fixed cases Drivers and Dialects are not registered, where sql driver is loaded after xorm.init(), using explicit call to register Drivers and Dialects upon xorm.NewEngine() call

xorm.go

@@ -4,21 +4,25 @@ import (
 	"database/sql"
 	"errors"
 	"fmt"
+	"github.com/go-xorm/core"
 	"os"
 	"reflect"
 	"runtime"
 	"sync"
 	"time"
-
-	"github.com/go-xorm/core"
 )
 
 const (
 	Version string = "0.4"
 )
 
-func init() {
+// !nashtsai! implicit register drivers and dialects is no good, as init() can be called before sql driver got registered
+// func init() {
+// 	regDrvsNDialects()
+// }
 
+func regDrvsNDialects() bool {
+	if core.RegisteredDriverSize() == 0 {
 		providedDrvsNDialects := map[string]struct {
 			dbType     core.DbType
 			getDriver  func() core.Driver
@@ -36,10 +40,17 @@ func init() {
 		for driverName, v := range providedDrvsNDialects {
 			_, err := sql.Open(driverName, "")
 			if err == nil {
+				// fmt.Printf("driver succeed: %v\n", driverName)
 				core.RegisterDriver(driverName, v.getDriver())
 				core.RegisterDialect(v.dbType, v.getDialect())
+			} else {
+				// fmt.Printf("driver failed: %v | err: %v\n", driverName, err)
 			}
 		}
+		return true
+	} else {
+		return false
+	}
 }
 
 func close(engine *Engine) {
@@ -49,6 +60,7 @@ func close(engine *Engine) {
 // new a db manager according to the parameter. Currently support four
 // drivers
 func NewEngine(driverName string, dataSourceName string) (*Engine, error) {
+	regDrvsNDialects()
 	driver := core.QueryDriver(driverName)
 	if driver == nil {
 		return nil, errors.New(fmt.Sprintf("Unsupported driver name: %v", driverName))