I have a collection with documents like this:
{
key : "bla"
list : [
{id:1},
{id:2}
]
}
How do I get this object: {id:1} ?
I tried a query like this: db.myCollection.find({"key":"bla", "list.id":1})
it finds the entry, but returns the complete document instead of only {id:1}
The $ operator is what you're looking for:
db.test.insert({key: "blah",list :[{id:1},{id:2}]})
db.test.find({'list.id' : 1},{'list.$': 1 })
#Returns:
#{ "_id" : ObjectId("521a78b342abf388fbaacf91"), "list" : [ { "id" : 1 } ] }
db.test.find({'list.id' : 2},{'list.$': 1 })
#Returns:
#{ "_id" : ObjectId("521a78b342abf388fbaacf91"), "list" : [ { "id" : 2 } ] }
If you don't need the _id of the document, you can exclude that too:
db.test.find({'list.id' : 2},{'list.$': 1 , _id: 0})
#Returns:
#{ "list" : [ { "id" : 2 } ] }
For more information, have a look at the documentation of the $ operator and read operations in general.
Related
I have the following document structure in a MongoDB collection :
{
"A" : [ {
"B" : [ { ... } ]
} ]
}
I'd like to update this to :
{
"A" : [ {
"B" : [ { ... } ],
"x" : [],
"y" : { ... }
} ]
}
In other words, I want the "x" and "y" fields to be added to the first element of the "A" array without loosing "B".
Ok as there is only one object in A array you could simply do as below :
Sample Collection Data :
{
"_id" : ObjectId("5e7c3cadc16b5679b4aeec26"),
A:[
{
B: [{ abc: 1 }]
}
]
}
Query :
/** Insert new fields into 'A' array's first object by index 0 */
db.collection.updateOne(
{ "_id" : ObjectId("5e7c3f77c16b5679b4af4caf") },
{ $set: { "A.0.x": [] , "A.0.y" : {abcInY :1 }} }
)
Output :
{
"_id" : ObjectId("5e7c3cadc16b5679b4aeec26"),
"A" : [
{
"B" : [
{
"abc" : 1
}
],
"x" : [],
"y" : {
"abcInY" : 1.0
}
}
]
}
Or Using positional operator $ :
db.collection.updateOne(
{ _id: ObjectId("5e7c3cadc16b5679b4aeec26") , 'A': {$exists : true}},
{ $set: { "A.$.x": [] , "A.$.y" : {abcInY :1 }} }
)
Note : Result will be the same, but functionally when positional operator is used fields x & y are inserted to first object of A array only when A field exists in that documents, if not this positional query would not insert anything (Optionally you can check A is an array condition as well if needed). But when you do updates using index 0 as like in first query if A doesn't exist in document then update would create an A field which is an object & insert fields inside it (Which might cause data inconsistency across docs with two types of A field) - Check below result of 1st query when A doesn't exists.
{
"_id" : ObjectId("5e7c3f77c16b5679b4af4caf"),
"noA" : 1,
"A" : {
"0" : {
"x" : [],
"y" : {
"abcInY" : 1.0
}
}
}
}
However, I think I was able to get anothe#whoami Thanks for the suggestion, I think your first solution should work. However, I think I was able to get another solution to this though I'm not sure if its better or worse (performance wise?) than what you have here. My solution is:
db.coll.update( { "_id" : ObjectId("5e7c4eb3a74cce7fd94a3fe7") }, [ { "$addFields" : { "A" : { "x" : [ 1, 2, 3 ], "y" : { "abc" } } } } ] )
The issue with this is that if "A" has more than one array entry then this will update all elements under "A" which is not something I want. Just out of curiosity is there a way of limiting this solution to only the first entry in "A"?
In a find query projection, fields I specify after the positional operator are ignored and the whole document is always returned.
'myArray.$.myField' : 1 behave exactly like 'myArray.$' : 1
the positional operator selects the right document. But this document is quite big. I would like to project only 1 field from it.
Exemple:
db.getCollection('match').find({"participantsData.id" : 0001}, { 'participantsData.$.id': 1, })
here the response I have
{
"_id" : "myid",
"matchCreation" : 1463916465614,
"participantsData" : [
{
"id" : 0001,
"plenty" : "of",
"other" : "fields",
"and" : "subdocuments..."
