Go-MongoDriver decoding JSON array weirdly - mongodb

Question

Heyho party people,
I've recently took up learning Go and started working on a small side project which includes a API written using the Go Fiber library.
All the necessery data is stored in MongoDB with the following schema
{
"ObjectId": {
"name": "name",
"url": "url",
"dateAdded": "date",
"data": [{
"timestamp 1": "price 1"
},
{
"timestamp 2": "price 2"
}
]
}
}
The item type looks like this:
type Item struct {
ID primitive.ObjectID `json:"_id" bson:"_id"`
Name string `json:"name" bson:"name"`
URL string `json:"url" bson:"url"`
DateAdded string `json:"dateAdded" bson:"dateAdded"`
Data []interface{} `json:"data" bson:"data"`
}
Whenever I query a stored item with
err = collection.FindOne(context.TODO(), filter).Decode(&item)
each map inside of the data-array is wrapped in another array =>
{ test url 2021-04-16 [[{2021-04-16 99.99}] [{2021-04-17 109.99}]] }
instead of
{ test url 2021-04-16 [{2021-04-16 99.99}, {2021-04-17 109.99}] }
Does anybody have an idea on how to fix this?
Thanks in advance!

Answer 1

OK, I've found a way to fix this behaviour for my use case.
As mentioned above, the MongoDB-driver for Go wraps each entry of an array into another respective array, which leads to a nested array.
After trying around for some time I found out, that inserting the document into your collection like the following example,
db.collection.insertOne({ name: "Name", url: "URL", dateAdded: "2021-04-25", data: { "2021-04-25": 9.99, "2021-04-26": 19.99 } })
then the result of a query performed in your program looks like this:
{ ObjectID("60858245f8805dc57a716500") Name URL 2021-04-25 [{ 2021-04-25 9.99 } { 2021-04-26 19.99 }] }
This means, that the JSON-schema should look like this
{
"ObjectId": {
"name": "name",
"url": "url",
"dateAdded": "date",
"data": {
"2021-04-25": 9.99,
"2021-04-26": 19.99
}
}
}
Sadly, I was not able to find out what is actually causing this odd behaviour, but I hope this helps anybody encountering this (or a similar) problem.
EDIT
Changing the type of the Data-field to []bson.M, as mkopriva said in the comments below, fixed it.
type Item struct {
ID primitive.ObjectID `json:"_id" bson:"_id"`
Name string `json:"name" bson:"name"`
URL string `json:"url" bson:"url"`
DateAdded string `json:"dateAdded" bson:"dateAdded"`
Data []bson.M `json:"data" bson:"data"`
}
This way the original JSON-schema does not have to be adapted to the workaround.
{
"ObjectId":{
"name":"name",
"url":"url",
"dateAdded":"date",
"data": [
{
"2021-04-25": 9.99
},
{
"2021-04-26": 19.99
}
]
}
}