Mgo SetBSON to mongo golang driver

Working with Data Drivers
1

I’m migration our app from mgo to the official mongo go driver, but I’m stuck with the mgo SetBSON migration, this is my old code and I don’t know how to do this using the new driver:

type MyStruct struct {
	ID            primitive.ObjectID `bson:"_id"`
	Ends          time.Time          `bson:"ends"`
}
func (st *MyStruct) SetBSON(raw bson.Raw) error {
	decoded := new(struct {
		ID            primitive.ObjectID `bson:"_id"`
		Ends          string             `bson:"ends"`
	})

	bsonErr := raw.Unmarshal(decoded)
	if bsonErr != nil {
		return bsonErr
	}

	const dateFormat = "2006-01-02"
	
	end, endErr := time.ParseInLocation(dateFormat, decoded.Ends, constants.NYCLoc)
	if endErr != nil {
		return endErr
	}

	st.ID = decoded.ID
	st.Ends = time.Date(ey, em, ed, 23, 59, 0, 0, constants.NYCLoc)
	return nil
}

The core is, we have a struct that in mongo stores the “end” field as a string that looks like “20200402”. When the driver reads the bson from mongo, I need to decode the struct and convert the string value from the field “end” into a time.Time Go type.

I hope I can avoid having to create a new custom “field” type for the end mongo field, because the app assumes a time.Time all over.

Thanks

2

Hi @Diego_Medina,

You can do this using the UnmarshalBSON hook for the driver. This is similar to the UnmarshalJSON hook in the encoding/json library. I wrote up an example of this in Go Playground - The Go Programming Language. It’s worth noting that version 1.3.0 of the driver introduced a custom BSON registry to mimic parts of mgo BSON behavior to mitigate BSON issues for users when migrating to the official driver. This registry supports GetBSON/SetBSON. You can see documentation for that at mgocompat package - go.mongodb.org/mongo-driver/bson/mgocompat - Go Packages.

2 Likes
3

Thanks you! your example was just what I needed.

4

I was trying to understand why not use the bsoncodec package - go.mongodb.org/mongo-driver/bson/bsoncodec - Go Packages.

Is this what you mean by

It’s worth noting that version 1.3.0 of the driver introduced a custom BSON registry

5

@Yehuda_Makarov You can use the bsoncodec package and write a custom codec for this use case, but implementing the bson.Unmarshaler interface works just as well.

Version 1.3.0 of the driver introduced a new mgocompat package that provides a custom BSON registry (mgocompat.Registry) to mimic some of mgo’s BSON behavior. This includes adding support for GetBSON and SetBSON methods. You can see more details about it at mgocompat package - go.mongodb.org/mongo-driver/bson/mgocompat - Go Packages. Search for Setter on that page to see how the SetBSON method should be implemented. If you choose to use this registry, you can enable it for a Client as follows:

opts := options.Client().SetRegistry(mgocompat.Registry)
client, err := mongo.Connect(ctx, opts)
// handle err, defer Disconnect(), etc

Feel free to add another comment here or open a new question on these forums if you have any follow-up questions about the new registry.

– Divjot

2 Likes