How to add a position field on each document of a subdocument array with mongodb aggregations?

Question

I'm currently working on a matching algorithm that calculates a score between two differents products lists.
I'm using mongodb aggregations to add a matching-score field calculated with differents arguments. Actually, the algorithm needs to know the position of each product in the list. So I thought to dynamically add a position field on each product to use it later.
I don't know which mongodb aggregation operator I have to use. Maybe someone can help me ?

Here is my list model :

const listSchema = mongoose.Schema({
    type: { type: mongoose.Schema.Types.ObjectId, ref: "ListType", required: true },
    links: [{
        brand: { type: mongoose.Schema.Types.ObjectId, ref: "Brand", required: true },
        work: { type: mongoose.Schema.Types.ObjectId, ref: "Product" },
    }],
    associatedUser: { type: mongoose.Schema.Types.ObjectId, ref: "User", required: true }
}, { versionKey: false });

In advance thank you,
Pierre

So you wanted to add positions to objects in links array just in reads via aggregation but not to update actual doc in collection ? — whoami - fakeFaceTrueSoul
– whoami - fakeFaceTrueSoul, Commented Mar 20, 2020 at 18:30
Does this answer your question? Get index of given element in array field in MongoDB — whoami - fakeFaceTrueSoul
– whoami - fakeFaceTrueSoul, Commented Mar 20, 2020 at 18:36

Joe · Accepted Answer · 2020-03-20 23:18:18Z

1

One method is to use the $reduce operator, which can be done in an aggregation pipeline, or as of MongoDB 4.2 in an update.

This example replaces an 'arrayField' containing

["Hello","World"]

with an array of objects like

[{index:0,value:"Hello"},{index:1,value:"World"}]

db.collection.update({},[{$set:{
      arrayField:{
            $reduce:{
                 input:"$arrayField",
                 initialValue:[],
                 in:{ $push:[
                       "$$value",
                       {index:{$size:"$$value"},
                        value:"$$this"}
                 ]}
            }
     }
}}])

answered Mar 20, 2020 at 23:18

Joe

29k4 gold badges25 silver badges50 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

How to add a position field on each document of a subdocument array with mongodb aggregations?

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related