I have the below structure for my collection:
{
"price":123,
"totalPrices": [
{
"totPrice":123
}
]
}
I am trying to query for all the documents in my collection where price is not equals to totalPrice.totPrice (so above should not be returned).
But it keeps returning the documents which have equal prices as well (such as above sample).
This is the query I'm using:
{
$where : "this.price!== this.totalPrices.totPrice",
totalPrice:{$size:1}
}
What am I doing wrong :(
First, you need to match the size of the array totalPrices is equal to 1. Second, you need to unwind the totalPrices, since it's an array field. Last, you should match the equality of price and totalPrices.totPrice. Try the below code:
db.collection.aggregate([
{
$match: {
$expr: {
$eq: [
{
$size: "$totalPrices"
},
1
]
}
}
},
{
$unwind: "$totalPrices"
},
{
$match: {
$expr: {
$ne: [
"$price",
"$totalPrices.totPrice"
]
}
}
}
])
MongoPlayGroundLink
Related
I have a collection with documents like this one:
{
f1: {
firstArray: [
{
secondArray: [{status: "foo1"}, {status: "foo2"}, {status: "foo3"}]
}
]
}
}
My expected result includes documents that have at least one item in firstArray, which is last object status on the secondArray is included in an input array of values (eg. ["foo3"]).
I don't must use aggregate.
I tried:
{
"f1.firstArray": {
$elemMatch: {
"secondArray.status": {
$in: ["foo3"],
},
otherField: "bar",
},
},
}
You can use an aggregation pipeline with $match and $filter, to keep only documents that their size of matching last items are greater than zero:
db.collection.aggregate([
{$match: {
$expr: {
$gt: [
{$size: {
$filter: {
input: "$f1.firstArray",
cond: {$in: [{$last: "$$this.secondArray.status"}, ["foo3"]]}
}
}
},
0
]
}
}
}
])
See how it works on the playground example
If you know that the secondArray have always 3 items you can do:
db.collection.find({
"f1.firstArray": {
$elemMatch: {
"secondArray.2.status": {
$in: ["foo3"]
}
}
}
})
But otherwise I don't think you can check only the last item without an aggregaation. The idea is that a regular find allows you to write a query that do not use values that are specific for each document. If the size of the array can be different on each document or even on different items on the same document, you need to use an aggregation pipeline
Mongodb: 4.0.13
I'm having troubles in understand and get working $expr with arrays.
Let' start and create a new collection (dbRepeatElement) with following document:
db.testRepeatElement.insert([
{
"data" : {
"FlsResSemires_2" : {
"Sospensione" : [
{
"DataInizio" : 1548806400000,
"DataFine" : 1549065600000,
"Motivazione" : "1"
}
]
}
},
"derived" : {
"DATAFINEANNORIFERIMENTO" : 1609372800000,
"regione190" : "190",
"REGAOEROG" : "190209820300",
"REGASLEROG" : "190209"
}
}
])
In a bigger aggregation, following part is not working:
db.testRepeatElement.aggregate([
{
$match: {
$expr: {
$gt: ["$data.FlsResSemires_2.Sospensione.DataInizio", "$derived.DATAFINEANNORIFERIMENTO"]
}
}
}
])
Result: return a match ( wrong! just check dates)
Reading mongodb documentation seems to be, using combination with arrays, aggregation and $expr does not return expected result and you have to specify with element of the array you want to check, like:
db.testRepeatElement.aggregate([
{
$match: {
$expr: {
$gt: ["$data.FlsResSemires_2.0.Sospensione.DataInizio", "$derived.DATAFINEANNORIFERIMENTO"]
}
}
}
])
Result: return no match (right!)
Question: my requirement is to check every element in the array, so how to solve this, without using $unwind? Why there is this kind of result ?
The $filter aggregation operator is used to do the match operation on array elements. The following aggregation query will result only the Sospensione array elements which match the $gt condition:
db.testRepeatElement.aggregate( [
{
$addFields: {
"data.FlsResSemires_2.Sospensione": {
$filter: {
input: "$data.FlsResSemires_2.Sospensione",
cond: {
$gt: [ "$$this.DataInizio", "$derived.DATAFINEANNORIFERIMENTO" ]
}
}
}
}
},
{
$match: {
$expr: {
$gt: [ { $size: "$data.FlsResSemires_2.Sospensione" }, 0 ]
}
}
}
] ).pretty()
I'd like to retrieve for a specific user, his chats with unread messages.
Lets say I have a simplified chat model like that :
{
lastMessageAt: Date,
participants: [
{
user: String(id),
lastReadAt: Date
}
]
}
How can I achieve my query ?
I have tried several thing like with $elemMatch, but lastMessageAt is unknown at this level...
