Implementatoin of possibility to reconnect

callback_create.go

@@ -50,6 +50,8 @@ func updateTimeStampForCreateCallback(scope *Scope) {
 // createCallback the callback used to insert data into database
 func createCallback(scope *Scope) {
 	if !scope.HasError() {
+		scope.db.reconnectGuard.Wait()
+
 		defer scope.trace(NowFunc())
 
 		var (

callback_delete.go

@@ -28,6 +28,8 @@ func beforeDeleteCallback(scope *Scope) {
 // deleteCallback used to delete data from database or set deleted_at to current time (when using with soft delete)
 func deleteCallback(scope *Scope) {
 	if !scope.HasError() {
+		scope.db.reconnectGuard.Wait()
+
 		var extraOption string
 		if str, ok := scope.Get("gorm:delete_option"); ok {
 			extraOption = fmt.Sprint(str)

callback_query.go

@@ -16,6 +16,7 @@ func init() {
 // queryCallback used to query data from database
 func queryCallback(scope *Scope) {
 	defer scope.trace(NowFunc())
+	scope.db.reconnectGuard.Wait()
 
 	var (
 		isSlice, isPtr bool

callback_reconnect.go

@@ -0,0 +1,62 @@
+package gorm
+
+import (
+	"time"
+)
+
+//define callbacks to reconnect in case of failure
+func init() {
+	DefaultCallback.Create().After("gorm:create").Register("gorm:begin_reconnect", performReconnect)
+	DefaultCallback.Update().After("gorm:update").Register("gorm:begin_reconnect", performReconnect)
+	DefaultCallback.Delete().After("gorm:delete").Register("gorm:begin_reconnect", performReconnect)
+	DefaultCallback.Query().After("gorm:query").Register("gorm:begin_reconnect", performReconnect)
+}
+
+//May be do some kind of settings?
+const reconnectAttempts = 5
+const reconnectInterval = 5 * time.Second
+
+//performReconnect the callback used to peform some reconnect attempts in case of disconnect
+func performReconnect(scope *Scope) {
+	if scope.HasError() {
+
+		scope.db.reconnectGuard.Add(1)
+		defer scope.db.reconnectGuard.Done()
+
+		err := scope.db.Error
+
+		if scope.db.dialect.IsDisconnectError(err) {
+			for i := 0; i < reconnectAttempts; i++ {
+				newDb, openErr := Open(scope.db.dialectName, scope.db.dialectArgs...)
+				if openErr == nil {
+					oldDb := scope.db
+					if oldDb.parent != oldDb {
+						//In case of cloned db try to fix parents
+						//It is thread safe as we share mutex between instances
+						fixParentDbs(oldDb, newDb)
+					}
+					*scope.db = *newDb
+					break
+				} else {
+					//wait for interval and try to reconnect again
+					<-time.After(reconnectInterval)
+				}
+			}
+		}
+	}
+}
+
+func fixParentDbs(current, newDb *DB) {
+	iterator := current
+	parent := current.parent
+
+	for {
+		oldParent := parent
+		*parent = *newDb
+		parent = oldParent.parent
+		iterator = oldParent
+		if iterator == parent {
+			break
+		}
+	}
+}

callback_row_query.go

@@ -18,6 +18,8 @@ type RowsQueryResult struct {
 
 // queryCallback used to query data from database
 func rowQueryCallback(scope *Scope) {
+	scope.db.reconnectGuard.Wait()
+
 	if result, ok := scope.InstanceGet("row_query_result"); ok {
 		scope.prepareQuerySQL()
 

callback_update.go

@@ -56,6 +56,8 @@ func updateTimeStampForUpdateCallback(scope *Scope) {
 // updateCallback the callback used to update data to database
 func updateCallback(scope *Scope) {
 	if !scope.HasError() {
+		scope.db.reconnectGuard.Wait()
+
 		var sqls []string
 