}
]
}
This is what I want
{
"_id" : "myid",
"matchCreation" : 1463916465614,
"participantsData" : [
{
"id" : 0001
}
]
}
Is it possible with mongo?
Yes it can be done in mongo
Please try the below query
db.getCollection('match').find(
{"participantsData.id" : 0001},
{"participantsData.id": 1, "matchCreation": 1 })
This will give you the below result
{
"_id" : "myid",
"matchCreation" : 1463916465614,
"participantsData" : [
{
"id" : 1
}
]
}
I need to be able to get a count of distinct 'transactions' the problem I'm having is that using .distinct() comes back with an error because the documents too large.
I'm not familiar with aggregation either.
I need to be able to group it by 'agencyID' as you see below there are 2 different agencyID's
I need to be able to count transactions where the agencyID is 01721487 etc
db.myCollection.distinct("bookings.transactions").length
this doesn't work as I need to be able to group by agencyID and if there are too many results I get an error saying it's too large.
{
"_id" : ObjectId("5624a610a6e6b53b158b4744"),
"agencyID" : "01721487",
"paxID" : "-530189664",
"bookings" : [
{
"bookingID" : "24232",
"transactions" : [
{
"tranID" : "001",
"invoices" : [
{
"invNum" : "1312",
"type" : "r",
"inv_date" : "20150723",
"inv_time" : "0953",
"inv_val" : -300
}
],
"tranType" : "Fee",
"tranDate" : "20150723",
"tranTime" : "0952",
"opCode" : "admin",
"udf_1" : "j s"
}
],
"acctID" : "acct11",
"agt_id" : "xy"
}
],
"title" : "",
"firstname" : "",
"surname" : "f bar"
}
I've also tried this but it didn't work for me.
thank you for text data -
this is something you could play with:
db.kieron.aggregate([{
$unwind : "$bookings"
}, {
$match : {
"bookings.transactions" : {
$exists : true,
$not : {
$size : 0
}
}
}
}, {
$group : {
_id : "$agencyID",
count : {
$sum : {
$size : "$bookings.transactions"
}
}
}
}
])
as there is nested array we need to unwind it first, and then we can check size of inner array.
Happy reporting!
I have a collection in which element has a list of objects. I would like to use $orderBy on a specific field on the first element of a list of objects that each document has.
For example:
each document represents a user, and each user has a list of sessions. I would like to sort the users on the date stored in the first session of the list.
Maybe something like { $orderby: { "sessions[0].timestamp" : 1 } } ?
Is this possible?
The operation you ask for is a simple one with .sort(). Perhaps you are not aware of the usage of "dot notation" with MongoDB
With the following documents as a minimal example:
{
"name" : "Fred",
"sessions" : [ { "timestamp" : ISODate("2014-06-05T10:38:24.371Z") } ]
}
{
"name" : "Barney",
"sessions" : [ { "timestamp" : ISODate("2014-06-05T10:38:34.557Z") } ]
}
Issue the following query:
db.users.find({},{ _id: 0}).sort({ "sessions.0.timestamp": -1 })
And get the ordered result by the first item of the array, timestamp field:
{
"name" : "Barney",
"sessions" : [ { "timestamp" : ISODate("2014-06-05T10:38:34.557Z") } ]
}
{
"name" : "Fred",
"sessions" : [ { "timestamp" : ISODate("2014-06-05T10:38:24.371Z") } ]
}
This is the first of 7 test/example documents, in collection "SoManySins."
{
"_id" : ObjectId("51671bb6a6a02d7812000018"),
"Treats" : "Sin1 = Gluttony",
"Sin1" : "Gluttony",
"Favourited" : "YES",
"RecentActivity" : "YES",
"GoAgain?" : "YeaSure."
}
I would like to be able to query to retrieve any info in any position,
just by referring to the position. The following document,
{
"_id" : ObjectId("51671bb6a6a02d7812000018"),
"Sin1" : "Gluttony",
"?????????" : "??????",
"RecentActivity" : "YES",
"GoAgain?" : "YeaSure."
}
One could retrieve whatever might be in the 3rd key~value
pair. Why should one have to know ahead of time what the
data is, in the key? If one has the same structure for the
collection, who needs to know? This way, you can get
double the efficiency? Like having a whole lot of mailboxes,
and your app's users supply the key and the value; your app
just queries the dbs' documents' arrays' positions.
