I have a "group" collection which groups documents from another "item" collection. The group collection is simply an array of ObjectId's from the item collection, however I want to make the objects in the group array more complex and still be able to use the $in and $nin operators.
How can I use $in when changing the value used with the $in operator to an object instead of only an ObjectId?
// current group document
{
_id: ObjectId(...),
items: [
ObjectId(...),
ObjectId(...)
]
}
// current item find query
db.item.find({ _id : { $in: group.items } }
I would like to change the group document to look like the following
{
_id: ObjectId(...),
items: [
{ _id : ObjectId(...), name: '...' },
{ _id : ObjectId(...), name: '...' }
]
}
Transform your group array to a simple array of ids to use for your find():
// revised item find logic
var itemGroupItemIds = group.items.map(function(item){
return item._id
});
db.item.find({ _id : { $in: itemGroupItemIds } });
Related
I need to get all documents that match an array of objects or an object with many fields.
Example 1 (array of objects)
If the document match the country_code than he must have one of postal_codes too
var locations = [
{
country_code : 'IT',
postal_codes : [21052, 21053, 21054, 21055]
},
{
country_code : 'GER',
postal_codes : [41052, 41053, 41054, 41055]
}
]
Example 2 (object with fields)
If the document match the key than it must have one of the values of that key
var location = {
'IT' : [21052, 21053, 21054, 21055],
'GER' : [41052, 41053, 41054, 41055]
}
I like the first type of document to match(array of objects) but how can i use to get all documents that match?
The documents to find have this structure:
{
"_id" : ObjectId("587f6f57ed6b9df409db7370"),
"description" : "Test description",
"address" : {
"postal_code" : "21052",
"country_code" : "IT"
}
}
You can use $in to find such collections.
db.collection_name.find(
{ address.postal_code: { $in: [your values] } },
)
Check this link for querying child objects.
Check this link for mongoDB $in
One way is to use the $or operator. This will help you limit the combinations of country_code and postal_code.
Your query should look something like this.
db.locations.find({
$or: [{
"country_code": "IT",
"postal_code": {
$in: [21052, 21053, 21054, 21055]
}
}, {
"country_code": "GER",
"postal_code": {
$in: [41052, 41053, 41054, 41055]
}
}]
})
I'm trying to find all users except for a few, like this:
// get special user IDs
var special = db.special.find({}, { _id: 1 }).toArray();
// get all users except for the special ones
var users = db.users.find({_id: {$nin: special}});
This doesn't work because the array that I'm passing to $nin is not and array of ObjectId but an array of { _id: ObjectId() }
Variable special looks like this after the first query:
[ { _id: ObjectId(###) }, { _id: ObjectId(###) } ]
But $nin in the second query needs this:
[ ObjectId(###), ObjectId(###) ]
How can I get just the ObjectId() in an array from the first query so that I can use them in the second query?
Or, is there a better way of achieving what I'm trying to do?
Use the cursor.map() method returned by the find() function to transform the list of { _id: ObjectId(###) } documents to an array of ObjectId's as in the following
var special = db.special.find({}, { _id: 1 }).map(function(doc){
return doc._id;
});
Another approach you can consider is using the $lookup operator in the aggregation framework to do a "left outer join" on the special collection and filtering the documents on the new "joined" array field. The filter should match on documents whose array field is empty.
The following example demonstrates this:
db.users.aggregate([
{
"$lookup": {
"from": "special",
"localField": "_id",
"foreignField": "_id",
"as": "specialUsers" // <-- this will produce an arry of "joined" docs
}
},
{ "$match": { "specialUsers.0": { "$exists": false } } } // <-- match on empty array
])
I have a document that looks like this:
{
"_id" : ObjectId("56fea43a571332cc97e06d9c"),
"sections" : [
{
"_id" : ObjectId("56fea43a571332cc97e06d9e"),
"registered" : [
"123",
"e3d65a4e-2552-4995-ac5a-3c5180258d87"
]
}
]
}
I'd like to remove the 'e3d65a4e-2552-4995-ac5a-3c5180258d87' in the registered array of only the specific section with the _id of '56fea43a571332cc97e06d9e'.
My current attempt is something like this, but it just returns the original document unmodified.
db.test.findOneAndUpdate(
{
$and: [
{'sections._id': ObjectId('56fea43a571332cc97e06d9e')},
{'sections.registered': 'e3d65a4e-2552-4995-ac5a-3c5180258d87'}
]
},
{
$pull: {
$and: [
{'sections._id': ObjectId('56fea43a571332cc97e06d9e')},
{'sections.registered': 'e3d65a4e-2552-4995-ac5a-3c5180258d87'}
]
}
})
I've looked in to $pull, but I can't seem to figure out how to make it work on an array of nested objects containing another array. The $pull examples all seem to deal with only one level of nesting. How do I remove the matching entry from the registered array of the item in the sections array with the _id that I supply?
You need to use the positional $ update operator to remove the element from your array. You need this is because "sections" is an array of sub-documents.
db.test.findOneAndUpdate(
{ "sections._id" : ObjectId("56fea43a571332cc97e06d9e") },
{ "$pull": { "sections.$.registered": "e3d65a4e-2552-4995-ac5a-3c5180258d87" } }
)
I have a MongoDB document containing an array where each element is supposed to have a non-empty _id. How do I identify array elements where the _id exists but is empty? I have some records like this:
{
"_id" : ObjectId("123456789012345678912345"),
"questions" : [
{
"_id" : {
},
...
},
...
]
}
The question itself has an empty _id. I've tried the following queries, which all return no results:
db.topics.find({ 'questions.$._id': {} })
db.topics.find({ 'questions.$._id': '' })
Sounds like you want to check for the presence of the value of the _id field in questions, so you could use the $in operator like so:
db.topics.find({"questions._id": { $in: [null, {}, ""] }})
That will find any record where _id is either null, empty object {} or empty string "".
You don't need the positional $ operator.
db.topics.find({ "questions._id": {} })
I'm trying to get a specific field from a subdocument array
I'm not gonna include any of the fields in the parent doc
Here is the sample document
{
"_id" : ObjectId("5409dd36b71997726532012d"),
"hierarchies" : [
{
"rank" : 1,
"_id" : ObjectId("5409df85b719977265320137"),
"name" : "CTO",
"userId" : [
ObjectId("53a47a639c52c9d83a2d71db")
]
}
]
}
I would like to return the rank of the hierarchy if the a userId is in the userId array
here's what I have so far in my query
collectionName.find({{hierarchies:
{$elemMatch : {userId: ObjectId("53a47a639c52c9d83a2d71db")}}}
, "hierarchies.$.rank", function(err,data){}
so far it returns the entire object in the hierarchies array I want, but I would like to limit it to just the rank property of the object.
The projection available to .find() queries generally in MongoDB does not do this sort of projection for internal elements of an array. All you can generally do is return the "matched" element of the array entirely.
For what you want, you use the aggregation framework instead, which gives you more control over matching and projection:
Model.aggregate([
{ "$match": {
"hierarchies.userId": ObjectId("53a47a639c52c9d83a2d71db")
}},
{ "$unwind": "$hierarchies" },
{ "$match": {
"hierarchies.userId": ObjectId("53a47a639c52c9d83a2d71db")
}},
{ "$project": {
"rank": "$hierarchies.rank"
}}
],function(err,result) {
})
That basically matches the documents, filters the array content of the document to just the match and then projects only the required field.