 		if updateAttrs, ok := scope.InstanceGet("gorm:update_attrs"); ok {

dialect.go

@@ -46,6 +46,9 @@ type Dialect interface {
 
 	// CurrentDatabase return current database name
 	CurrentDatabase() string
+
+	//
+	IsDisconnectError(err error) bool
 }
 
 var dialectsMap = map[string]Dialect{}

dialect_common.go

@@ -1,6 +1,7 @@
 package gorm
 
 import (
+	"database/sql/driver"
 	"fmt"
 	"reflect"
 	"regexp"
@@ -21,7 +22,9 @@ type commonDialect struct {
 func init() {
 	RegisterDialect("common", &commonDialect{})
 }
-
+func (commonDialect) IsDisconnectError(err error) bool {
+	return err == driver.ErrBadConn
+}
 func (commonDialect) GetName() string {
 	return "common"
 }

dialect_mysql.go

@@ -2,7 +2,9 @@ package gorm
 
 import (
 	"crypto/sha1"
+	"database/sql/driver"
 	"fmt"
+	"github.com/go-sql-driver/mysql"
 	"reflect"
 	"regexp"
 	"strconv"
@@ -11,24 +13,28 @@ import (
 	"unicode/utf8"
 )
 
-type mysql struct {
+type mysqlDialect struct {
 	commonDialect
 }
 
 func init() {
-	RegisterDialect("mysql", &mysql{})
+	RegisterDialect("mysql", &mysqlDialect{})
 }
 
-func (mysql) GetName() string {
+func (mysqlDialect) IsDisconnectError(err error) bool {
+	return err == mysql.ErrInvalidConn || err == driver.ErrBadConn
+}
+
+func (mysqlDialect) GetName() string {
 	return "mysql"
 }
 
-func (mysql) Quote(key string) string {
+func (mysqlDialect) Quote(key string) string {
 	return fmt.Sprintf("`%s`", key)
 }
 
 // Get Data Type for MySQL Dialect
-func (s *mysql) DataTypeOf(field *StructField) string {
+func (s *mysqlDialect) DataTypeOf(field *StructField) string {
 	var dataValue, sqlType, size, additionalType = ParseFieldStructForDialect(field, s)
 
 	// MySQL allows only one auto increment column per table, and it must
@@ -122,12 +128,12 @@ func (s *mysql) DataTypeOf(field *StructField) string {
 	return fmt.Sprintf("%v %v", sqlType, additionalType)
 }
 
-func (s mysql) RemoveIndex(tableName string, indexName string) error {
+func (s mysqlDialect) RemoveIndex(tableName string, indexName string) error {
 	_, err := s.db.Exec(fmt.Sprintf("DROP INDEX %v ON %v", indexName, s.Quote(tableName)))
 	return err
 }
 
-func (s mysql) LimitAndOffsetSQL(limit, offset interface{}) (sql string) {
+func (s mysqlDialect) LimitAndOffsetSQL(limit, offset interface{}) (sql string) {
 	if limit != nil {
 		if parsedLimit, err := strconv.ParseInt(fmt.Sprint(limit), 0, 0); err == nil && parsedLimit >= 0 {
 			sql += fmt.Sprintf(" LIMIT %d", parsedLimit)
@@ -142,22 +148,22 @@ func (s mysql) LimitAndOffsetSQL(limit, offset interface{}) (sql string) {
 	return
 }
 
-func (s mysql) HasForeignKey(tableName string, foreignKeyName string) bool {
+func (s mysqlDialect) HasForeignKey(tableName string, foreignKeyName string) bool {
 	var count int
 	s.db.QueryRow("SELECT count(*) FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS WHERE CONSTRAINT_SCHEMA=? AND TABLE_NAME=? AND CONSTRAINT_NAME=? AND CONSTRAINT_TYPE='FOREIGN KEY'", s.CurrentDatabase(), tableName, foreignKeyName).Scan(&count)
 	return count > 0
 }
 
-func (s mysql) CurrentDatabase() (name string) {
+func (s mysqlDialect) CurrentDatabase() (name string) {
 	s.db.QueryRow("SELECT DATABASE()").Scan(&name)
 	return
 }
 
