I have three collections which I want to merge in one response. I have tried with $lookup but it was not working. The sample schema's and expected response sample attached. The issue is that, it is not merging into one array.
Sample diagram:
Collection 1: product
db.collection("product").findOne({"_id": ObjectId(id), "uid":uid})
Response:{
"_id":"12345",
"uid":"537354",
"name":"toyota"
}
Collection 2: car_types
db.collection('car_types').find({"$or":[{"uid":uid,"car_type":"custom"},{"car_type":"default"}]})
Response: [
{
"_id":"9987",
"car_type":"default",
"title":"Sports"
},
{
"_id":"9988",
"uid":"537354",
"car_type":"custom",
"title":"Trucks"
}
]
Collection 3: car_images
db.collection("car_images").find({"car_id":car_id, "uid":uid})
Response:
[
{
"_id":"56433",
"uid":"537354",
"product_id":"12345",
"type_id":"9987",
"img_src":"cart.jpg"
},
{
"_id":"42453",
"uid":"537354",
"product_id":"12345",
"type_id":"9988",
"img_src":"mini.jpg"
}
]
Expected Response:
{
"product":{
"_id":"12345",
"uid":"537354",
"car_id":"9922",
"name":"toyota"
},
"car_types":[
{
"_id":"9987",
"car_type":"default",
"title":"Sports",
"img_src":"cart.jpg"
},
{
"_id":"9988",
"uid":"537354",
"car_type":"custom",
"title":"Trucks",
"img_src":"mini.jpg"
}
]
}
Try this below aggregation query which uses multiple-join-conditions-with-lookup:
db.product.aggregate([
/** lookup on `car_types` to pull in docs where if `uid are equal + car_type is custom` or `car_type is default` */
{
$lookup: {
from: "car_types",
let: { productUID: "$uid" }, /** Create a local variable */
pipeline: [
{
$match: {
$expr: {
"$or": [
{ $and: [ { $eq: [ "$uid", "$$productUID" ] }, { $eq: [ "$car_type", "custom" ] } ] },
{ $eq: [ "$car_type", "default" ] }
]
}
}
}
],
as: "car_types"
}
},
/** lookup on `car_images`, to pull in docs where if `type_id` exists in array of `car_types._id` or uid's are equal */
{
$lookup: {
from: "car_images",
let: { car_typesID: "$car_types._id", productUID: "$uid" },
pipeline: [
{
$match: { $expr: { $or: [ { $in: [ "$type_id", "$$car_typesID" ] }, { $eq: [ "$uid", "$$productUID" ] } ] } }
}
],
as: "car_images"
}
}
])
Test : mongoplayground
Related
I have a collection and its documents look like:
{
_id: ObjectId('111111111122222222223333'),
my_array: [
{
id: ObjectId('777777777788888888889999')
name: 'foo'
},
{
id: ObjectId('77777777778888888888555')
name: 'foo2'
}
//...
]
//more attributes
}
However, some documents have my_array: [{}] (with one element which is an empty array).
How can I add conditionally a projection or remove it?
I have to add it to a mongo pipeline at the end of the query, and I want to get my_array only when it has at least one element which is not an empty object. If there's an empty object remove it.
I tried with $cond and $eq in a projection stage but it is not supported. Any suggestion to solve this?
Suppose you have documents like this with my_array field:
{ "my_array" : [ ] }
{ "my_array" : [ { "a" : 1 } ] } // #(1)
{ "my_array" : null }
{ "some_fld" : "some value" }
{ "my_array" : [ { } ] }
{ "my_array" : [ { "a" : 2 }, { "a" : 3 } ] } // #(2)
And, the following aggregation will filter and the result will have the two documents (1) and (2):
db.collection.aggregate([
{
$match: {
$expr: {
$and: [
{ $eq: [ { $type: "$my_array" }, "array" ] },
{ $gt: [ { $size: "$my_array" }, 0 ] },
{ $ne: [ [{}], "$my_array" ] }
]
}
}
}
])
This also works with a find method:
db.collection.find({
$expr: {
$and: [
{ $eq: [ { $type: "$my_array" }, "array" ] },
{ $gt: [ { $size: "$my_array" }, 0 ] },
{ $ne: [ [{}], "$my_array" ] }
]
}
})
To remove the my_array field, from a document when its empty, then you try this aggregation:
db.collection.aggregate([
{
$addFields: {
my_array: {
$cond: [
{$and: [
{ $eq: [ { $type: "$my_array" }, "array" ] },
{ $gt: [ { $size: "$my_array" }, 0 ] },
{ $ne: [ [{}], "$my_array" ] }
]},
"$my_array",
"$$REMOVE"
]
}
}
}
])
The result:
{ }
{ "my_array" : [ { "a" : 1 } ] }
{ }
{ "a" : 1 }
{ }
{ "my_array" : [ { "a" : 2 }, { "a" : 3 } ] }
You can't do that in a query, however in an aggregations you can add $filter to you pipeline, like so:
db.collection.aggregate([
{
$project: {
my_array: {
$filter: {
input: "$my_array",
as: "elem",
cond: {
$ne: [
{},
"$$elem"
]
}
}
}
}
}
])
Mongo Playground
However unless this is "correct" behavior I suggest you clean up your database, it's much simpler to maintain "proper" structure than to update all your queries everywhere.
