Go Mongo Driver Retrieve Schemaless Documents - mongodb

Question

While working with Mongo Go Driver I want to retrieve Schemaless Documents.
I am able to retrieve documents using bson.M json:",inline" bson:",inline"
But this adds extra "M" key in json when i try to Decode to a struct
type Product struct {
ID primitive.ObjectID `bson:"_id"`
ProductId string `bson:"product_id" json:"product_id"`
bson.M `json:",inline" bson:",inline"`
}
Output:-
{
"id":"<ObjectId>",
"M":{
"some":""
}
}
But instead what i want how it is stored in Mongo.
{
"id":"<ObjectId>",
"some":""
}
I cant use directly something like this as I want to cast it to struct to work with some properties
var pr bson.M
err := p.FindOne(ctx, &p.options,query, &pr)
How can I remove that extra key which is getting added while converting schemaless Documents from Mongo?
Do I need to explicitly overwrite MarshalJSON() or is there something provided using Tags?

Answer 1

How can I remove that extra key which is getting added while converting schemaless Documents from Mongo?
You can just define a field mapping name, which will be flattened when marshalled. For example:
type Product struct {
ID primitive.ObjectID `bson:"_id"`
ProductId string `bson:"product_id"`
Others bson.M `bson:",inline"`
}
When you decode a document, you'll see that it will include other fields without the Others name. For example if you have a document:
{
"_id": ObjectId("5e8d330de85566f5a0557ea4"),
"product_id": "foo",
"some": "x",
"more": "y"
}
doc := Product{}
err = cur.Decode(&doc)
fmt.Println(doc)
// Outputs
// {ObjectID("5e8d330de85566f5a0557ea4") foo map[more:y some:x]}
I cant use directly something like this as I want to cast it to struct to work with some properties
You can use this directly for a query predicate. For example:
// After decoding 'doc' to product
var result bson.M
err := collection.FindOne(context.TODO(), doc).Decode(&result)
Tested using MongoDB Go driver v1.3.2
UPDATED:
If you would like to return JSON, you could use bson.MarshalExtJSON(). This should be easier as well in terms of dealing with objects that don't exist in JSON. i.e. ObjectId. For example:
// After decoding 'doc' to product
ejson, err := bson.MarshalExtJSON(doc, true, false)
fmt.Println(string(ejson))