Given a MongoDB collection with the following document structure:
{
array_of_subdocs:
[
{
animal: "cat",
count: 10
},
{
animal: "dog",
count: 20
},
...
]
}
where each document contains an array of sub-documents, I want transform the collection into documents of the structure:
{
cat: { count: 10 },
dog: { count: 20 },
...
}
where each sub-document is now the value of a new field in the main document named after one of the values within the sub-document (in the example, the values of the animal field is used to create the name of the new fields, i.e. cat and dog).
I know how to do this with eval with a Javascript snippet. It's slow. My question is: how can this be done using the aggregation pipeline?
According to this feature request and its solution, the new feature will be added for this functionality - Function called arrayToObject.
db.foo.aggregate([
{$project: {
array_of_subdocs: {
$arrayToObject: {
$map: {
input: "$array_of_subdocs",
as: "pair",
in: ["$$pair.animal", "$$pair.count"]
}
}
}
}}
])
But at the moment, no solution. I suggest you to change your data structure. As far as I see there are many feature requests labeled as Major but not done for years.
Related
In some documents I have a property with a complex structure like:
{
content: {
foo: {
id: 1,
name: 'First',
active: true
},
bar: {
id: 2,
name: 'Second',
active: false
},
baz: {
id: 3,
name: 'Third',
active: true
},
}
I'm trying to make a query that can find all documents with a given value in the field name across the different second level objects foo, bar, baz
I guess that a solution could be:
db.getCollection('mycollection').find({ $or: [
{'content.foo.name': 'First'},
{'content.bar.name': 'First'},
{'content.baz.name': 'First'}
]})
But a I want to do it dynamic, with no need to specify key names of nested fields, nether repeat the value to find in every line.
If some Regexp on field name were available , a solution could be:
db.getCollection('mycollection').find({'content.*.name': 'First'}) // Match
db.getCollection('mycollection').find({'content.*.name': 'Third'}) // Match
db.getCollection('mycollection').find({'content.*.name': 'Fourth'}) // Doesn't match
Is there any way to do it?
I would say this is a bad schema if you don't know your keys in advance. Personally I'd recommend to change this to an array structure.
Regardless what you can do is use the aggregation $objectToArray operator, then query that newly created object. Mind you this approach requires a collection scan each time you execute a query.
db.collection.aggregate([
{
$addFields: {
arr: {
"$objectToArray": "$content"
}
}
},
{
$match: {
"arr.v.name": "First"
}
},
{
$project: {
arr: 0
}
}
])
Mongo Playground
Another hacky approach you can take is potentially creating a wildcard text index and then you could execute a $text query to search for the name, obviously this comes with the text index/query limitations and might not be right for your usecase.
I've two mongo collections - File and Folder.
Both have some common fields like name, createdAt etc. I've a resources API that returns a response having items from both collections, with a type property added. type can be file or folder
I want to support pagination and sorting in this list, for example sort by createdAt. Is it possible with aggregation, and how?
Moving them to a container collection is not a preferred option, as then I have to maintain the container collection on each create/update/delete on either of the collection.
I'm using mongoose too, if it has got any utility function for this, or a plugin.
In this case, you can use $unionWith. Something like:
Folder.aggregate([
{ $project: { name: 1, createdAt: 1 } },
{
$unionWith: {
coll: "files", pipeline: [ { $project: { name: 1, createdAt: 1 } } ]
}
},
... // your sorting go here
])
I am fairly new to MongoDB and cant seem to find a solution to this problem.
I have a database of documents that has this structure:
{
id: 1
elements: [ {elementId: 1, nr1: 1, nr2: 3}, {elementId:2, nr1:5, nr2: 10} ]
}
I am looking for a query that can add a value nr3 which is for example nr2/nr1 to all the objects in the elements array, so that the resulting document would look like this:
{
id: 1
elements: [ {elementId: 1, nr1: 1, nr2: 3, nr3:3}, {elementId:2, nr1:5, nr2: 10, nr3: 2} ]
}
So I imagine a query along the lines of this:
db.collection.updateOne({id:1}, {$set:{"elements.$[].nr3": nr2/nr1}})
But I cant find how to get the value of nr2 and nr1 of the same object in the array.
I found some similar questions on stackoverflow stating this is not possible, but they were 5+ years old, so I thought maybe they have added support for something like this.
I realize I can achieve this with first querying the document and iterate over the elements-array doing updates along the way, but for the purpose of learning I would love to see if its possible to do this in one query.
