "test2"];
const promises = dat.map(async (collName) => {
try {
const data = await db.collection(collName)
.find({})
.sort({ timestamp: -1 })
.limit(1)
.toArray();
return data[0];
} catch(err) {
console.error(err);
}
});
(async () => {
const merged = await Promise.all(promises);
console.log(merged);
})();
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