How to avoid adding duplicate objects to an array in MongoDB - mongodb

Question

this is my schema:
new Schema({
code: { type: String },
toy_array: [
{
date:{
type:Date(),
default: new Date()
}
toy:{ type:String }
]
}
this is my db:
{
"code": "Toystore A",
"toy_array": [
{
_id:"xxxxx", // automatic
"toy": "buzz"
},
{
_id:"xxxxx", // automatic
"toy": "pope"
}
]
},
{
"code": "Toystore B",
"toy_array": [
{
_id:"xxxxx", // automatic
"toy": "jessie"
}
]
}
I am trying to update an object. In this case I want to update the document with code: 'ToystoreA' and add an array of subdocuments to the array named toy_array if the toys does not exists in the array.
for example if I try to do this:
db.mydb.findOneAndUpdate({
code: 'ToystoreA,
/*toy_array: {
$not: {
$elemMatch: {
toy: [{"toy":'woddy'},{"toy":"buzz"}],
},
},
},*/
},
{
$addToSet: {
toy_array: {
$each: [{"toy":'woddy'},{"toy":"buzz"}],
},
},
},
{
new: false,
}
})
they are added and is what I want to avoid.
how can I do it?
[
{
"code": "Toystore A",
"toy_array": [
{
"toy": "buzz"
},
{
"toy": "pope"
}
]
},
{
"code": "Toystore B",
"toy_array": [
{
"toy": "jessie"
}
]
}
]
In this example [{"toy":'woddy'},{"toy":"buzz"}] it should only be added 'woddy' because 'buzz' is already in the array.
Note:when I insert a new toy an insertion date is also inserted, in addition to an _id (it is normal for me).

Answer 1

As you're using $addToSet on an object it's failing for your use case for a reason :
Let's say if your document look like this :
{
_id: 123, // automatically generated
"toy": "buzz"
},
{
_id: 456, // automatically generated
"toy": "pope"
}
and input is :
[{_id: 789, "toy":'woddy'},{_id: 098, "toy":"buzz"}]
Here while comparing two objects {_id: 098, "toy":"buzz"} & {_id: 123, "toy":"buzz"} - $addToSet consider these are different and you can't use $addToSet on a field (toy) in an object. So try below query on MongoDB version >= 4.2.
Query :
db.collection.updateOne({"_id" : "Toystore A"},[{
$addFields: {
toy_array: {
$reduce: {
input: inputArrayOfObjects,
initialValue: "$toy_array", // taking existing `toy_array` as initial value
in: {
$cond: [
{ $in: [ "$$this.toy", "$toy_array.toy" ] }, // check if each new toy exists in existing arrays of toys
"$$value", // If yes, just return accumulator array
{ $concatArrays: [ [ "$$this" ], "$$value" ] } // If No, push new toy object into accumulator
]
}
}
}
}
}])
Test : aggregation pipeline test url : mongoplayground
Ref : $reduce
Note :
You don't need to mention { new: false } as .findOneAndUpdate() return old doc by default, if you need new one then you've to do { new: true }. Also if anyone can get rid of _id's from schema of array objects then you can just use $addToSet as OP was doing earlier (Assume if _id is only unique field), check this stop-mongoose-from-creating-id-property-for-sub-document-array-items.