Consider this code. I have this query in a 3T Studio aggregate query.
{
"book.newpublisheddate": {$subtract : [ {$date: "book.published"}, {$date: "1970-01-01T00:00:00.000+0000"}] }
}
I cannot use code like {$subtract : [ "book.published", new Date()] } because it says it is not valid json. I am using mongo 3.6.13.
Using this collection:
> db.test.find()
{
"_id": 0,
"book": {
"published": ISODate("2019-08-04T22:49:14.416Z")
}
}
This aggregation works:
> db.test.aggregate([
{$project:
{dateDiff: {$subtract: ['$book.published', ISODate('1970-01-01')] }}}
])
{ "_id": 0, "dateDiff": NumberLong("1564958954416") }
Note that you don't need to surround book.published inside a $date, rather just use $book.published. You also need ISODate('1970-01-01').
This works inside Studio3T "shell mode" and inside the mongo shell.
No idea where do you want to use {$subtract : [ "book.published", new Date()] }. Assuming it is mongo shell - most likely you are missing a dollar sign before "book.published". Try "$book.published" - use $ to reference fields.
Related
new to Mongo. Trying to group across different sub fields of a document based on a condition. The condition is a regex on a field value. Looks like -
db.collection.aggregate([{
{
"$group": {
"$cond": [{
"upper.leaf": {
$not: {
$regex: /flower/
}
}
},
{
"_id": {
"leaf": "$upper.leaf",
"stem": "$upper.stem"
}
},
{
"_id": {
"stem": "$upper.stem",
"petal": "$upper.petal"
}
}
]
}
}])
Using api v4.0: cond in the docs shows - { $cond: [ <boolean-expression>, <true-case>, <false-case> ] }
The error I get with the above code is - "Syntax error: dotted field name 'upper.leaf' can not used in a sub object."
Reading up on that I tried $let to re-assign the dotted field name. But started to hit various syntax errors with no obvious issue in the query.
Also tried using $project to rename the fields, but got - Field names may not start with '$'
Thoughts on the best approach here? I can always address this at the application level and split my query into two but it's attractive potentially to solve it natively in mongo.
$group syntax is wrong
{
$group:
{
_id: <expression>, // Group By Expression
<field1>: { <accumulator1> : <expression1> },
...
}
}
You tried to do
{
$group:
<expression>
}
And even if your expression resulted in the same code, its invalid syntax for $group (check from the documentation where you are allowed to use expressions)
One other problem is that you use the query operator for regex, and not the aggregate regex operators (you can't do that, if you aggregate you can use only aggregate operators, only $match is the exception that you can use both if you add $expr)
You need this i think
[{
"$group" : {
"_id" : {
"$cond" : [ {
"$not" : [ {
"$regexMatch" : {
"input" : "$upper.leaf",
"regex" : "/flower/"}}]},
{"leaf" : "$upper.leaf","stem" : "$upper.stem"},
{"stem" : "$upper.stem","petal" : "$upper.petal"}]
}
}}]
Its similar code, but expression gets as value of the "_id" and $regexMatch
is used that is aggregate operator.
I didnt tested the code.
Given collection:
{
"_id" : "1.1000038",
"recomendation" : [
"1.6739718"
]
}
/* 2 */
{
"_id" : "1.1000069",
"recomendation" : [
"1.9185509",
"1.9051998",
"1.9034279",
"1.8288046",
"1.8152670",
"1.858775",
"1.6224229",
"1.4591674",
"1.3862464",
"1.3427739",
"1.3080062",
"1.3003608",
"1.1694619",
"1.1634683",
"1.1590664",
"1.1524146",
"1.754599",
"1.700837",
"1.763617"
]
}
I need to query the MongoDB for a list of values and get the first element of the list of values
here is the query by mongo syntax
db.getCollection('similar_articles').find({"_id":{$in:["1.1000069","1.1000038"]}})
I don't want to filter it on the python side because it's can be too big.
