Export the field names.
type Customer struct {
Id bson.ObjectId `bson:"_id,omitempty"`
ID int `bson:"id"`
FirstName string `bson:"firstName"`
Surname string `bson:"surname"`
Gender string `bson:"gender"`
Address1 string `bson:"address1"`
Address2 string `bson:"address2"`
City string `bson:"city"`
State_region string `bson:"state_region"`
County_province string `bson:"county_province"`
PostalCode string `bson:"postalCode"`
Country string `bson:"country"`
Acct_bal float64 `bson:"acct_bal"`
Status string `bson:"status"`
}
The BSON encoder serializes exported fields only. Other serializers such as encoding/json and encoding/gob also work with exported fields only.