Mongo indexing on nested object - node.js

Question

My mongodb collection's structure looke like this,
{
paymentTree: {
t1: { from: "id-123", to: "id-2334", },
t2: { from: "id-1443", to: "id-567", },
t3: { from: "id-76567", to: "id-2334", },
tn: { from: "id-12n", to: "id-233n", }
}
How can index field 'to' in paymentTree?

Answer 1

Currently it is not possible to create index in dynamic object key,
If you want to achieve anyway then I would suggest if you could transform your schema structure to The Attribute Pattern,
change paymentTree object type to array type,
change object to array in key-value pairs, k for tree's dynamic key and v for { from, to } object,
{
paymentTree: [
{
"k": "t1",
"v": { "from": "id-123", "to": "id-2334" }
},
{
"k": "t2",
"v": { "from": "id-1443", "to": "id-567" }
},
{
"k": "t3",
"v": { "from": "id-76567", "to": "id-2334" }
},
{
"k": "tn",
"v": { "from": "id-12n", "to": "id-233n" }
}
]
}
Benefits of this structure:
Create Multikey Single Field Index on to:
You can create multikey indexes on array fields that contain nested objects,
db.collection.createIndex({ "paymentTree.v.to": 1 });
Create Multikey Compound Index on k and to:
db.collection.createIndex({ "paymentTree.k": 1, "paymentTree.v.to": 1 });
Push object to array:
You can insert object to paymentTree array using $push in update methods (updateOne and updateMany).
Pull object from array:
You can remove specific object on the base of k from paymentTree array using $pull in update methods (updateOne and updateMany).
Match conditions:
You can easily match conditions using conditional operators,
Ex.1:
{ "paymentTree.k": "t1" }
Ex.2:
{ "paymentTree.v.to": "id-2334" } // or { "paymentTree.v.from": "id-123" }
Ex.3:
{
"paymentTree": {
"$elemMatch": {
"k": "t1",
"v.to": "id-2334" // or "v.from": "id-123"
}
}
}
How can i easily select like paymentTree.t1, ..:
In Query:
There is a operator called $arrayToObject, you can convert paymentTree array to object in projection stages ($project, $addFields, $set) see Playground,
The find() and findOne() projection can accept aggregation expressions and syntax from MongoDB v4.4 projection consistent with aggregation’s $project stage,
Outside Query:
You need to convert peymentTree array to object format in your client side language (go, node.js, etc.).

Answer 2

this works for me
_, err = db.Comments.Indexes().CreateOne(db.Ctx, mongo.IndexModel{Keys: bson.M{"t1.to": 1}})
if err != nil {
panic(err)
}