Trying to query Mongo, and get 1 field of element 0, inside a document, namely emails[0].address:
Here's a sample (truncated) document structure:
{
"_id" : "dfadgfe266reh",
"emails" : [
{
"address" : "email#domain.com",
"verified" : false
}
]
}
And my query (truncated) is like this:
{
fields: {
'emails.0.address': {
address: 1
}
}
}
However, when I run this, I get an empty object array, namely emails:[{}]
But if I change the selector to 'emails.address' it will give me the actual email address -- the problem is I only want emails[0].address
What am I doing wrong?
To get the required document you need a project document with two attributes. First one, as #Veeram mentioned, slices the array and second to specify an attribute from the embedded document in the array. See code:
db.collection.find( {}, { "emails": { $slice: 1 } , "emails.address": 1} );
You can use $ in projection:
.find({"emails.address":{$exists:true}}, {"emails.$.address":1})
Related
I have a processes document with a nested attachments array, I want to return get the fileName with the processes _id and attachment _id.
I have tried many options, my latest attempt still return all items from the attachments array. I only want the attachment that matches the attachment id past in.
db.getCollection('processes').find(
{$and: [ { "_id" : ObjectId("5a9455d7854cd987a40b1ba4") },
{ "attachments._id" : ObjectId("5a983da6201ba5a2302fb38f") }]},
{'attachments._id': 1, 'attachments.fileName': 1}
)
Any suggestion is greatly appreciated, thanks!
You can use $elemMatch in projection to get only one filtered subdocument from nested array:
db.getCollection('processes').find(
{ "_id" : ObjectId("5a9455d7854cd987a40b1ba4") },
{ attachments: { $elemMatch: { _id: ObjectId("5a983da6201ba5a2302fb38f") } } } )
I have the following document:
{
"_id" : ObjectId("5720bd01232ac527623f2889"),
"planes" : [
{
"name" : "plane1",
"wings" : [
{
"name" : "rightDown"
},
{
"name" : "rightUp"
}
]
},
{
"name" : "plane2",
"wings" : [
{
"name" : "leftUp",
},
{
"name" : "leftDown",
}
]
}
]
}
I want to update an object in an array nested in an another array, without using the array index.
In my example, 'plane2' with the property 'wing' named 'leftDown'. Is it possible ?
db.planes.update({
planes: {
$elemMatch: {
wings: {
$elemMatch: {
name: 'leftUp'
}
}
}
}
},
// It would be wonderful if I the $set would look like this,
// but the error is:
// "Too many positional (i.e. '$') elements found in path 'planes.$.wings.$'"
//
// It seems that $ holds only the value of the first nested
// object in the array
{
$set: {
'planes.$.wings.$': {
name: 'leftMagic'
}
}
})
MongoDb 3.2 documentation says:
The positional $ operator cannot be used for queries which traverse more than one array, such as queries that traverse arrays nested within other arrays, because the replacement for the $ placeholder is a single value
But I'm still waiting for that miracle ..
Are there any other clean/beautiful ways to do the update in a single shoot ?
Sadly no, the positional operator can only hold a single value. I don't think you can perform this update in a single shot with your current data structure.
You could perform one lookup to get the first array index, then a second with the positional operator, but at that point you could just traverse the array and resave the document.
With a little restructuring of your collections you could get the update down to a single operation. Check out MongooseJS populate.
I would like to ranked in descending order a list of documents in array names via their number value.
Here's the structure part of my collection :
_id: ObjectId("W")
var1: "X",
var2: "Y",
var3: "Z",
comments: {
names: [
{
number: 1;
},
{
number: 3;
},
{
number: 2;
}
],
field: Y;
}
but all my request with db.collection.find().sort( { "comments.names.number": -1 } ) doesn't work.
the desired output sort is :
{ "_id" : ObjectId("W"), "var1" : "X", "var3" : "Z", "comments" : { [ { "number" : 3 }, { "number" : 2 },{ "number" : 1 } ], "field": "Y" } }
Can you help me?