-func (mysql) SelectFromDummyTable() string {
+func (mysqlDialect) SelectFromDummyTable() string {
 	return "FROM DUAL"
 }
 
-func (s mysql) BuildForeignKeyName(tableName, field, dest string) string {
+func (s mysqlDialect) BuildForeignKeyName(tableName, field, dest string) string {
 	keyName := s.commonDialect.BuildForeignKeyName(tableName, field, dest)
 	if utf8.RuneCountInString(keyName) <= 64 {
 		return keyName

dialect_postgres.go

@@ -1,6 +1,7 @@
 package gorm
 
 import (
+	"database/sql/driver"
 	"fmt"
 	"reflect"
 	"strings"
@@ -19,6 +20,9 @@ func init() {
 func (postgres) GetName() string {
 	return "postgres"
 }
+func (postgres) IsDisconnectError(err error) bool {
+	return err == driver.ErrBadConn
+}
 
 func (postgres) BindVar(i int) string {
 	return fmt.Sprintf("$%v", i)

dialect_sqlite3.go

@@ -14,7 +14,10 @@ type sqlite3 struct {
 func init() {
 	RegisterDialect("sqlite3", &sqlite3{})
 }
-
+func (sqlite3) IsDisconnectError(err error) bool {
+	//sqlite is a file db so i think no reconnect needed or it is possible to treat file errors as disconnect
+	return false
+}
 func (sqlite3) GetName() string {
 	return "sqlite3"
 }

dialects/postgres/postgres.go

@@ -4,11 +4,11 @@ import (
 	"database/sql"
 	"database/sql/driver"
 
-	_ "github.com/lib/pq"
-	"github.com/lib/pq/hstore"
 	"encoding/json"
 	"errors"
 	"fmt"
+	_ "github.com/lib/pq"
+	"github.com/lib/pq/hstore"
 )
 
 type Hstore map[string]*string

main.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"reflect"
 	"strings"
+	"sync"
 	"time"
 )
 
@@ -22,7 +23,11 @@ type DB struct {
 	logger            logger
 	search            *search
 	values            map[string]interface{}
-
+	//Mutex to block all operations during reconnection
+	reconnectGuard *sync.WaitGroup
+	//connection string passed to Open saved for reconnect
+	dialectName string
+	dialectArgs []interface{}
 	// global db
 	parent        *DB
 	callbacks     *Callback
@@ -64,11 +69,14 @@ func Open(dialect string, args ...interface{}) (db *DB, err error) {
 	}
 
 	db = &DB{
-		db:        dbSQL,
-		logger:    defaultLogger,
-		values:    map[string]interface{}{},
-		callbacks: DefaultCallback,
-		dialect:   newDialect(dialect, dbSQL),
+		db:             dbSQL,
+		logger:         defaultLogger,
+		values:         map[string]interface{}{},
+		callbacks:      DefaultCallback,
+		dialect:        newDialect(dialect, dbSQL),
+		reconnectGuard: &sync.WaitGroup{},
+		dialectArgs:    args,
+		dialectName:    dialect,
 	}
 	db.parent = db
 	if err != nil {
@@ -712,11 +720,15 @@ func (s *DB) GetErrors() []error {
 
 func (s *DB) clone() *DB {
 	db := &DB{
-		db:                s.db,
-		parent:            s.parent,
-		logger:            s.logger,
-		logMode:           s.logMode,
-		values:            map[string]interface{}{},
+		db:      s.db,
+		parent:  s.parent,
+		logger:  s.logger,
+		logMode: s.logMode,
+		values:  map[string]interface{}{},
+		//share reconnection info with new copy
+		reconnectGuard:    s.reconnectGuard,
+		dialectName:       s.dialectName,
+		dialectArgs:       s.dialectArgs,
 		Value:             s.Value,
 		Error:             s.Error,
 		blockGlobalUpdate: s.blockGlobalUpdate,