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": {} })
Related
I have a MongoDB question. I have a search in an aggregation with $match.
Search should check an array if one of the values matches a value of the array inside the documents.
As an example:
var stringList = 'general,online,offline'; //--> should check each value of this list
and two documents as an example
{
"_id" : ObjectId("5e8f3a64ec717a0013d2f1f9"),
"category" : [
"general",
"online",
"internal",
"miscellaneous"
]},
{
"_id" : ObjectId("5e8f3afeec717a0013d2f1fa"),
"category" : [
"offline"
]
}
I´ve tried a lot but I don´t found out how it is possible to check each value of the string list with each value in the category array. My example should show both documents, but if I use $in I don´t get any result.
What I tried is:
Split the list by comma and map
use of $elemMatch
use if $in
use combination of $elemMatch and $in
I hope I could explain my problem with my aggregation.
Thx everyone for his help.
You should be able to split the string on , with .split function, then pass this in to a $in query.
var stringList = 'general,online,offline';
db.documents.find( { "category" : { $in : stringList.split(",") } } );
{ "_id" : ObjectId("5e8f3a64ec717a0013d2f1f9"), "category" : [ "general", "online", "internal", "miscellaneous" ] }
{ "_id" : ObjectId("5e8f3afeec717a0013d2f1fa"), "category" : [ "offline" ] }
You can also do this in a $match in an aggregation query.
> db.documents.aggregate([
{ $match : { category: { $in : stringList.split(",") } }}
])
Here is an example, where we can search the array name from by using the regex method in the query.
var x = ["sai","test","jacob","justin"],
regex = x.join("|");
db.documents.find({
"firstName": {
"$regex": regex,
"$options": "i"
}
});
So heres my mongodb document:
{
"_id" : "",
"lists" : [
{
"name" : "list 1",
"items" : []
},
{
"name" : "list 2",
"items" : []
}
]
}
How would I go about adding an object inside "items"?
This is the code I have so far, but it doesn't work:
xxx.update(_id, {$push: { "lists.$.items": item}});
Note that I have access to the index (variable called 'index'), so its possible to insert an item at index, 0, 1, 2..., etc.
I tried this before, but it won't work:
xxx.update({_id, "lists": index}, {$push: { "lists.$.items": item}});
I also looked at other similar questions and couldn't find anything. Most of them have some sort of id field in their arrays, but I don't.
What about
xxx.update({_id}, {$push: { "lists.index.items": item}});
Of course this would fail, what I mean is replace index with real index values
xxx.update({_id}, {$push: { "lists.2.items": item}});
You can manipulate the update json based on the index maybe as below.
var update = '{$push: { "lists.'+index+'.items": '+item+'}}';
var updateObj = JSON.parse(update);
xxx.update({_id}, updateObj);
Not sure if it will work as it is or it would need further tweaking, but you get the idea.
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 } });
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'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.