fix(server): sql server not allow multiple null

multiple null values for unique constrained column
is not allowed on sqlserver

Resolves #278

Author: lakhansamani

server/db/providers/sql/provider.go

@@ -1,6 +1,7 @@
 package sql
 
 import (
+	"fmt"
 	"log"
 	"os"
 	"time"
@@ -21,6 +22,16 @@ type provider struct {
 	db *gorm.DB
 }
 
+const (
+	phoneNumberIndexName  = "UQ_phone_number"
+	phoneNumberColumnName = "phone_number"
+)
+
+type indexInfo struct {
+	IndexName  string `json:"index_name"`
+	ColumnName string `json:"column_name"`
+}
+
 // NewProvider returns a new SQL provider
 func NewProvider() (*provider, error) {
 	var sqlDB *gorm.DB
@@ -65,6 +76,32 @@ func NewProvider() (*provider, error) {
 	if err != nil {
 		return nil, err
 	}
+
+	// unique constraint on phone number does not work with multiple null values for sqlserver
+	// for more information check https://stackoverflow.com/a/767702
+	if dbType == constants.DbTypeSqlserver {
+		var indexInfos []indexInfo
+		// remove index on phone number if present with different name
+		res := sqlDB.Raw("SELECT i.name AS index_name, i.type_desc AS index_algorithm, CASE i.is_unique WHEN 1 THEN 'TRUE' ELSE 'FALSE' END AS is_unique, ac.Name AS column_name FROM sys.tables AS t INNER JOIN sys.indexes AS i ON t.object_id = i.object_id INNER JOIN sys.index_columns AS ic ON ic.object_id = i.object_id AND ic.index_id = i.index_id INNER JOIN sys.all_columns AS ac ON ic.object_id = ac.object_id AND ic.column_id = ac.column_id WHERE t.name = 'authorizer_users' AND SCHEMA_NAME(t.schema_id) = 'dbo';").Scan(&indexInfos)
+		if res.Error != nil {
+			return nil, res.Error
+		}
+
+		for _, val := range indexInfos {
+			if val.ColumnName == phoneNumberColumnName && val.IndexName != phoneNumberIndexName {
+				// drop index & create new
+				if res := sqlDB.Exec(fmt.Sprintf(`ALTER TABLE authorizer_users DROP CONSTRAINT "%s";`, val.IndexName)); res.Error != nil {
+					return nil, res.Error
+				}
+
+				// create index
+				if res := sqlDB.Exec(fmt.Sprintf("CREATE UNIQUE NONCLUSTERED INDEX %s ON authorizer_users(phone_number) WHERE phone_number IS NOT NULL;", phoneNumberIndexName)); res.Error != nil {
+					return nil, res.Error
+				}
+			}
+		}
+	}
+
 	return &provider{
 		db: sqlDB,
 	}, nil