I want to access last N documents from google firestore collection. The key for documents are timestamp in ISO format. The collection first needs to be sorted on timestamp keys and the last N documents updated are to be retrieved. This operation has to be realtime and fast.
events(collection) =>
documents as below:
2019-01-07T08:21:18.600Z => {
symbolname: '10900CE',
price: '10825.0',
timestamp: '2019-01-07T13:51:18Z',
quantity: '2.0',
side: 'SELL' }
2019-01-07T08:21:28.614Z => {
symbolname: '10800PE',
price: '10825.0',
timestamp: '2019-01-07T13:51:28Z',
quantity: '2.0',
side: 'BUY' }
2019-01-07T09:45:24.783Z => { side: 'SELL',
symbolname: '10800PE',
price: '10805.0',
timestamp: '2019-01-07T15:15:24Z',
quantity: '2.0' }
I currently loop through the collection and add the keys to an array and then sort the array and get last N document by those keys as following:
var ids = []
db.collection('events').get()
.then((snapshot) => {
snapshot.forEach((doc) => {
ids.push(doc.id)
});
})
.then(()=>{
//sortIds(ids);
console.log(JSON.stringify(ids[ids.length-2])) //second last entry 2019-01-07T08:21:28.614Z
})
.catch((err) => {
console.log('Error getting documents', err);
});
This operation takes a long time if collection size increases. Is there an optimal way of achieving this (sorting/orderBy-descending collection and fetch last N documents)?
Thanks
也许是这样的:
db.collection('events').orderBy("timestamp").limit(n)
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.