MongoDB中$ in的结果顺序,例如MySQL字段('_id',...) [英] Order of results in MongoDB with $in like MySQL field('_id', ...)
问题描述
我正在使用MongoDB构建一个非常漂亮的趋势"帖子算法.由于该算法会消耗大量时间,因此我在cron任务中执行了我的算法,然后缓存了帖子ID的排序数组.像这样(PHP vardump):
"trending" => array("548ac5ce05ea675e468b4966", "5469c6d5039069a5030041a7", ...)
要点是,我找不到使用MongoDB以此顺序检索它们的任何方法. 使用MySQL只需完成以下操作即可:
SELECT * FROM posts
ORDER BY FIELD(_id, '548ac5ce05ea675e468b4966', '5469c6d5039069a5030041a7',...)
到目前为止,我尝试的是可以找到的东西 有人做到了吗,甚至不知道从哪里开始? 谢谢! 我来自您链接的SO帖子.我发现是使用MongoDB提供的 $$ ROOT 变量. /p>
我的代码如下: 请注意,我个人不确定该 I'm building a quite fancy "trending" posts algorithm using MongoDB. As the algorithm consumes quite a lot of time, I'm executing my algorithm in a cron task and then I cache a sorted array of posts ids. Like this (PHP vardump): The point is that I can not find any way to retrieve them in that order using MongoDB.
Using MySQL it would be done just by doing: What I tried so far is what it can be founde here, so now I am able to retrieve an sorted list with the weight, but not the posts. The response is like this: Does anyone has achieved this or even know where to start? Thank you! I'm coming from the SO post you linked. What I found was to use the $$ROOT variable provided by MongoDB. My code looks like this: Note that I'm personally not exactly sure of what's going on in that 这篇关于MongoDB中$ in的结果顺序,例如MySQL字段('_id',...)的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!var ids = [456, 123, 789]
, stack = []
;
// Note that `i` is decremented here, not incremented like
// in the linked SO post. I think they have a typo.
for (var i = ids.length-1; i > 0; i--) {
var rec = {
$cond: [
{$eq: ['$_id', ids[i - 1]]},
i
]
};
if (stack.length === 0) {
rec.$cond.push(i + 1);
}
else {
var lval = stack.pop();
rec.$cond.push(lval);
}
stack.push(rec);
}
var pipeline = [
{$match: {
_id: {$in: ids}
}},
{$project: {
weight: stack[0],
data: '$$ROOT' // This will give you the whole document.
}},
{$sort: {weight: 1}}
];
Posts.aggregate(pipeline, function (err, posts) {
if (err) return next();
// Use Underscore to grab the docs stored on `data` from above.
res.json(_.pluck(posts, 'data'));
});
for
循环中用于构建查询的情况. :-P因此,大多数功劳应该归功于他们.另外我还不确定是否将虚拟字段(如果您使用的是Mongoose,就象我一样)包含在此处,但我怀疑没有."trending" => array("548ac5ce05ea675e468b4966", "5469c6d5039069a5030041a7", ...)
SELECT * FROM posts
ORDER BY FIELD(_id, '548ac5ce05ea675e468b4966', '5469c6d5039069a5030041a7',...)
{
"result" : [
{
"_id" : ObjectId("548ac5ce05ea675e468b4966"),
"weight" : 1
},
{
"_id" : ObjectId("5469c6d5039069a5030041a7"),
"weight" : 2
}
],
"ok" : 1
}
var ids = [456, 123, 789]
, stack = []
;
// Note that `i` is decremented here, not incremented like
// in the linked SO post. I think they have a typo.
for (var i = ids.length-1; i > 0; i--) {
var rec = {
$cond: [
{$eq: ['$_id', ids[i - 1]]},
i
]
};
if (stack.length === 0) {
rec.$cond.push(i + 1);
}
else {
var lval = stack.pop();
rec.$cond.push(lval);
}
stack.push(rec);
}
var pipeline = [
{$match: {
_id: {$in: ids}
}},
{$project: {
weight: stack[0],
data: '$$ROOT' // This will give you the whole document.
}},
{$sort: {weight: 1}}
];
Posts.aggregate(pipeline, function (err, posts) {
if (err) return next();
// Use Underscore to grab the docs stored on `data` from above.
res.json(_.pluck(posts, 'data'));
});
for
loop to build the query. :-P So most credit should go to them. Also I'm not sure yet if virtual fields (if you're using Mongoose, as I am) would be included here, but I suspect not.