We are now using mongo-db to store data from tests. I am using Mongo-Shell
The document is structured like this:
{
static1:"abc",
static2:"xyz",
static3:"asd", [...],
nested:[
{
data1: "d1",
data2: "d2",
},
{
data1: "dx",
data4: "d4",
data5: "d5",
data6: "d6",
},
{
data1: "ds",
data8:"data8"
}, [...]
]
}
So the static-data is always in the same structure, but for every measurement the object can look different. It could be voltage with upper, lower and actual value. Or just comparison of a target value and an actual value. Highly dynamic.
Same data1-name represent same attributes.
Now e.g. I want to display only some static data and one (or several) attributes of a nested document.
I am using this query:
find({}, {_id:0, data1:1, "nested.data8":1}).pretty()
As expected, only the static-data1 is displayed, but the dynamic measurements has lots of empty objects in the shell-output
Example-Output:
{
"static1" : "123",
"nested" : [
{ },
{ },
{ }, [...] ,
{ "data8" : "OK" }
] }
The desired output would be:
{
"static1" : "123",
"nested" : [
{ "data8" : "d8" }
]
}
I also tried this query on the mongo shell:
aggregate( { $addFields: {"static":"$static1", "data8":"$nested.data8"} }, { $project:{"static1":1, "nested.data8":1} } ).pretty()
But the result is the same.
I hope there is a ways to get rid of the empty documents in the output.
Thanks
You can try $filter operator to filter result of nested array by checking condition not equal to empty object {}
db.collection.aggregate([
{
$project: {
_id: 0,
data1: 1,
"nested.data8": 1
}
},
{
$set: {
nested: {
$filter: {
input: "$nested",
cond: { $ne: ["$$this", {}] }
}
}
}
}
])
Playground
Related
I have a MongoDB Structure like this.
[
{
_id: 1,
data: [
{ price : "2", title: "title-1" }
]
},
{
_id: 2,
data: [
{ price : "2.0", title: "title-2" }
]
},
{
_id: 3,
data: [
{ price : "2.00", title: "title-3" },
{ price : "2.99", title: "title-4" }
]
}
I want to write a query where I can bring in all the titles which have a price value equal to 2(Number Type). But the issue is, the price field is of type String. And when I will query I have to put various conditions for price like:-
db.collection("test").find({ '$or': ["'data.price": '2'}, {"data.price": '2.0'}, {"data.price": '2.00'}] })
Is there a way in MongoDB where we can say that we want to convert a type before querying? OR Is there a way we can write the above query in a better way?
Ideally you should validate the input parameters for your collection so that you keep your data types consistent, especially it is beneficial to keep numeric data as numbers rather than strings,
If you want to convert existing items before querying you need to use $map along with $toDouble. After such conversion you can run your query:
db.collection.aggregate([
{
$project: {
data: {
$map: {
input: "$data",
in: {
$mergeObjects: [
"$$this",
{ price: { $toDouble: "$$this.price" } }
]
}
}
}
}
},
{
$match: { "data.price": 2 }
}
])
Mongo Playground
In mongo I have a documents that follow the below pattern :
{
name: "test",
codes: [
[
{
code: "abc",
value: 123
},
{
code: "def",
value: 456
},
],
[
{
code: "ghi",
value: 789
},
{
code: "jkl",
value: 012
},
]
]
}
I'm using an aggregate query (because of joins) and in a $project block I need to return the "name" and the value of the object that has a code of "def" if it exists and an empty string if it doesn't.
I can't simply $unwind codes and $match because the "def" code is not guaranteed to be there.
$filter seems like the right approach as $elemMatch doesn't work, but its not obvious to me how to do this on nested array of arrays.
You can try below query, instead of unwinds & filter this can give you required result with less docs to operate on :
db.collection.aggregate([
/** merge all arrays inside codes array into code array */
{
$addFields: {
codes: {
$reduce: {
input: '$codes',
initialValue: [],
in: { $concatArrays: ["$$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
I am working with MongoDB for the first time.
I have a collection whose each document is roughly of the following form in MongoDB:
{
"name":[
{
"value":"abc",
"created_on":"2020-02-06 06:11:21.340611+00:00"
},
{
"value":"xyz",
"created_on":"2020-02-07 06:11:21.340611+00:00"
}
],
"score":[
{
"value":12,
"created_on":"2020-02-06 06:11:21.340611+00:00"
},
{
"value":13,
"created_on":"2020-02-07 06:11:21.340611+00:00"
}
]
}
How will I form a query so that I get the latest updated values of each field in the given document. I went through Query Embedded Documents, but I wasn't able to figure out how It is.
My expected output is:
{
"name": "xyz",
"score": "13"
}
If you always do push new/latest values to arrays name & score, then you can try below query, it would get last element from array as in general new/latest values will always be added as last element in an array :
db.collection.aggregate([
{ $addFields: { name: { $arrayElemAt: ['$name', -1] }, score: { $arrayElemAt: ['$score', -1] } } },
{ $addFields: { name: '$name.value', score: '$score.value' } }])
Test : MongoDB-Playground
I'm trying to return a specific collection, however, I want to filter an array within the collection. I'm not sure if this is possible. In the example below I'm trying to return the collection with _id: 7ARk3dc2JA8g5pamA and filter out the array object for "candidateUserId": "2". I'm doing this in a Meteorjs application.
