[英]How to get count of elements in document array - MongoDB?
I have the following MongoDB collection (JSON): 我有以下MongoDB集合(JSON):
{
"_id" : ObjectId("570185458351bbac27bc9a20"),
"email" : "test@gmail.com",
"applicants" : [
{
"id" : "570724e4ae4f8a5026156999",
"email" : "a@gmail.com",
},
{
"id" : "570724e4ae4f8a5026156333",
"email" : "a2@gmail.com",
},
{
"id" : "570724e4ae4f8a5026156111",
"email" : "a3@gmail.com",
},
{
"id" : "570724e4ae4f8a5026156222",
"email" : "a4@gmail.com",
}
],
},
{
"_id" : ObjectId("570185458351bbac27bc9a20"),
"email" : "test@gmail.com",
"applicants" : [
{
"id" : "570724e4ae4f8a5026156555",
"email" : "a@gmail.com",
},
{
"id" : "570724e4ae4f8a5026156666",
"email" : "a2@gmail.com",
},
],
},
{
"_id" : ObjectId("570185458351bbac27bc9a20"),
"email" : "test2@gmail.com",
"applicants" : [
{
"id" : "570724e4ae4f8a5026156555",
"email" : "a@gmail.com",
},
{
"id" : "570724e4ae4f8a5026156666",
"email" : "a2@gmail.com",
},
],
}
I would like to get the count of the elements in all arrays of the of the document where the email = test@gmail.com. 我想获取电子邮件= test@gmail.com的文档的所有数组中元素的数量。 How can I go about getting that count?
我该如何获得该计数?
I am using the following to get the number of documents with email test@gmail.com using this: 我正在使用以下方法通过以下方式通过电子邮件test@gmail.com获取文档数量:
collection.count({"email" : tmpEmail}, function (err, count) {
res.json(count);
console.log("Number: " + count);
});
How can I go ahead and count the number of elements in all applicant arrays for the documents where the email is test@gmail.com? 我该如何继续计算电子邮件为test@gmail.com的文档的所有申请人数组中的元素数? The could for the example above would be: 6.
上面的示例可能是:6。
As per one of the answers I modified my query to the following: 根据答案之一,我将查询修改为以下内容:
Answer 1: 答案1:
collection.aggregate(
{$match: {"email": req.user.username, "status" : "true"}},
{$unwind: "$applicants"},
{$group: {_id:null, count: {$sum :1}}, function (err, count) {
res.json(count);
console.log("Number of New Applicants: " + count);
}
});
Answer 2: 答案2:
collection.aggregate(
[{$match:{"email" : req.user.username, "status" : "true"}},
{$project:{_id:0, email:1, totalApplicants:{$size:"$applicants"}}},
{$group:{_id:"$employer", count:{$sum:"$totalApplicants"}}}],
function (err, count){
res.json(count);
console.log("Number of New Applicants: " + count);
});
You can use an aggregate query instead: 您可以改用汇总查询:
collection.aggregate(
[{$match: {"email": req.user.username, "status" : "true"}},
{$unwind: "$applicants"},
{$group: {_id:null, count: {$sum :1}}}], function (err, result) {
console.log(result);
console.log("Number of New Applicants: " + result[0].count);
if(result.length > 0)
res.json(result[0]);
else
res.json({count:0});
}
});
This will result you in one document where count will have your required result 这将使您得到一份文件,在此文件中,计数将具有所需的结果
This may require to write a aggregation since you need to count the size of applicants array grouped by email: 这可能需要编写汇总,因为您需要计算按电子邮件分组的申请人数组的大小:
Here is the equivalent mongodb query that returns the expected email with count: 以下是等效的mongodb查询,该查询返回带有count的预期电子邮件:
db.yourCollection.aggregate(
[{$match:{"email" : "test@gmail.com"}},
{$project:{_id:0, email:1,totalEmails:{$size:"$applicants"}}},
{$group:{_id:"$email", count:{$sum:"$totalEmails"}}}])
This returns { "_id" : "test@gmail.com", "count" : 6 }
这将返回
{ "_id" : "test@gmail.com", "count" : 6 }
You may need to change this according to your code. 您可能需要根据您的代码进行更改。
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