Ejemplo del método contar documentos

coll := client.Database("sample_mflix").Collection("movies")
// Specifies a filter to match documents where the "countries" array
// includes a value of "China"
filter := bson.D{{"countries", "China"}}
// Retrieves and prints the estimated number of documents in the collection
estCount, estCountErr := coll.EstimatedDocumentCount(context.TODO())
if estCountErr != nil {
	panic(estCountErr)
}
// Retrieves and prints the number of documents in the collection
// that match the filter
count, err := coll.CountDocuments(context.TODO(), filter)
if err != nil {
	panic(err)
}