You need to aggregate the result, as below:
Unwind the names array.
Sort the records based on comments.names.number in descending
order.
Group the records based on the _id field.
project the required structure.
Code:
db.collection.aggregate([
{$unwind:"$comments.names"},
{$sort:{"comments.names.number":-1}},
{$group:{"_id":"$_id",
"var1":{$first:"$var1"},
"var2":{$first:"$var2"},
"var3":{$first:"$var3"},
"field":{$first:"$comments.field"},
"names":{$push:"$comments.names"}}},
{$project:{"comments":{"names":"$names","field":"$field"},"var1":1,
"var2":1,"var3":1}}
],{"allowDiskUse":true})
If your collection is large, you might want to add a $match criteria in the beginning of the aggregation pipeline to filter records or use (allowDiskUse:true), to facilitate sorting large number of records.
db.collection.aggregate([
{$match:{"_id":someId}},
{$unwind:"$comments.names"},
{$sort:{"comments.names.number":-1}},
{$group:{"_id":"$_id",
"var1":{$first:"$var1"},
"var2":{$first:"$var2"},
"var3":{$first:"$var3"},
"field":{$first:"$comments.field"},
"names":{$push:"$comments.names"}}},
{$project:{"comments":{"names":"$names","field":"$field"},"var1":1,
"var2":1,"var3":1}}
])
What The below query does:
db.collection.find().sort( { "comments.names.number": -1 } )
is to find all the documents, then sort those documents based on the number field in descending order. What this actually does is for each document get the comments.names.number field value which is the largest, for each document. And then sort the parent documents based on this number. It doesn't manipulate the names array inside each parent document.
You need update document for sort an array.
db.collection.update(
{ _id: 1 },
{
$push: {
comments.names: {
$each: [ ],
$sort: { number: -1 }
}
}
}
)
check documentation here:
http://docs.mongodb.org/manual/reference/operator/update/sort/#use-sort-with-other-push-modifiers
MongoDB queries sort the result documents based on the collection of fields specified in the sort. They do not sort arrays within a document. If you want the array sorted, you need to sort it yourself after you retrieve the document, or store the array in sorted order. See this old SO answer from Stennie.
I have a collection users as follows:
{ "_id" : ObjectId("51780f796ec4051a536015cf"), "userId" : "John" }
{ "_id" : ObjectId("51780f796ec4051a536015d0"), "userId" : "Sam" }
{ "_id" : ObjectId("51780f796ec4051a536015d1"), "userId" : "John1" }
{ "_id" : ObjectId("51780f796ec4051a536015d2"), "userId" : "john2" }
Now I am trying to write a code which can provides suggestions of a userId to user in case id provided by user already exists in DB. In same routine I just append values from 1 to 5 to the for example in case user have selected userId to be John, suggested user name array that needs to be checked for Id in database will look like this
[John,John1,John2,John3,John4,John5].
Now I just want to execute it against Db and to find out which of the suggested values do not exist in DB. So instead of selecting any document, I want to select values within suggested array which do not exist for users collection.
Any pointers are highly appreciated.
Your general approach here is you want to find the "distinct" values for the "userId's" that already exist in your collection. You then compare these to your input selection to see the difference.
var test = ["John","John1","John2","John3","John4","John5"];
var res = db.collection.aggregate([
{ "$match": { "userId": { "$in": test } }},
{ "$group": { "_id": "$userId" }}
]).toArray();
res.map(function(x){ return x._id });
test.filter(function(x){ return res.indexOf(x) == -1 })
The end result of this is the userId's that do not match in your initial input:
[ "John2", "John3", "John4", "John5" ]
The main operator there is $in which takes an array as the argument and compares those values against the specified field. The .aggregate() method is the best approach, there is a shorthand mapReduce wrapper in the .distinct() method which directly produces just the values in the array, removing the call to a function like .map() to strip out the values for a given key:
var res = db.collection.distinct("userId",{ "userId": { "$in": test } })
It should run notably slower though, especially on large collections.