Clara? finally? I hope?
The sample document you've provided is not saved as an array in BSON:
{
"_id" : ObjectId("51671bb6a6a02d7812000018"),
"Sin1" : "Gluttony",
"?????????" : "??????",
"RecentActivity" : "YES",
"GoAgain?" : "YeaSure."
}
Depending on the MongoDB driver you are using, the fields here are typically represented in your application code as an associative array or hash. These data structures are not order-preserving so you cannot assume that the 3rd field in a given document will correspond to the same field in another document (or even that the same field ordering will be consistent on multiple fetches). You need to reference the field by name.
If you instead use an array for your fields, you can refer by position or select a subset of the array using the $slice projection.
Example document with an array of fields:
{
"_id" : ObjectId("51671bb6a6a02d7812000018"),
"fields": [
{ "Sin1" : "Gluttony" },
{ "?????????" : "??????" },
{ "RecentActivity" : "YES" },
{ "GoAgain?" : "YeaSure." }
]
}
.. and query to find the second element of the fields array (a $slice with skip 1, limit 1):
db.SoManySins.find({}, { fields: { $slice: [1,1]} })
{
"_id" : ObjectId("51671bb6a6a02d7812000018"),
"fields" : [
{
"?????????" : "??????"
}
]
}
This is one way to Query and get back data when you may not
know what the data is, but you know the structure of the data:
examples in Mongo Shell, and in PHP
// the basics, setup:
$dbhost = 'localhost'; $dbname = 'test';
$m = new Mongo("mongodb://$dbhost");
$db = $m->$dbname;
$CursorFerWrites = $db->NEWthang;
// defining a set of data, creating a document with PHP:
$TheFieldGenerator = array( 'FieldxExp' => array(
array('Doc1 K1'=>'Val A1','Doc1 K2'=>'ValA2','Doc1 K3'=>'Val A3'),
array('Doc2 K1'=>'V1','Doc2 K2'=>'V2','Doc2 K3'=>'V3' ) ) ) ;
// then write it to MongoDB:
$CursorFerWrites->save($TheFieldGenerator);
NOTE : In the Shell : This produces the same Document:
> db.NEWthang.insert({"FieldxExp" : [
{"Doc1 K1":"Val A1","Doc1 K2":"Val A2","Doc1 K3":"Val A3"},
{"Doc2 K1":"V1", "Doc2 K2":"V2","Doc2 K3":"V3"}
]
})
#
Now, some mongodb Shell syntax:
> db.NEWthang.find().pretty()
{
"_id" : ObjectId("516c4053baa133464d36e836"),
"FieldxExp" : [
{
"Doc1 K1" : "Val A1",
"Doc1 K2" : "Val A2",
"Doc1 K3" : "Val A3"
},
{
"Doc2 K1" : "V1",
"Doc2 K2" : "V2",
"Doc2 K3" : "V3"
}
]
}
> db.NEWthang.find({}, { "FieldxExp" : { $slice: [1,1]} } ).pretty()
{
"_id" : ObjectId("516c4053baa133464d36e836"),
"FieldxExp" : [
{
"Doc2 K1" : "V1",
"Doc2 K2" : "V2",
"Doc2 K3" : "V3"
}
]
}
> db.NEWthang.find({}, { "FieldxExp" : { $slice: [0,1]} } ).pretty()
{
"_id" : ObjectId("516c4053baa133464d36e836"),
"FieldxExp" : [
{
"Doc1 K1" : "Val A1",
"Doc1 K2" : "Val A2",
"Doc1 K3" : "Val A3"
}
]
}
Finally, how about write the Query in some PHP ::
// these will be for building the MongoCursor:
$myEmptyArray = array();
$TheProjectionCriteria = array('FieldxExp'=> array('$slice' => array(1,1)));
// which gets set up here:
$CursorNEWthang1 = new MongoCollection($db, 'NEWthang');
// and now ready to make the Query/read:
$ReadomgomgPls=$CursorNEWthang1->find($myEmptyArray,$TheProjectionCriteria);
and the second document will be printed out:
foreach ($ReadomgomgPls as $somekey=>$AxMongoDBxDocFromCollection) {
var_dump($AxMongoDBxDocFromCollection);echo '<br />';
}
Hope this is helpful for a few folks.