I didn't find any documentation on it
desire output:
Pandas DataFrame
_id recom
1.1000038 1.6739718
1.1000069 1.9185509
I don't know pymongo so well, but you need this query:
First $match by _ids into the arreay (this is like the find you have).
And later use $project to create the field recom (you can use "recomendation" to overwrite the existing field) and set the value as the first into the array.
db.collection.aggregate([
{
"$match": { "_id": { "$in": [ "1.1000069", "1.1000038" ] } }
},
{
"$project": { "recom": { "$arrayElemAt": [ "$recomendation", 0 ] } }
}
])
Example here
Looking the doumentation it seems you only need to copy and paste this query.
I tried to show particular columns in mongodb colletion.but its not working.how to show particular columnns.
user_collection
[{
"user_name":"hari",
"user_password":"123456"
}]
find_query
db.use_collection.find({},{projection:{user_name:1}})
I got output
[{
"user_name":"hari",
"user_password":"123456"
}]
Excepted output
[{
"user_name":"hari",
}]
Try:
db.use_collection.find({}, {user_name:1, _id: 0 })
In that way you get the field user_name and exclude the _id.
Extra info:
project fields and project fields excluding the id
With aggregate:
db.use_collection.aggregate( [ { $project : { _id: 0, user_name : 1 } } ] )
You can try this
Mongo query:
db.users.aggregate([
{
"$project":
{
"_id": 0,
"first_name": 1,
}
}
])
Or in ruby (Mongoid)
User.collection.aggregate(
[
"$project":
{
"_id": 0,
"first_name": 1,
}
]
)
If you try to inspect the record, you can convert it into an array first (e.g. User.collection.aggregate(...).to_a)
You can use the official mongodb reference when writing in Mongoid, usually you just need to use double quote on the property name on the left hand side, to make it work on Mongoid.
Try:
db.use_collection.find({}, {user_password:0, _id: 0 ,user_name:1 })
i'm trying to calculate a value within a given polygon:
acutally i'm using this pipeline:
'aggregation': {
'pipeline': [
{ "$match" : { "location" : "$loc" } },
{ "$group": { "_id": 'Average', "AvgField": { "$avg": "$myavgvalue" } , "count": {"$sum": 1} } },
]
}
but it seems the $match is ignoring the geospatial index.
any idea how i can do this ?
best regards
Harald
You need to use the ?aggregate={"$loc": ...} query syntax, so the parser knows it has to invoke the aggregation engine instead of the standard query parser. This example comes straight from the documentation:
$ curl -i http://example.com/posts?aggregate={"$value": 2}
Also, make sure the proper geo index has been added to the collection. Eve won't automatically do that for you, unless you explicitly choose to do so by setting mongo_indexes.
Mongo DB: I'm looking to make one query to return both the first and last element of an array. I realize that I can do this multiple queries, but I would really like to do it with one.
Assume a collection "test" where each objects has an array "arr" of numbers:
db.test.find({},{arr:{$slice: -1},arr:{$slice: 1}});
This will result in the following:
{ "_id" : ObjectId("xxx"), "arr" : [ 1 ] } <-- 1 is the first element
Is there a way to maybe alias the results? Similar to what the mysql AS keyword would allow in a query?
This is not possible at the moment but will be with the Aggregation Framework that's in development now if I understand your functional requirement correctly.
You have to wonder about your schema if you have this requirement in the first place though. Are you sure there isn't a more elegant way to get this to work by changing your schema accordingly?
This can be done with the aggregation framework using the operators $first and $last as follows:
db.test.aggregate([
{ '$addFields': {
'firstElem': { '$first': '$arr' },
'lastElem': { '$last': '$arr' }
} }
])
or using $slice as
db.test.aggregate([
{ '$addFields': {
'firstElem': { '$slice': [ '$arr', 1 ] },
'lastElem': { '$slice': [ '$arr', -1 ] }
} }
])