Eg: `Collection'
{
"_id": "7ARk3dc2JA8g5pamA",
"jobTitle": "Developer",
"candidateApplication": [
{
"candidateUserId": "1",
"applied": true
},
{
"candidateUserId": "2",
"applied": false
}
]
}
Path: Publish command
return Jobs.find({ _id: 7ARk3dc2JA8g5pamA }, {
$filter: {
input: candidateApplication,
cond: { candidateUserId: { $eq: 1 } }
}
});
Jobs.find({ _id: 7ARk3dc2JA8g5pamA }, { candidateApplication: { $elemMatch: { candidateUserId: 2 } } }
This should return the document with only the _id and the candidateUserId array, but that array will now only contain the object that you want.
{ "_id" : 7ARk3dc2JA8g5pamA, "candidateApplication" : [ { "candidateUserId": 2, "applied": false } ] }
You can then get to the data with candidateApplication[0].candidateUserId and candidateApplication[0].applied
As mentioned in the comments above, if there are more instances of that same candidateUserId, only the first will be returned.
I have the following documents:
[{
"_id":1,
"name":"john",
"position":1
},
{"_id":2,
"name":"bob",
"position":2
},
{"_id":3,
"name":"tom",
"position":3
}]
In the UI a user can change position of items(eg moving Bob to first position, john gets position 2, tom - position 3).
Is there any way to update all positions in all documents at once?
You can not update two documents at once with a MongoDB query. You will always have to do that in two queries. You can of course set a value of a field to the same value, or increment with the same number, but you can not do two distinct updates in MongoDB with the same query.
You can use db.collection.bulkWrite() to perform multiple operations in bulk. It has been available since 3.2.
It is possible to perform operations out of order to increase performance.
From mongodb 4.2 you can do using pipeline in update using $set operator
there are many ways possible now due to many operators in aggregation pipeline though I am providing one of them
exports.updateDisplayOrder = async keyValPairArr => {
try {
let data = await ContestModel.collection.update(
{ _id: { $in: keyValPairArr.map(o => o.id) } },
[{
$set: {
displayOrder: {
$let: {
vars: { obj: { $arrayElemAt: [{ $filter: { input: keyValPairArr, as: "kvpa", cond: { $eq: ["$$kvpa.id", "$_id"] } } }, 0] } },
in:"$$obj.displayOrder"
}
}
}
}],
{ runValidators: true, multi: true }
)
return data;
} catch (error) {
throw error;
}
}
example key val pair is: [{"id":"5e7643d436963c21f14582ee","displayOrder":9}, {"id":"5e7643e736963c21f14582ef","displayOrder":4}]
Since MongoDB 4.2 update can accept aggregation pipeline as second argument, allowing modification of multiple documents based on their data.
See https://docs.mongodb.com/manual/reference/method/db.collection.update/#modify-a-field-using-the-values-of-the-other-fields-in-the-document
Excerpt from documentation:
Modify a Field Using the Values of the Other Fields in the Document
Create a members collection with the following documents:
db.members.insertMany([
{ "_id" : 1, "member" : "abc123", "status" : "A", "points" : 2, "misc1" : "note to self: confirm status", "misc2" : "Need to activate", "lastUpdate" : ISODate("2019-01-01T00:00:00Z") },
{ "_id" : 2, "member" : "xyz123", "status" : "A", "points" : 60, "misc1" : "reminder: ping me at 100pts", "misc2" : "Some random comment", "lastUpdate" : ISODate("2019-01-01T00:00:00Z") }
])
Assume that instead of separate misc1 and misc2 fields, you want to gather these into a new comments field. The following update operation uses an aggregation pipeline to:
add the new comments field and set the lastUpdate field.
remove the misc1 and misc2 fields for all documents in the collection.
db.members.update(
{ },
[
{ $set: { status: "Modified", comments: [ "$misc1", "$misc2" ], lastUpdate: "$$NOW" } },
{ $unset: [ "misc1", "misc2" ] }
],
{ multi: true }
)
Suppose after updating your position your array will looks like
const objectToUpdate = [{
"_id":1,
"name":"john",
"position":2
},
{
"_id":2,
"name":"bob",
"position":1
},
{
"_id":3,
"name":"tom",
"position":3
}].map( eachObj => {
return {
updateOne: {
filter: { _id: eachObj._id },
update: { name: eachObj.name, position: eachObj.position }
}
}
})
YourModelName.bulkWrite(objectToUpdate,
{ ordered: false }
).then((result) => {
console.log(result);
}).catch(err=>{
console.log(err.result.result.writeErrors[0].err.op.q);
})
It will update all position with different value.
Note : I have used here ordered : false for better performance.