You can use update with aggregation pipeline starting from MongoDB v4.2,
$map to iterate loop of elements
divide nr2 with nr1 using $divide
merge current object and new field nr3 using $mergeObjects
db.collection.updateOne(
{ id: 1 },
[{
$set: {
elements: {
$map: {
input: "$elements",
in: {
$mergeObjects: [
"$$this",
{ nr3: { $divide: ["$$this.nr2", "$$this.nr1"] } }
]
}
}
}
}
}]
)
Playground
db.collection.update(
{ id:1},
{ "$set": { "elements.$[elem].nr3":elements.$[elem].nr2/elements.$[elem].nr1} },
{ "multi": true }
);
I guess this should work
I have a short but important question. I am new to MongoDB and querying.
My database looks like the following: I only have one document stored in my database (sorry for blurring).
The document consists of different fields:
two are blurred and not important
datum -> date
instance -> Array with an Embedded Document Object; Our instance has an id, two not important fields and a code.
Now I want to query how many times an object in my instance array has the group "a" and a text "sample"?
Is this even possible?
I only found methods to count how many documents have something...
I am using Mongo Compass, but i can also use Pymongo, Mongoengine or every other different tool for querying the mongodb.
Thank you in advance and if you have more questions please leave a comment!
You can try this
db.collection.aggregate([
{
$unwind: "$instance"
},
{
$unwind: "$instance.label"
},
{
$match: {
"instance.label.group": "a",
"instance.label.text": "sample",
}
},
{
$group: {
_id: {
group: "$instance.label.group",
text: "$instance.label.text"
},
count: {
$sum: 1
}
}
}
])
Below I have a structure for supporting custom picklist fields (in this example) within my sails.js application. The general idea is we support a collection of custom picklist values on any model within the app and the customer can have total control of the configuration of the custom field.
I went with this relationship model as using a simple json field lacks robustness when it comes to updating each individual custom picklist value. If I allow a customer to change "Internal" to "External" I need to update all records that have the value "Internal" recorded against that custom picklist with the new value.
This way - when I update the "value" field of CustomPicklistValue wherever that record is referenced via ID it will use the new value.
Now the problem comes when I need to integrate this model into my existing report engine...
rawCollection
.aggregate(
[
{
$match: {
createdAt: {
$gte: rangeEndDate,
$lte: rangeStartDate
},
...$match
}
},
{
$project: {
...$project,
total: $projectAggregation
}
},
{
$group: {
_id: {
...$groupKey
},
total: {
[`$${aggrAttrFunc}`]: "$total"
}
}
}
],
{
cursor: {
batchSize: 100
}
}
)
Here is the main part of a method for retrieving and aggregating any models stored in my mongodb instance. A user can specify a whole range of things including but not limited to the model, field specific date ranges and filters such as "where certificate status equals expired" etc.
So I'm now presented with this data structure:
{
id: '5e5fb732a9422a001146509f',
customPicklistValues: [
{
id: '5e4e904f16ab94bff1a324a0',
value: 'Internal',
fieldName: 'Business Group',
customPicklist: '109c7a1a9d00b664f2ee7827'
},
{
id: '5e4e904f16ab94bff1a324a4',
value: 'Slack',
fieldName: 'Application',
customPicklist: '109c5a1a9d00b664f2ee7827'
}
],
}
And for the life of me can't work out if there's any way I can essentially pull out fieldName and value for each of the populated records as key-value pairs and add each to the parent record before running my match clause...
I think I need to use lookup to initially populate the customPicklistValues and then merge them somehow?
Any help appreciated.
EDIT:
#whoami has suggested I use $addFields. There was a fair amount I needed to do before $addFields to populate the linked records (due to how Waterline via sails.js handles saving Mongo ObjectIDs in related collections as strings), you can see my steps in compass here:
Final step would be to edit this or add a stage to it to actually be able to support a key:value pair like Business Group: "Finance" in this example.
You can try these stages after your $lookup stage :
db.collection.aggregate([
{
$addFields: {
customPicklistValues:
{
$arrayToObject: {
$map: {
input: '$customPicklistValues',
in: { k: '$$this.fieldName', v: '$$this.value' }
}
}
}
}
},
{ $replaceRoot: { newRoot: { $mergeObjects: ['$customPicklistValues', '$$ROOT'] } } },
{ $project: { customPicklistValues: 0 } }
])
Test : MongoDB-Playground