1 files changed, 21 insertions, 1 deletions
diff --git a/invoice/service.go b/invoice/service.go
index 3dcc5e2..9408a0d 100644
--- a/invoice/service.go
+++ b/invoice/service.go
@@ -25,8 +25,28 @@ import (
 func getNewInvoiceNumber(userId uint) (uint, error) {
 	var i uint
 
+	// check if number of invoices is 0
+	var count int64
+	err := db.Model(&Invoice{}).
+		Where("user_id = ?", userId).
+		Count(&count).
+		Error
+
+	if err != nil {
+		return i, err
+	}
+
+	// if no records exist, then invoice number should be 1
+	if count == 0 {
+		return 1, nil
+	}
+
+	// if records exist, get max invoice number
+	// NOTE: if there are gaps in invoice numbers,
+	// they won't be filled and the series would continue
+	// from the greatest invoice number.
 	row := db.Model(&Invoice{}).Where("user_id = ?", userId).Select("max(invoice_number)").Row()
-	err := row.Scan(&i)
+	err = row.Scan(&i)
 
 	return i + 1, err
 }