The package provides a reader that can make a lookup into maxmind db file and fetch only requested fields
Example
db, err := maxminddb.Open("path/to/GeoIP2-City.mmdb")
if err != nil {
t.Error(err)
}
ip := net.ParseIP("216.160.83.56")
result := make(map[string]interface{})
fields := []string{
"location.metro_code",
"subdivisions.0.names.en"
}
if err = db.Lookup(ip, fields, result); err != nil {
log.Error("couldn't get the record due to %s", err)
}