You can use this update to remove these objects:
db.collection.update({
"myarray": {}
},
[
{
"$set": {
"my_array": {
$filter: {
input: "$my_array",
as: "elem",
cond: {
$ne: [
{},
"$$elem"
]
}
}
}
}
},
],
{
"multi": false,
"upsert": false
})
Mongo Playground
I have a class model which has field ref.
I'm trying to fetch only records that match the condition in lookup.
so what i did:
{
$lookup: {
from: 'fields',
localField: "field",
foreignField: "_id",
as: 'FieldCollege',
},
},
{
$addFields: {
"FieldCollege": {
$arrayElemAt: [
{
$filter: {
input: "$FieldCollege",
as: "field",
cond: {
$eq: ["$$field.level", req.query.level]
}
}
}, 0
]
}
}
},
The above code works fine and returning the FieldCollege if the cond is matched.
but the thing is, i wanted to return the class records only if the FieldCollege is not empty.
I'm totally new to mongodb. so i tried something like this:
{
$match: {
'FieldCollege': { $exists: true, $ne: [] }
}
},
Obv this didn't work.
does mongodb support something like this or am i complicating things?
EDIT:
the result from the above code:
"Classes": [
{
"_id": "613245664c6ea614e001fcef",
"name": "test",
"language": "en",
"year_cost": "3232323",
"FieldCollege":[] // with $unwind
}
],
expected Result:
"Classes": [
// FieldCollege is empty
],
I think the good option is to use lookup with pipeline, and see the final version of your query,
$lookup with fields collection and match your both conditions
$limit to result one document
$match FieldCollege is not empty []
$addElemAt to get first element from result FieldCollege
[
{
$lookup: {
from: "fields",
let: { field: "$field" },
pipeline: [
{
$match: {
$and: [
{ $expr: { $eq: ["$$field", "$_id"] } },
{ level: req.query.level }
]
}
},
{ $limit: 1 }
],
as: "FieldCollege"
}
},
{ $match: { FieldCollege: { $ne: [] } } },
{
$addFields: {
FieldCollege: { $arrayElemAt: ["$FieldCollege", 0] }
}
}
]
I need to join two collection with two conditions.
products:
{
...
sku: "4234",
organizationId: ObjectId("asdasdasd);
...
};
order_history:
{
...
itemSku: "4234",
organizationId: ObjectId("asdasdasd);
...
}
I chose pipeline approach:
$lookup: {
from: 'order_history',
let: { foreign_sku: "$itemSku", foreign_organizationId: "$organizationId" },
pipeline: [
{
$match: {
$expr: {
$and: [
{ $eq: ["$organizationId", "$$foreign_organizationId"] },
{ $eq: ["$sku", "$$foreign_sku" ] }
]
}
}
}
],
as: 'order_history'
}
I wrote it on base of Mongo Documentation, but my conditions are ignored.
I have scalar multiplication in result. Where is my mistake?
