bson.D vs bson.M

from bson package go doc,

M is an unordered representation of a BSON document. This type should be used when the order of the elements does not matter. This type is handled as a regular map[string]interface{} when encoding and decoding. Elements will be serialized in an undefined, random order. If the order of the elements matters, a D should be used instead.

But official mongodb reference uses bson.D everywhere even if order does not matter in examples. such as docs in Specify a Query - Go Driver v1.16

And using struct bson.D like bson.D{{"_id", 2158}} cause lint error UnusedExpr. IMHO in most cases bson.M is better choice

inconsistent BSONOptions

to json tag be parsed by mongodb driver, options.BSONOptions{UseJSONStructTags: true} must be provided when initializing mongodb client

bsonOpts := &options.BSONOptions {
    UseJSONStructTags: true,
    NilSliceAsEmpty: true,
}

clientOpts := options.Client().
    ApplyURI("<connection string>").
    SetBSONOptions(bsonOpts)

client, err := mongo.Connect(context.TODO(), clientOpts)

• I think UseJSONStructTags must be default to true

If you define struct with only json fields and start to query or insert, inconsistency happends

• If you want to insert struct with only json tags, you need UseJSONStructTags to be true
• If you want to query struct with only json tags, you don’t need UseJSONStructTags to be true

This happens when using bson.M which is internally just a map[string]any

struct embedding needs bson:inline

There is no way to embed struct without using bson tags. Need to add bson:inline if struct nesting is needed even with UseJSONStructTags to be true

type Outer struct {
	Inner `bson:inline`
	other int `json:"other"`
}

• This is documented in Work with BSON - Go Driver v1.16