Also do not forget to index your "userId" and likely you want this to be "unique" anyway so you really just want the $match or .find() result:
var res = db.collection.find({ "$in": test }).toArray()
I want to combine two mongodb collections.
Basically I have a collection containing documents that reference one document from another collection. Now I want to have this as a inline / nested field instead of a separate document.
So just to provide an example:
Collection A:
[{
"_id":"90A26C2A-4976-4EDD-850D-2ED8BEA46F9E",
"someValue": "foo"
},
{
"_id":"5F0BB248-E628-4B8F-A2F6-FECD79B78354",
"someValue": "bar"
}]
Collection B:
[{
"_id":"169099A4-5EB9-4D55-8118-53D30B8A2E1A",
"collectionAID":"90A26C2A-4976-4EDD-850D-2ED8BEA46F9E",
"some":"foo",
"andOther":"stuff"
},
{
"_id":"83B14A8B-86A8-49FF-8394-0A7F9E709C13",
"collectionAID":"90A26C2A-4976-4EDD-850D-2ED8BEA46F9E",
"some":"bar",
"andOther":"random"
}]
This should result in Collection A looking like this:
[{
"_id":"90A26C2A-4976-4EDD-850D-2ED8BEA46F9E",
"someValue": "foo",
"collectionB":[{
"some":"foo",
"andOther":"stuff"
},{
"some":"bar",
"andOther":"random"
}]
},
{
"_id":"5F0BB248-E628-4B8F-A2F6-FECD79B78354",
"someValue": "bar"
}]
I'd suggest something simple like this from the console:
db.collB.find().forEach(function(doc) {
var aid = doc.collectionAID;
if (typeof aid === 'undefined') { return; } // nothing
delete doc["_id"]; // remove property
delete doc["collectionAID"]; // remove property
db.collA.update({_id: aid}, /* match the ID from B */
{ $push : { collectionB : doc }});
});
It loops through each document in collectionB and if there is a field collectionAID defined, it removes the unnecessary properties (_id and collectionAID). Finally, it updates a matching document in collectionA by using the $push operator to add the document from B to the field collectionB. If the field doesn't exist, it is automatically created as an array with the newly inserted document. If it does exist as an array, it will be appended. (If it exists, but isn't an array, it will fail). Because the update call isn't using upsert, if the _id in the collectionB document doesn't exist, nothing will happen.
You can extend it to delete other fields as necessary or possibly add more robust error handling if for example a document from B doesn't match anything in A.
Running the code above on your data produces this:
{ "_id" : "5F0BB248-E628-4B8F-A2F6-FECD79B78354", "someValue" : "bar" }
{ "_id" : "90A26C2A-4976-4EDD-850D-2ED8BEA46F9E",
"collectionB" : [
{
"some" : "foo",
"andOther" : "stuff"
},
{
"some" : "bar",
"andOther" : "random"
}
],
"someValue" : "foo"
}
Sadly mapreduce can't produce full documents.
https://jira.mongodb.org/browse/SERVER-2517
No idea why despite all the attention, whining and upvotes they haven't changed it. So you'll have to do this manually in the language of your choice.
Hopefully you've indexed 'collectionAID' which should improve the speed of your queries. Just write something that goes through your A collection one document at a time, loading the _id and then adding the array from Collection B.
There is a much faster way than https://stackoverflow.com/a/22676205/1578508
You can do it the other way round and run through the collection you want to insert your documents in. (Far less executions!)
db.collA.find().forEach(function (x) {
var collBs = db.collB.find({"collectionAID":x._id},{"_id":0,"collectionA":0});
x.collectionB = collBs.toArray();
db.collA.save(x);
})