Check if embed exists - aggregation framework mongodb - mongodb

Question

This is my test collection:
>db.test.find()
{
"_id": ObjectId("54906479e89cdf95f5fb2351"),
"reports": [
{
"desc": "xxx",
"order": {"$id": ObjectId("53fbede62827b89e4f86c12e")}
}
]
},
{
"_id": ObjectId("54906515e89cdf95f5fb2352"),
"reports": [
{
"desc": "xxx"
}
]
},
{
"_id": ObjectId("549067d3e89cdf95f5fb2353"),
"reports": [
{
"desc": "xxx"
}
]
}
I want to count all documents and documents with order, so:
>db.test.aggregate({
$group: {
_id: null,
all: {
$sum: 1
},
order: {
$sum: {
"$cond": [
{
"$ifNull": ["$reports.order", false]
},
1,
0
]
}
}
}
})
and my results:
{
"result" : [
{
"_id" : null,
"all" : 3,
"order" : 3
}
],
"ok" : 1
}
but expected:
{
"result" : [
{
"_id" : null,
"all" : 3,
"order" : 1
}
],
"ok" : 1
}
It makes no difference what I'll put - "$reports.order", "$reports.xxx", etc, aggregation framework check only if the field reports exists, ignores embed.
$ifNull and $eq dosn't work with embeded documents?
Is any way to do something like this
db.test.find({"reports.order": {$exists: 1}})
in aggregation framework?
Sorry for my english and I hope that you understood what I want to show you :)

Answer 1

I think it doesn't work because the field "reports" contain an array, not an object.
I mean, your aggregation works as you expect in this collection:
>db.test.find()
{
"_id": ObjectId("54906479e89cdf95f5fb2351"),
"reports":
{
"desc": "xxx",
"order": {"$id": ObjectId("53fbede62827b89e4f86c12e")}
}
},
{
"_id": ObjectId("54906515e89cdf95f5fb2352"),
"reports":
{
"desc": "xxx"
}
},
{
"_id": ObjectId("549067d3e89cdf95f5fb2353"),
"reports":
{
"desc": "xxx"
}
}
Note that I removed the "[" and "]", so now it's an object, not an array (one-to-one relation).
Because you have array inside the "report" field, you need to unwind the array to output one document for each element. I suppose that if you have two "order" fields inside the "reports" array, you only wants to count it once. I mean:
"reports": [
{
"desc": "xxx",
"order": {"$id": ObjectId("53fbede62827b89e4f86c12e")},
"order": "yyy",
}
]
Should only count as one for the object final "order" sum.
In this case, you need to unwind, group by _id (because the previous example outputs two documents for the same _id) and then group again to count all documents:
db.test.aggregate([
{$unwind: '$reports'},
{$group:{
_id:"$_id",
order:{$sum:{"$cond": [
{
"$ifNull": ["$reports.order", false]
},
1,
0
]
}
}
}},
{$group:{
_id:null,
all:{$sum:1},
order: {
$sum:{
"$cond": [{$eq: ['$order', 0]}, 0, 1]
}
}
}}])
Maybe there is a shorter solution, but this works.