ChatDB.find({
'participants': {
$elemMatch: { user: '12345', lastReadAt: { $lt: '$lastMessageAt' } }
}
}
Thanks in advance for your help ! :)
$elemMatch operator will find those documents in ChatDB collection that have at least 1 element in participants that matches your criteria. Also my research ended with the conslusion that it is not yet possible to access other document field in $elemMatch operator. Anyway, if this is your goal, then you can use this query:
ChatDB.aggregate([
{
$match: {
"participants.user": "12345",
$expr: {
$lt: [
"$participants.lastReadAt",
"$lastMessageAt"
]
}
}
}
])
Mongo playground
If you also want to filter participants that really matched the criteria, then you need to add a projection stage:
ChatDB.aggregate([
{
$match: {
"participants.user": "12345",
$expr: {
$lt: [
"$participants.lastReadAt",
"$lastMessageAt"
]
}
}
},
{
$project: {
participants: {
$filter: {
input: "$participants",
as: "participant",
cond: {
$and: [
{
$eq: [
"$$participant.user",
"12345"
]
},
{
$lt: [
"$$participant.lastReadAt",
"$lastMessageAt"
]
}
]
}
}
}
}
}
])
Mongo playground
I have found the solution witch is to use the aggregator with the $unwind operator.
await ChatDB.aggregate([
{
$unwind: '$participants'
},
{
$match: {
'participants.user': '12345',
$expr: {
$lt: [
'$participants.lastReadAt',
'$lastMessageAt'
]
}
}
}]);
Hope this will be usefull
I've following mongodb query:
db
.getCollection("entries")
.find({
$and: [
{
"array.attribute_1": {
$exists: true,
$not: {
$size: 0
}
}
},
{
$or: [
{ "array.attribute_2": { $exists: true, $size: 0 } },
{ "array.attribute_2": { $exists: true, $eq: {} } }
]
},
]
})
And example of my document:
{
_id: 'foo',
array: [
{attribute_1: [], attribute_2: []},
{attribute_1: ['bar'], attribute_2: []}
]
}
In my understanding my query should find all entries that have at least one element within array that has existent and not empty attribute_1 and existent empty array or empty object attribute_2. However, this query finds all entries that has all elements within array that has existent and not empty attribute_1 and existent empty array or empty object attribute_2. As such, my foo entry won't be found.
What should be the correct formula for my requirements?
$find would find the first document with the matching criteria and in your case that first document contains all the arrays. You either need to use $project with $filter or aggregation with $unwind and $match.
Something like this:
db.collection.aggregate([
{ $unwind: "$array" },
{
$match: {
$and: [
{ "array.attribute_1.0": { $exists: true }},
{
$or: [
{ "array.attribute_2.0": { $exists: false } },
{ "array.attribute_2.0": { $eq: {} } }
]
}
]
}
}
])
You can see it working here
Also since you are trying to find out if array is empty and exists at the same time using .0 with $exists is a quick and one statement way to get the same result as with both $exists and $size.
I have these documents in my collection
{
id:1,
small:[{k:'A',v:1},{k:'B',v:2},{k:'D',v:3}],
big:[{k:'A',v:2},{k:'B',v:3},{k:'C',v:1},{k:'D',v:4}]
},
{
id:2,
small:[{k:'A',v:1},{k:'B',v:2},{k:'D',v:3}],
big:[{k:'A',v:2},{k:'B',v:3},{k:'C',v:1},{k:'D',v:4}]
},
{
id:3,
small:[{k:'A',v:1},{k:'B',v:2},{k:'D',v:3}],
big:[{k:'A',v:2},{k:'B',v:3},{k:'C',v:1},{k:'D',v:4}]
}
Now, I want to get the sum for each key in both lists. I want my output to look like this:
{k:'A',small:3, big:6},
{k:'B',small:6, big:9},
{k:'D',small:9, big:12}
Notice that the output did not contain the key 'C'. This is because I only want to output the keys that are existing in the 'small' list. What mongodb functions
should I use for this?
Thanks!
Try below aggregation:
db.col.aggregate([
{ $unwind: "$small" },
{ $unwind: "$big" },
{ $redact: {
$cond: {
if: { $eq: [ "$small.k", "$big.k" ] },
then: "$$KEEP",
else: "$$PRUNE"
}
}
},
{
$group: { _id: "$small.k", small: { $sum: "$small.v" }, big: { $sum: "$big.v" } }
},
{
$sort: { "_id": 1 }
}
])
In general we need to have only one small and big in each document (that's why double $unwind). Then we want to keep only documents where keys are equal. That's the moment where C is filtered out - has no pair in small and we're utilizing $redact for that. Aggregation is just a $group with $sum.