[英]Multiple mongoose count() queries to a MongoDB
first: me -> MongoNoob and I know this has already been asked in one or the other way, but I haven't found anything specific until now. 第一:我 - > MongoNoob,我知道这已经有过一种或另一种方式的问题,但到目前为止我还没有找到任何具体内容。 Let's say I have two Moongoose Models described like this:
假设我有两个这样描述的Moongoose模型:
var pollSchema = mongoose.Schema({
title: String,
choices: [{
content: String
}]
});
var choiceSchema = mongoose.Schema({
poll_id: mongoose.Schema.ObjectId,
option: Number
});
A UI shows the poll and when a user selects a choice, it is written into the choiceSchema
model. UI显示轮询,当用户选择一个选项时,它将写入
choiceSchema
模型。 Now I would like to create a 'statistic', telling me how many users selected option 1, option 2, option 3,.... I could simply fetch all choices for a poll with find
and generate the statistic in server code, but if I had a million user choices, I would have to deal with an array of the same size. 现在我想创建一个'统计',告诉我有多少用户选择了选项1,选项2,选项3,....我可以简单地获取
find
所有选项,并在服务器代码中生成统计信息,但是如果我有一百万用户选择,我将不得不处理相同大小的数组。 This cannot be right. 这不可能是对的。 I could however generate a query and use the
count()
method: 然而,我可以生成一个查询并使用
count()
方法:
var query = Choice.find({poll_id: someId}),
query.where('option', 1);
var resultForOption1;
query.count(function(err, count)) {
resultForOption1 = count;
});
How would I do this for multiple options and 'join' (haha) the results into an array? 我如何为多个选项执行此操作并将结果“加入”(哈哈)到数组中? Since this is all asynchronous I would have nest the calls, but that is not an option for a variable number of queries.
由于这是异步的,我会嵌套调用,但这不是可变数量的查询的选项。
Do I miss the wood for the trees :-)? 我想念树木:-)? Can somebody point me in the right direction?
有人能指出我正确的方向吗?
BR, Daniel BR,丹尼尔
You can use aggregate
to do this: 您可以使用
aggregate
来执行此操作:
Choice.aggregate(
{$group: {_id: {poll_id: '$poll_id', option: '$option'}, count: {$sum: 1}}}
).exec(...);
This will group the choices
collection docs by poll_id
and option
and count the occurrences of each, giving output that looks like: 这将按
poll_id
和option
对choices
集合文档进行poll_id
,并计算每个文档的出现次数,从而提供如下输出:
{
"result": [
{
"_id": {
"poll_id": 2,
"option": 3
},
"count": 1
},
{
"_id": {
"poll_id": 1,
"option": 2
},
"count": 2
},
{
"_id": {
"poll_id": 2,
"option": 2
},
"count": 1
},
{
"_id": {
"poll_id": 1,
"option": 1
},
"count": 1
}
],
"ok": 1
}
You can then use subsequent $group
and $project
stages in your aggregate
pipeline to further group and reshape the generated docs as needed. 然后,您可以在
aggregate
管道中使用后续$group
和$project
阶段,以根据需要进一步对生成的文档进行分组和重新整形。
If you want just iterate over the count
queries and do it easy and clean you can use a lib like co or even better, async: 如果你想迭代
count
查询并轻松清理你可以使用像co这样的lib甚至更好,async:
async.map({ "option":1 },{ "option":2 }], Choice.find, function(e, r){
// And you continue from here
});
Another option -better in my opinion-. 另一个选择 - 在我看来更好 - 。 is to use aggregate queries .
是使用聚合查询 。 You will learn more about mongoDB and should be more efficient.
您将了解有关mongoDB的更多信息,并且应该更有效率。 In the link I send to you the first example is almost what you want to do:
在我发给你的链接中,第一个例子几乎就是你想要做的:
(source: mongodb.org ) (来源: mongodb.org )
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