I'm trying to query Firebase database to get data ordered by timestamp.
我正在尝试查询Firebase数据库以获取按时间戳排序的数据。
1: This works but the data returned is not ordered by timestamp:
1：这有效，但返回的数据不按时间戳排序：
router.get('/articles', function(req, res, next) {
admin.database().ref('articles').orderByChild('timestamp').once('value').then(function (snapshot) {
let articles = snapshot.val();
console.log(articles);
res.render('articles', articles);
});
});
2: This returns me the data ordered by timestamp like I want (I can see it in the console.log), but I get this error:
2：这会返回我想要的按时间戳排序的数据（我可以在console.log中看到它），但是我收到此错误：
// /node_modules/express/lib/response.js:1003
// if (err) return req.next(err);
// ^
// TypeError: req.next is not a function
router.get('/articles', function(req, res, next) {
admin.database().ref('articles').orderByChild('timestamp').on('child_added', function (snapshot) {
let articles = snapshot.val();
console.log(articles);
res.render('articles', articles);
});
});
I don't get what I'm doing wrong. I see that the two firebase database calls are different, one is an once and then (so it must be a promise..?) and the other is a on (so i suppose it's just a normal callback...).
我不知道我做错了什么。我看到两个firebase数据库调用是不同的，一个是一次然后（所以它必须是一个承诺......？）而另一个是on（所以我想它只是一个正常的回调......）。
Do you have any idea on why is happening here? Sorry if this is obvious but I'm somewhat of a beginner..
你对这里发生的原因有什么看法吗？对不起，如果这是显而易见的，但我有点初学者..
1 个解决方案
#1
2
When you execute a query against the Firebase Database, there will potentially be multiple results. So the snapshot contains a list of those results. Even if there is only a single result, the snapshot will contain a list of one result.
对Firebase数据库执行查询时，可能会有多个结果。因此快照包含这些结果的列表。即使只有一个结果，快照也会包含一个结果的列表。
So in your first example snapshot holds they things: the keys of the matching nodes, their values, and the ordering between them. When you call snapshot.val() this data is converted into a regular JSON object, which doesn't have space for all three pieces of information. At this point the ordering information is dropped.
因此，在您的第一个示例中，快照包含它们：匹配节点的键，它们的值以及它们之间的顺序。当您调用snapshot.val（）时，此数据将转换为常规JSON对象，该对象没有空间容纳所有三条信息。此时，订购信息被删除。
The solution is to use snapshot.forEach() to loop over the matching nodes in the correct order.
解决方案是使用snapshot.forEach（）以正确的顺序循环匹配的节点。
admin.database().ref('articles').orderByChild('timestamp').once('value').then(function (snapshot) {
var articles = [];
snapshot.forEach(function(articleSnapshot)
articles.push(snapshot.val());
});
console.log(articles);
res.render('articles', articles);
});
#1
2
When you execute a query against the Firebase Database, there will potentially be multiple results. So the snapshot contains a list of those results. Even if there is only a single result, the snapshot will contain a list of one result.
对Firebase数据库执行查询时，可能会有多个结果。因此快照包含这些结果的列表。即使只有一个结果，快照也会包含一个结果的列表。
So in your first example snapshot holds they things: the keys of the matching nodes, their values, and the ordering between them. When you call snapshot.val() this data is converted into a regular JSON object, which doesn't have space for all three pieces of information. At this point the ordering information is dropped.
因此，在您的第一个示例中，快照包含它们：匹配节点的键，它们的值以及它们之间的顺序。当您调用snapshot.val（）时，此数据将转换为常规JSON对象，该对象没有空间容纳所有三条信息。此时，订购信息被删除。
The solution is to use snapshot.forEach() to loop over the matching nodes in the correct order.
解决方案是使用snapshot.forEach（）以正确的顺序循环匹配的节点。
admin.database().ref('articles').orderByChild('timestamp').once('value').then(function (snapshot) {
var articles = [];
snapshot.forEach(function(articleSnapshot)
articles.push(snapshot.val());
});
console.log(articles);
res.render('articles', articles);
});