Here is a MongoDB query and aggregation puzzle. Fist some sample records:
# Document 1
{
items: [
{
type: "X",
id: 123
},
{
type: "Y",
id: 456
}
]
}
# Document 2
{
items: [
{
type: "A",
id: 789
},
{
type: "B",
id: 321
}
]
}
# Document 3
{
items: [
{
type: "P",
id: 987
},
{
type: "X",
id: 654
}
]
}
# Document 4
{
items: [
{
type: "Q",
id: 246
},
{
type: "X",
id: 654
}
]
}
My goal is to find all the distinct id values for documents which contain a type: X where the id is the id associated with the type: X element.
For example, in the above, what I would like my result to be is:
[ 123, 654 ]
These are the unique values of the id field associated with the type: X.
You can start with unwinding your items. Then you can filter out by type. In last step you can utilize $addToSet operator which will eliminate duplicates.
db.collection.aggregate([
{ $unwind: "$items" },
{ $match: { "items.type": "X" } },
{
$group: {
_id: 1,
ids: { $addToSet: "$items.id" }
}
}
])
Grouping with _id: 1 means that I'm grouping by whatever: I know that everything should be a part of only one group, but I need to use $addToSet.
You can use below aggregation to get unique ids.
Query $filters the items where type is input type followed by $arrayElemAt to project matching item and $let to extract the id field.
$group all the items with $addToSet id values to output the unique values.
db.collection_name.aggregate([{"$group":{
"_id":null,
"ids":{
"$addToSet":{
"$let":{
"vars":{
"obj":{
"$arrayElemAt":[
{"$filter":{
"input":"$items",
"cond":{"$eq":["$$this.type","X"]}
}},
0
]
}
},
"in":"$$obj.id"
}
}
}
}}])
Related
I have the following sample of data:
{
_id: 1,
seniorityDate: '2001-01-01T00:00:00Z',
assigned: [
{
groupId: 11,
system: 'Dep',
effectiveDate: null
},
{
groupId: 12,
system: 'Team',
effectiveDate: null
},
...
]
}
and I would like to update the object effectiveDate based on seniorityDate in the array of assigned where system:'Team' only:
db.collection.updateMany({},
[{
$set: {
'assigned.$[elem].effectiveDate': '$seniorityDate'
}
}], {
arrayFilters: [{
"elem.system": "Team"
}]
})
but I got the following error:
arrayFilters may not be specified for pipeline-syle updates
The expected result will be:
{
_id: 1,
seniorityDate: '2001-01-01T00:00:00Z',
assigned: [
{
groupId: 11,
system: 'Dep',
effectiveDate: null
},
{
groupId: 12,
system: 'Team',
effectiveDate: '2001-01-01T00:00:00Z'
},
...
]
}
How can I achieve it?
You can't use the arrayFilters with the aggregation pipeline at the same time. While you are updating the value from another field, hence you can only achieve with aggregation pipeline.
$set - Set assigned field.
1.1. $map - Iterate element in assigned array and return new array.
1.1.1. $mergeObjects - Merge current iterated document with the document from 1.1.1.1.
1.1.1.1. Document with effectiveDate field. With the $cond operator, if matches the condition, use the seniorityDate value, else remain the existing value.
db.collection.updateMany({},
[
{
$set: {
"assigned": {
$map: {
input: "$assigned",
in: {
$mergeObjects: [
"$$this",
{
effectiveDate: {
$cond: {
if: {
$eq: [
"$$this.system",
"Team"
]
},
then: "$seniorityDate",
else: "$$this.effectiveDate"
}
}
}
]
}
}
}
}
}
])
Thanks to #rickhg12hs' suggestion, always limit the document for better performance, as you know which document/field should be updated by condition.
Hence your update query with query condition will be as below:
db.collection.updateMany({
"assigned.system": "Team"
},
[
...
])
Demo # Mongo Playground
I have an issue that need to insert index number when get data. First i have this data for example:
[
{
_id : 616efd7e56c9530018e318ac
student : {
name: "Alpha"
email: null
nisn: "0408210001"
gender : "female"
}
},
{
_id : 616efd7e56c9530018e318af
student : {
name: "Beta"
email: null
nisn: "0408210001"
gender : "male"
}
}
]
and then i need the output like this one:
[
{
no:1,
id:616efd7e56c9530018e318ac,
name: "Alpha",
nisn: "0408210001"
},
{
no:2,
id:616efd7e56c9530018e318ac,
name: "Beta",
nisn: "0408210002"
}
]
i have tried this code but almost get what i expected.
{
'$project': {
'_id': 0,
'id': '$_id',
'name': '$student.name',
'nisn': '$student.nisn'
}
}
but still confuse how to add the number of index. Is it available to do it in $project or i have to do it other way? Thank you for the effort to answer.
You can use $unwind which can return an index, like this:
db.collection.aggregate([
{
$group: {
_id: 0,
data: {
$push: {
_id: "$_id",
student: "$student"
}
}
}
},
{
$unwind: {path: "$data", includeArrayIndex: "no"}
},
{
"$project": {
"_id": 0,
"id": "$data._id",
"name": "$data.student.name",
"nisn": "$data.student.nisn",
"no": {"$add": ["$no", 1] }
}
}
])
You can see it works here .
