MongoDB seems to interpret $set paths with numerical components as object keys rather than array indexes if the field has not already been created as an array.
> db.test.insert({_id: "one"});
> db.test.update({_id: "one"}, {$set: {"array.0.value": "cheese"}});
> db.find({_id: "one"})
{ "_id": "one", "array": { "0" : { "value" : "cheese" } }
I expected to get "array": [{"value": "cheese"}], but instead it was initialized as an object with a key with the string "0".
I could get an array by initializing the whole array, like so:
> db.test.update({_id: "one"}, {$set: {"array": [{"value": "cheese"}]}});
... but this would clobber any existing properties and other array elements that might have been previously set.
Is there any way to convince $set that I want "array" to be an array type, with the following constraints:
I want to execute this in a single query, without looking up the record first.
I want to preserve any existing array entries and object values
In short, I want the behavior of $set: {"array.0.value": ... } if "array" had already been initialized as an array, without knowing whether or not it has. Is this possible?
I am not sure if this is possible without lookup. Perhaps you can change schema design, and try something like this:
db.test.insert({_id: "one"});
db.test.update({_id: "one"}, {$addToSet: {array: { $each:['cheese', 'ham'] }}});
db.test.findOne({_id:'one'});
// { "_id" : "one", "array" : [ "cheese", "ham" ] }
Handling array elements (sub-documents in array) in MongoDb is pain. https://jira.mongodb.org/browse/SERVER-1243
Related
Consider the following MongoDB collection of a few thousand Objects:
{
_id: ObjectId("xxx")
FM_ID: "123"
Meter_Readings: Array
0: Object
Date: 2011-10-07
Begin_Read: true
Reading: 652
1: Object
Date: 2018-10-01
Begin_Reading: true
Reading: 851
}
The wrong key was entered for 2018 into the array and needs to be renamed to "Begin_Read". I have a list using another aggregate of all the objects that have the incorrect key. The objects within the array don't have an _id value, so are hard to select. I was thinking I could iterate through the collection and find the array index of the errored Readings and using the _id of the object to perform the $rename on the key.
I am trying to get the index of the array, but cannot seem to select it correctly. The following aggregate is what I have:
[
{
'$match': {
'_id': ObjectId('xxx')
}
}, {
'$project': {
'index': {
'$indexOfArray': [
'$Meter_Readings', {
'$eq': [
'$Meter_Readings.Begin_Reading', True
]
}
]
}
}
}
]
Its result is always -1 which I think means my expression must be wrong as the expected result would be 1.
I'm using Python for this script (can use javascript as well), if there is a better way to do this (maybe a filter?), I'm open to alternatives, just what I've come up with.
I fixed this myself. I was close with the aggregate but needed to look at a different field for some reason that one did not work:
{
'$project': {
'index': {
'$indexOfArray': [
'$Meter_Readings.Water_Year', 2018
]
}
}
}
What I did learn was the to find an object within an array you can just reference it in the array identifier in the $indexOfArray method. I hope that might help someone else.
I have two collections in Mongo. For simplification I´m providing a minified example
Template Collection:
{
templateId:0,
values:[
{data:"a"},
{data:"b"},
{data:"c"}
{data:"e"}
]
}
Data Collection:
{
dataId:0,
templateId:0,
values:[
{data:"a",
value: 10},
{data:"b",
value: 120},
{data:"c",
value: 3220},
{data:"d",
value: 0}
]
}
I want to make a sync from Template Collection -> Data Collection, between the template 0 and all documents using that template. In the case of the example, that would mean:
Copy {data:"e"} into the arrays of all documents with the templateId: 0
Remove {data:"d"} from the arrays of all documents with the templateId: 0
BUT do not touch the rest of the items. I can´t simply replace the array, because those values have to be kept
I´ve found a solution for 1.
db.getCollection('data').update({templateId:0},
{$addToSet: {values: {
$each:[
{data:"a"},
{data:"b"},
{data:"c"}
{data:"e"}
]
}}}, {
multi: true}
)
And a partial solution for 2.
