I am struggling with some query in MongoDB. Let's say I have standings collection which looks like
{
"competitions: {id: "1", name:"someLeague"},
"standings": [
{
"type": "TOTAL",
"table": [
{
"position": "1",
"team": {
"id": "123",
"name": "XYZ"
},
won: "1",
draw: "2",
lost: "3",
points: "4",
},
{
"position": "2",
"team": {
"id": "321",
"name": "ABC"
}
...
And the fixtures collection which looks like
{
matchDay: "YYYY-MM-DD",
homeTeam: {id: "123", name:"ABC"},
awayTeam: {id: "321", name:"XYZ"},
}
Is it possible to connect this two collection this way that field "homeTeam" in fixtures collection will contain all information including points, won games etc. from standings where type would be total? And same thing with the field awayTeam, with the proviso that information of team would be from array where standings type is away.
There is no means in MongoDB to reference a document of collection A in collection B so that find queries on collection B automatically provide attributes of the referenced document. However, as of MongoDB 3.2 it is possible to use $lookup command as part of an aggregation (see https://stackoverflow.com/a/33511166/3976662) to JOIN (similar to standard SQL) over multiple collections during the query. In your case, you can consider using $lookup in conjunction with $unwind - similar to the example in the MongoDB docs. Spring Data Mongo supports $lookup since 1.10.
Related
I am trying to extract some data from a legacy mongo db (v. 2.0.4). I have data that is structured like this:
{"_id": "1",
"#graph": {"ma:isMemberOf": [{"#id": "524224b804743b02a4c23488",
"title": "IHum 350",
"transcript": "False"},
{"#id": "53cfd59404743bc3c9119adf",
"restrictor": "578e89ae04743b7b0816beff",
"title": "Spanish 339",
"transcript": "False"}],
"ma:title": "Toy title 1"},
"_id": "2",
"#graph": {"ma:isMemberOf": [{"#id": "524224b804743b02a4c23488",
"title": "IHum 350",
"transcript": "False"}],
"ma:title": "Toy title 2"}}
...and I want to write a query that will find all of the documents that are members of a particular group (matching the #id field). For example, I want to be able to search for 524224b804743b02a4c23488 and receive documents 1 and 2. Or to search for 53cfd59404743bc3c9119adf and receive only document 1.
I have tried several things, but I can't figure out how to query embedded objects.
db.collection.find({
"#graph.ma:isMemberOf.#id": <your query>
})
Here is the Mongo playground for your reference.
I have two collections with same structure and want to merge them in aggregation result and query & sort over them after merging.
E.g.;
First collection:
{_id: "123", "name": "sercan"}
Second collection:
{_id: "456", "name": "hakan"}
What I want;
[{_id: "123", "name": "sercan"}, {_id: "456", "name": "hakan"}]
What I tried;
{"from":"secondCollection",pipeline: [],"as":"seconds"}
// result
{_id: "123", "name": "sercan", seconds: [{_id: "456", "name": "hakan"}]}
And the above trial, puts all documents into seconds if there're more documents in the second collection.
Thanks in advance
The one option I have used is $merge in MongoDB.
It's basically merge one collection to another and create new output collection if it does not exist.
Reference:
https://www.mongodb.com/docs/manual/reference/operator/aggregation/merge/
I've written Users, Clubs and Followers collections for the sake of an example the below.
I want to find all user documents from the Users collection that are following "A famous club". How can I find those? and Which way is the fastest?
More info about 'what do I want to do - Edge collections'
Users collection
{
"_id": "1",
"fullname": "Jared",
"country": "USA"
}
Clubs collection
{
"_id": "12",
"name": "A famous club"
}
Followers collection
{
"_id": "159",
"user_id": "1",
"club_id": "12"
}
PS: I can get the documents using Mongoose like the below way. However, creating followers array takes about 8 seconds with 150.000 records. And second find query -which is queried using followers array- takes about 40 seconds. Is it normal?
Clubs.find(
{ club_id: "12" },
'-_id user_id', // select only one field to better perf.
function(err, docs){
var followers = [];
docs.forEach(function(item){
followers.push(item.user_id)
})
Users.find(
{ _id:{ $in: followers } },
function(error, users) {
console.log(users) // RESULTS
})
})
There is no an eligible formula to manipulate join many-to-many relation on MongoDB. So I combined collections as embedded documents like the below. But the most important taks in this case creating indexes. For instance if you want to query by followingClubs you should create an index like schema.index({ 'followingClubs._id':1 }) using Mongoose. And if you want to query country and followingClubs you should create another index like schema.index({ 'country':1, 'followingClubs._id':1 })
Pay attention when working with Embedded Documents: http://askasya.com/post/largeembeddedarrays
Then you can get your documents fastly. I've tried to get count of 150.000 records using this way it took only 1 second. It's enough for me...
ps: we musn't forget that in my tests my Users collection has never experienced any data fragmentation. Therefore my queries may demonstrated good performance. Especially, followingClubs array of embedded documents.
Users collection
{
"_id": "1",
"fullname": "Jared",
"country": "USA",
"followingClubs": [ {"_id": "12"} ]
}
Clubs collection
{
"_id": "12",
"name": "A famous club"
}
Is it possible to query mongodb to return array of matching document id values, without the related keys?
Please consider following 'parent' data structur:
{
"_id": ObjectId("52448e4697fb2b775cb5c3a7"),
"name": "Peter",
"children": [
{
"name": "joe"
}
]
},
{
"_id": ObjectId("52448e4697fb2b775cb5c3b6"),
"name": "Marry",
"children": [
{
"name": "joe"
}
]
}
I would to query for an array of parent _ids whose children have the name "joe"
For provided sample data, I would like the following output returned from mongo:
[ObjectId("52448e4697fb2b775cb5c3a7"), ObjectId("52448e4697fb2b775cb5c3b6")]
I know that I can query for an output like this, which also contains the keys
[{"_id": ObjectId("52448e4697fb2b775cb5c3a7")}, {"_id": ObjectId("52448e4697fb2b775cb5c3b6")}]
However I need to push above array to another document with an update operation like this:
db.statistic.update({"date": today}, {$push: {"children": [ObjectId("52448e4697fb2b775cb5c3a7"), ObjectId("52448e4697fb2b775cb5c3b6")]}}, true, false)
I would like to avoid sorting out the document structure, in case it is possible to just return an array containing the appropriate values using mongo
It should be possible by
db.coll.distinct("_id", {"children.name": "joe"})
To clarify: I have a document with a subdoc. I create a new document with the same data of the other one and it gets a new id. However, when I copy the subdoc array they do not get a new id.
Are subdocs id local to the parent doc? I.e. would the following be a problem?
[
{
"__v": 1,
"_id": "5214af03a9f53efa61000004",
"name": "Foo",
"subdocs": [
{
"thing": "value",
"_id": "5214af03a9f53efa61000006"
}
]
},
{
"__v": 0,
"name": "Foo",
"_id": "5214af03a9f53efa61000014",
"subdocs": [
{
"thing": "value",
"_id": "5214af03a9f53efa61000006"
}
]
}
]
There is a unique index on the _id field of documents stored directly in a collection, but not for embedded documents, nor is there any requirement that embedded documents have an _id field at all. The two documents you have provided are both valid to be stored in MongoDB in the same database (I'm interpreting your example as an array of two documents that are both stored directly in a collection together).