How use update function of mongo-go-driver using struct - mongodb

Question

The update function of mongo-go-driver can be called like this.
filter := bson.D{"username", username}
update := bson.D{{"$set",
bson.D{
{"name", person.Name},
},
}}
result, err := collection.UpdateOne(ctx, filter, update)
type Person struct {
ID primitive.ObjectID `json:"_id,omitempty" bson:"_id,omitempty"`
Username string `json:"username,omitempty" bson:"username,omitempty"`
Name string `json:"name,omitempty" bson:"name,omitempty"`
}
But, I need to call the update function using the person struct, without mentioning every field of person struct like this.
filter := bson.D{"username", username}
update := bson.D{{"$set", <<how to convert person struct to bson document?>>}}
result, err := collection.UpdateOne(ctx, filter, update)
How can I convert the person struct to bson document?

Answer 1

ReplaceOne I think is what you're after:
// Use it's ID to replace
filter := bson.M{"_id": existing.ID}
// Create a replacement object using the existing object
replacementObj := existing
replacementObj.SomeFieldToChange = "new-replacement-object"
updateResult, err := coll.ReplaceOne(context.Background(), filter, replacementObj)
assertNotErr(t, err)
assertEquals(t, 1, int(updateResult.ModifiedCount))
A note that ErrNotFound is no longer thrown as it was in mgo - you have to check the Modified/Upserted count.

Answer 2

You could do something like this:
func Update(person Person) error {
pByte, err := bson.Marshal(person)
if err != nil {
return err
}
var update bson.M
err = bson.Unmarshal(pByte, &update)
if err != nil {
return
}
// NOTE: filter and ctx(Context) should be already defined
_, err = collection.UpdateOne(ctx, filter, bson.D{{Key: "$set", Value: update}})
if err != nil {
return err
}
return nil
}

Answer 3

how about marshalling the person struct to bson?
package main
import (
"fmt"
"labix.org/v2/mgo/bson"
)
type person struct {
ID string `json:"_id,omitempty" bson:"_id,omitempty"`
Username string `json:"username,omitempty" bson:"username,omitempty"`
Name string `json:"name,omitempty" bson:"name,omitempty"`
}
func main() {
p := person{
ID: "id",
Username: "uname",
Name: "name",
}
var (
bm []byte
err error
)
if bm, err = bson.Marshal(p); err != nil {
panic(fmt.Errorf("can't marshal:%s", err))
}
update := bson.D{{"$set", bm}}
fmt.Printf("update is:%q\n", update)
}
run:
./sobson
update is:[{"$set" "4\x00\x00\x00\x02_id\x00\x03\x00\x00\x00id\x00\x02username\x00\x06\x00\x00\x00uname\x00\x02name\x00\x05\x00\x00\x00name\x00\x00"}]