add key to nested array with condition - node.js

Question

I have a simple datastructure in mongodb:
{
_id: ObjectID,
name: 'Name',
birthday: '25.05.2001'
items: [
{
_id: ObjectID,
name: 'ItemName',
info: 'ItemInfo',
},
{
_id: ObjectID,
name: 'ItemName',
info: 'ItemInfo',
}
]
}
Now i want a query, that takes a ObjectID (_id) of an item as criteria and gives me back the object with all items in the array AND projects a new field "selected" with value true or false into a field in the result of each array item:
I tried that with this query:
{ $unwind: '$items' },
{
$project: {
selected: {
$cond: { if: { 'items._id': itemObjectID }, then: true, else: false },
},
},
},
but MongoDB gives me back an error:
MongoError: FieldPath field names may not contain '.'.
Have no clue why its not working, any help or ideas? Thank you very much!

Answer 1

What you are missing here is $eq aggregation operator which checks the condition for the equality.
You can try below aggregation here if you want to check for ObjectId then you need to put mongoose.Types.ObjectId(_id)
db.collection.aggregate([
{ "$unwind": "$items" },
{ "$addFields": {
"items.selected": {
"$eq": [
1111,
"$items._id"
]
}
}},
{ "$group": {
"_id": "$_id",
"name": { "$first": "$name" },
"items": {
"$push": {
"_id": "$items._id",
"selected": "$items.selected"
}
}
}}
])
Will give following output
[
{
"_id": ObjectId("5a934e000102030405000000"),
"items": [
{
"_id": 1111,
"selected": true
},
{
"_id": 2222,
"selected": false
}
],
"name": "Name"
}
]
You can check it here

Answer 2

#Ashish: Thank you very much for your help! Your answer helped me to build the right query for me:
db.collection.aggregate([
{
$unwind: "$items"
},
{
$project: {
"items.name": 0,
"birthday": 0
}
},
{
"$addFields": {
"items.selected": {
"$eq": [
1111,
"$items._id"
]
}
}
},
{
$group: {
_id: "$_id",
"name": {
"$first": "$name"
},
items: {
$push: "$items"
}
}
},
{
$match: {
"items._id": {
$eq: 1111
}
}
},
])
and leads to a result that looks like:
[
{
"_id": ObjectId("5a934e000102030405000000"),
"items": [
{
"_id": 1111,
"selected": true
},
{
"_id": 2222,
"selected": false
}
],
"name": "Name"
}
]