fix: fix postgresql support (#606)

* fix postgresql support

fixes #517

* fix: fix pg support

* chore: delete useless code

---------

Co-authored-by: JustSong <songquanpeng@foxmail.com>

model/main.go

@@ -42,6 +42,7 @@ func chooseDB() (*gorm.DB, error) {
 		if strings.HasPrefix(dsn, "postgres://") {
 			// Use PostgreSQL
 			common.SysLog("using PostgreSQL as database")
+			common.UsingPostgreSQL = true
 			return gorm.Open(postgres.New(postgres.Config{
 				DSN:                  dsn,
 				PreferSimpleProtocol: true, // disables implicit prepared statement usage