I strongly suggest to use a $match step before these steps, otherwise you will group your entire collection into one document.
You need to run a pipeline with a $setWindowFields stage that allows you to add a new field which returns the position of a document (known as the document number) within a partition. The position number creation is made possible by the $documentNumber operator only available in the $setWindowFields stage.
The partition could be an extra field (which is constant) that can act as the window partition.
The final stage in the pipeline is the $replaceWith step which will promote the student embedded document to the top-level as well as replacing all input documents with the specified document.
Running the following aggregation will yield the desired results:
db.collection.aggregate([
{ $addFields: { _partition: 'students' }},
{ $setWindowFields: {
partitionBy: '$_partition',
sortBy: { _id: -1 },
output: { no: { $documentNumber: {} } }
} },
{ $replaceWith: {
$mergeObjects: [
{ id: '$_id', no: '$no' },
'$student'
]
} }
])
Suppose I want to sort the data based on the current city first and then the remaining country data. Is there any way I achieve that in MongoDB?
Example
[
{ id: 2, name: 'sdf' },
{ id: 3, name: 'sfs' },
{ id: 3, name: 'aaa' },
{ id: 1, name: 'dsd' },
];
What I want as an outcome is the data with id 3 at first and the remaining other.
like
[
{ id: 3, name: 'sfs' },
{ id: 3, name: 'aaa' },
{ id: 1, name: 'dsd' },
{ id: 2, name: 'sdf' },
];
It's just a example,
My actual requirement is to sort the data based on certain category first and then the remaining one
It's not possible within mongodb but you could first fetch the documents from the db and then sort them in Javascript (or whatever other language you're using to present the data).
On a side note, having duplicate values in the "id" field is not a good practice and defies the definition of id itself.
There is no straight way to sort condationaly in MongoDB, as per your example you can try aggregation query,
$facet to separate result for both types of documents
first, to get id: 3 documents
second, to get id is not 3 documents and sort by id in ascending order
$project and $concatArrays to concat both arrays in siquance
$unwind deconstruct all array
$replaceRoot to replace all object to root
db.collection.aggregate([
{
$facet: {
first: [
{ $match: { id: 3 } }
],
second: [
{ $match: { id: { $ne: 3 } } },
{ $sort: { id: 1 } }
]
}
},
{
$project: {
all: { $concatArrays: ["$first", "$second"] }
}
},
{ $unwind: "$all" },
{ $replaceRoot: { newRoot: "$all" } }
])
Playground
In mongo I have a documents that follow the below pattern :
{
name: "test",
codes: [
[
{
code: "abc",
value: 123
},
{
code: "def",
value: 456
},
],
[
{
code: "ghi",
value: 789
},
{
code: "jkl",
value: 012
},
]
]
}
I'm using an aggregate query (because of joins) and in a $project block I need to return the "name" and the value of the object that has a code of "def" if it exists and an empty string if it doesn't.
I can't simply $unwind codes and $match because the "def" code is not guaranteed to be there.
$filter seems like the right approach as $elemMatch doesn't work, but its not obvious to me how to do this on nested array of arrays.
You can try below query, instead of unwinds & filter this can give you required result with less docs to operate on :
db.collection.aggregate([
/** merge all arrays inside codes array into code array */
{
$addFields: {
codes: {
$reduce: {
input: '$codes',
initialValue: [],
in: { $concatArrays: ["$$value", "$$this"] }
}
}
}
},
/** project only needed fields & value will be either def value or '',
* if 'def' exists in any doc then we're check index of it to get value of that particular object using arrayElemAt */
{
$project: {
_id:0, name: 1, value:
{
$cond: [{ $in: ["def", '$codes.code'] }, { $arrayElemAt: ['$codes.value', { $indexOfArray: ["$codes.code", 'def'] }] }, '']
}
}
}])
Test : MongoDB-Playground
is it possible in MongoDB to find some objects that match a query and then to modify the result without modifying the persistent data?
For example, let
students = [
{ name: "Alice", age: 25 },
{ name: "Bob", age: 22 },
{ name: "Carol", age: 19 },
{ name: "Dave", age: 18}
]
Now, I want to query all students that are younger than 20 and in the search result, I just want to replace "age: X" with "under20: 1" resulting in the following:
result = [
{ name: "Carol", under20: 1 },
{ name: "Dave", under20: 1}
]
without changing anything in the database.
Sure, it is possible to get the result and then call a forEach on it, but that sounds so inefficient because I have to rerun every object again, so I'm searching for an alternative. Or is there no one?
A possible solution would be to use an aggregation pipline with a $match followed by a $project:
db.students.aggregate(
[
{
$match: { age: { $lt: 20 } }
},
{
$project:
{
_id: false,
name: true,
under20: { $literal: 1 }
}
}
]);
The $literal: 1 is required as just using under20: 1 is the same as under20: true, requesting that field under20 be included in the result: which would fail as under20 does not exist in the document produced by the match.
Or to return all documents in students and conditionally generate the value for under20 a possible solution would be to use $cond:
db.students.aggregate(
[
{
$project:
{
_id: false,
name: true,
under20:
{
$cond: { if: { $lt: [ "$age", 20 ] }, then: 1, else: 0 }
}
}
}
]);