I got it. First tried with $pullAll, but the normal $pull seems to work together with the $nin operator
db.getCollection('data').update({templateId:"QNXC4bPAF9J6r9FQu"},
{$pull:{values: { $nin:[
{data:"a"},
{data:"b"},
{data:"c"}
{data:"e"}]
}}}, {
multi: true}
)
This will remove {data:"d"} from all document arrays, but it seems to overwrite the complete array, and this is not what I want, as those value entries need to be persisted
But how can I perform a query like Remove everything from an array EXCEPT/NOT IN [a,b,c,d,...] ?
I have this collection :
{
username : "user1",
arr : [
{
name : "test1",
times : 0
},
{
name : "test2",
times : 5
}
]
}
I have an array with some object. This objects have a name and the value times. Now I want to add new objects, if my array doesn't contain them. Example:
I have this two objects with the name "test1" and "test2" already in the collection. I want now to insert the objects "test2", "test3" and "test4". It should only add the object "test3" and "test4" to the array and not "test2" again. The value times doesn't do anything in this case, they should just have the value 0 when it gets insert.
Is there a way to do this with one query?
If you can insert test1, test2,... one by one, then you can do something like this.
db.collection.update(
{username : "user1", 'arr.name': {$ne: 'test2'}},
{$push: {
arr: {'name': 'test2', 'times': 0}
}
})
The $ne condition will prevent the update if the name is already present in arr.
You can now use the addToSet operator that is built just for that: adds a value to an array if it does not exist.
Documentation: https://docs.mongodb.com/manual/reference/operator/update/addToSet/
My document structure is as below.
{
"_id" : {
"timestamp" : ISODate("2016-08-27T06:00:00.000+05:30"),
"category" : "marketing"
},
"leveldata" : [
{
"level" : "manager",
"volume" : [
"45",
"145",
"2145"
]
},
{
"level" : "engineer",
"volume" : [
"2145"
]
}
]
}
"leveldata.volume" embedded array document field can have around 60 elements in it.
In this case, "leveldata" is an array document.
And "volume" is another array field inside "leveldata".
We have a requirement to fetch specific elements from the "volume" array field.
For example, elements from specific positions, For Example, position 1-5 within the array element "volume".
Also, we have used positional operator to fetch the specific array element in this case based on "leveldata.level" field.
I tried using the $slice operator. But, it seems to work only with arrays not with array inside array fields, as that
is the case in my scenario.
We can do it from the application layer, but that would mean loading the entire the array element from mongo db to memory and
then fetching the desired elements. We want to avoid doing that and fetch it directly from mongodb.
The below query is what I had used to fetch the elements as required.
db.getCollection('mycollection').find(
{
"_id" : {
"timestamp" : ISODate("2016-08-26T18:00:00.000-06:30"),
"category" : "sales"
}
,
"leveldata.level":"manager"
},
{
"leveldata.$.volume": { $slice: [ 1, 5 ] }
}
)
Can you please let us know your suggestions on how to address this issue.
Thanks,
mongouser
Well yes you can use $slice to get that data like
db.getCollection('mycollection').find({"leveldata.level":"manager"} , { "leveldata.volume" : { $slice : [3 , 1] } } )
I'd like to be able to query documents where an array attribute is either null or of zero length. I've tried using $or, like
{ things : { $or : [null, { $size : 0 } ] } }
but MongoDB complains about it:
{ "$err" : "invalid operator: $or", "code" : 10068 }
It appears that MongoDB doesn't want to use $and or $or on array attributes. I thought that simply querying for { things : { $size : 0 } } would return documents that had non-null arrays of zero length as well as null arrays, but that doesn't appear to be true.
How can I issue a query to find all documents where an array attribute is null or of zero length?
You can also do this with $in:
db.test.find({things: {$in: [null, []]}})
That will also include docs with things: [null].
Another way is to use $exists on the first element of the things array:
db.test.find({'things.0': {$exists: false}})
That will find the docs where things does not have at least one element. In contrast with the above, it will still include docs with things: null or things: [], but not things: [null].
When things is null, it is not of type Array. It is of type Null which is its own data-type. $size only matches arrays. Any document where the field is something different than an array will never be matched by it.
Your syntax error is in how you use the $or operator. You don't use it for a field, you use it as a field.
db.collection.find({
$or: [
{ things: { $size: 0 } }, // 0-elements array
{ things: null } // field which is null
]
});