I already mention in the comment and the code is below
db.products.aggregate([
{
$lookup: {
from: "order_history",
let: {
foreign_sku: "$sku",
foreign_organizationId: "$organizationId"
},
pipeline: [
{
$match: {
$expr: {
$and: [
{
$eq: [
"$organizationId",
"$$foreign_organizationId"
]
},
{
$eq: [
"$itemSku",
"$$foreign_sku"
]
}
]
}
}
}
],
as: "order_history"
}
}
])
Working Mongo playground
I am trying to get some other information from titleInfo collection using siteId of regCodes collection
I have two collections
regCodes
{
"siteId" : "123A",
"registration_code" : "ABC",
"used_flag" : true,
"Allowed_Use" : 1,
"Remaining_Use" : 0,
"BatchId" : "SNGL",
"CodeDuration" : 180
}
titleInfo
{
"title" : "Principles of Microeconomics",
"product_form_detail" : "EPUB",
"final_binding_description" : "Ebook",
"vitalsource_enabled" : false,
"reading_line" : "with InQuizitive and Smartwork5",
"volume" : "",
"protected_content" : {
"ebookSiteIds" : [
"123A"
],
"studySpaceSiteIds" : [],
"iqSiteIds" : []
}
}
below query not working, getting 'regcodeData' as empty array.
using mongodb version 3.6.18
db.getCollection('regCodes').aggregate([
{
$match: {
registration_code: 'ABC'
}
},
{
$lookup: {
from: "titleInfo",
let: {
regcode_siteId: "$siteId"
},
pipeline: [
{
$match: {
$expr: {
$or: [
{
$eq: [
"$protected_content.ebookSiteIds",
"$$regcode_siteId"
]
},
{
$eq: [
"$protected_content.studySpaceSiteIds",
"$$regcode_siteId"
]
},
{
$eq: [
"$protected_content.iqSiteIds",
"$$regcode_siteId"
]
}
]
}
}
}
],
as: "regcodeData"
}
}
])
below query is working as expected
db.getCollection('titleInfo').find({
$or: [
{
"protected_content.ebookSiteIds": "123A"
},
{
"protected_content.studySpaceSiteIds": "123A"
},
{
"protected_content.iqSiteIds": "123A"
}
]
})
You just need to unwind the arrays, by using $unwind operator with preserveNullAndEmptyArrays option set to true.
Updated Query:
db.regCodes.aggregate([
{
$match: {
registration_code: "ABC"
}
},
{
$lookup: {
from: "titleInfo",
let: {
regcode_siteId: "$siteId"
},
pipeline: [
{
$unwind: {
path: "$protected_content.ebookSiteIds",
preserveNullAndEmptyArrays: true
}
},
{
$unwind: {
path: "$protected_content.studySpaceSiteIds",
preserveNullAndEmptyArrays: true
}
},
{
$unwind: {
path: "$protected_content.iqSiteIds",
preserveNullAndEmptyArrays: true
}
},
{
$match: {
$expr: {
$or: [
{
$eq: [
"$protected_content.ebookSiteIds",
"$$regcode_siteId"
]
},
{
$eq: [
"$protected_content.studySpaceSiteIds",
"$$regcode_siteId"
]
},
{
$eq: [
"$protected_content.iqSiteIds",
"$$regcode_siteId"
]
}
]
}
}
}
],
as: "regcodeData"
}
}
])
MongoPlayGroundLink
My bad trying to match array with string
Answer is as below
db.getCollection('regCodes').aggregate([
{
$match: {
registration_code: 'ABC'
}
},
{
$lookup: {
from: "titleInfo",
let: {
regcode_siteId: "$siteId"
},
pipeline: [
{
$match: {
$expr: {
$or: [
{
$in: [
"$$regcode_siteId",
"$protected_content.ebookSiteIds"
]
},
{
$in: [
"$$regcode_siteId",
"$protected_content.studySpaceSiteIds"
]
},
{
$in: [
"$$regcode_siteId",
"$protected_content.iqSiteIds"
]
}
]
}
}
}
],
as: "regcodeData"
}
}
])
my collection in mongo db like this:
{
name:"mehdi",
grades:
[
{
a:1,
b:[2,3,4],
c:3,
d:4,
e:5
},
{
a:11,
b:[22,33,44],
c:33,
d:44,
e:55
}
]
}
I want to get a result with project op to give me a specific field in an array like this:
{
name:"mehdi",
grades:
[
{
a:1,
b:2
},
{
a:11,
b:22
}
]
}
how can I do this?
You can use $map to select a,b fields using $type to determine whether it's an array or number:
db.collection.aggregate([
{
$project: {
grades: {
$map: {
input: "$grades",
in: {
a: { $cond: [ { $eq: [ { $type: "$$this.a" }, "array" ] }, { $arrayElemAt: [ "$$this.a", 0 ] }, "$$this.a" ] },
b: { $cond: [ { $eq: [ { $type: "$$this.b" }, "array" ] }, { $arrayElemAt: [ "$$this.b", 0 ] }, "$$this.b" ] },
}
}
}
}
}
])
Mongo Playground