diff --git a/engine.go b/engine.go
index 5fccf6c1..9e7053ab 100644
--- a/engine.go
+++ b/engine.go
@@ -47,6 +47,8 @@ type Engine struct {
 	disableGlobalCache bool
 
 	tagHandlers map[string]tagHandler
+
+	engineGroup *EngineGroup
 }
 
 // ShowSQL show SQL statement or not on logger if log level is great than INFO
diff --git a/engine_group.go b/engine_group.go
index 88d0db0f..dd1e6380 100644
--- a/engine_group.go
+++ b/engine_group.go
@@ -5,122 +5,88 @@
 package xorm
 
 import (
-	"database/sql"
-	"io"
-	"reflect"
 	"strings"
 	"time"
 
-	"github.com/go-xorm/builder"
 	"github.com/go-xorm/core"
 )
 
 type EngineGroup struct {
-	master  *Engine
-	slaves  []*Engine
-	weight  []int
-	count   int
-	s_count int
-	policy  GroupPolicy
-	p       int
+	*Engine
+	slaves []*Engine
+	policy GroupPolicy
 }
 
 func NewGroup(args1 interface{}, args2 interface{}, policies ...GroupPolicy) (*EngineGroup, error) {
-	var policy GroupPolicy
+	var eg EngineGroup
 	if len(policies) > 0 {
-		policy = policies[0]
+		eg.policy = policies[0]
 	} else {
-		policy = NewRandomPolicy()
+		eg.policy = NewRandomPolicy()
 	}
 
 	driverName, ok1 := args1.(string)
 	dataSourceNames, ok2 := args2.(string)
 	if ok1 && ok2 {
-		return newGroup1(driverName, dataSourceNames, policy)
+		conns := strings.Split(dataSourceNames, ";")
+		engines := make([]*Engine, len(conns))
+		for i, conn := range conns {
+			engine, err := NewEngine(driverName, conn)
+			if err != nil {
+				return nil, err
+			}
+			engine.engineGroup = &eg
+			engines[i] = engine
+		}
+
+		eg.Engine = engines[0]
+		eg.slaves = engines[1:]
+		return &eg, nil
 	}
 
-	Master, ok3 := args1.(*Engine)
-	Slaves, ok4 := args2.([]*Engine)
+	master, ok3 := args1.(*Engine)
+	slaves, ok4 := args2.([]*Engine)
 	if ok3 && ok4 {
-		return newGroup2(Master, Slaves, policy)
+		master.engineGroup = &eg
+		for i := 0; i < len(slaves); i++ {
+			slaves[i].engineGroup = &eg
+		}
+		return &eg, nil
 	}
 	return nil, ErrParamsType
 }
 
-func newGroup1(driverName string, dataSourceNames string, policy GroupPolicy) (*EngineGroup, error) {
-	conns := strings.Split(dataSourceNames, ";")
-	engines := make([]*Engine, len(conns))
-	for i, _ := range conns {
-		engine, err := NewEngine(driverName, conns[i])
-		if err != nil {
-			return nil, err
-		}
-		engines[i] = engine
-	}
-
-	return &EngineGroup{
-		master:  engines[0],
-		slaves:  engines[1:],
-		count:   len(engines),
-		s_count: len(engines[1:]),
-		policy:  policy,
-	}, nil
-}
-
-func newGroup2(Master *Engine, Slaves []*Engine, policy GroupPolicy) (*EngineGroup, error) {
-	return &EngineGroup{
-		master:  Master,
-		slaves:  Slaves,
-		count:   1 + len(Slaves),
-		s_count: len(Slaves),
-		policy:  policy,
-	}, nil
-}
-
 func (eg *EngineGroup) SetPolicy(policy GroupPolicy) *EngineGroup {
 	eg.policy = policy
 	return eg
 }
 
 func (eg *EngineGroup) Master() *Engine {
-	return eg.master
+	return eg.Engine
 }
 
 // Slave returns one of the physical databases which is a slave
 func (eg *EngineGroup) Slave() *Engine {
-	if eg.count == 1 {
-		return eg.master
+	switch len(eg.slaves) {
+	case 0:
+		return eg.Engine
+	case 1:
+		return eg.slaves[0]
 	}
 	return eg.policy.Slave(eg)
 }
 
 func (eg *EngineGroup) Slaves() []*Engine {
-	if eg.count == 1 {
-		return []*Engine{eg.master}
-	}
 	return eg.slaves
 }
 
 func (eg *EngineGroup) GetSlave(i int) *Engine {
-	if eg.count == 1 || i == 0 {
-		return eg.master
-	}
-	if i > eg.s_count {
-		return eg.slaves[0]
-	}
 	return eg.slaves[i]
 }
 
-func (eg *EngineGroup) GetEngine(i int) *Engine {
-	if i >= eg.count || i == 0 {
-		return eg.master
-	}
-	return eg.slaves[i-1]
-}
-
 // ShowSQL show SQL statement or not on logger if log level is great than INFO
 func (eg *EngineGroup) ShowSQL(show ...bool) {
-	eg.master.ShowSQL(show...)
+	eg.Engine.ShowSQL(show...)
 	for i, _ := range eg.slaves {
 		eg.slaves[i].ShowSQL(show...)
 	}
@@ -128,7 +94,7 @@ func (eg *EngineGroup) ShowSQL(show ...bool) {
 
 // ShowExecTime show SQL statement and execute time or not on logger if log level is great than INFO
 func (eg *EngineGroup) ShowExecTime(show ...bool) {
-	eg.master.ShowExecTime(show...)
+	eg.Engine.ShowExecTime(show...)
 	for i, _ := range eg.slaves {
 		eg.slaves[i].ShowExecTime(show...)
 	}
@@ -136,8 +102,8 @@ func (eg *EngineGroup) ShowExecTime(show ...bool) {
 
 // SetMapper set the name mapping rules
 func (eg *EngineGroup) SetMapper(mapper core.IMapper) {
-	eg.master.SetTableMapper(mapper)
-	eg.master.SetColumnMapper(mapper)
+	eg.Engine.SetTableMapper(mapper)
+	eg.Engine.SetColumnMapper(mapper)
 	for i, _ := range eg.slaves {
 		eg.slaves[i].SetTableMapper(mapper)
 		eg.slaves[i].SetColumnMapper(mapper)
@@ -146,7 +112,7 @@ func (eg *EngineGroup) SetMapper(mapper core.IMapper) {
 
 // SetTableMapper set the table name mapping rule
 func (eg *EngineGroup) SetTableMapper(mapper core.IMapper) {
-	eg.master.TableMapper = mapper
+	eg.Engine.TableMapper = mapper
 	for i, _ := range eg.slaves {
 		eg.slaves[i].TableMapper = mapper
 	}
@@ -154,7 +120,7 @@ func (eg *EngineGroup) SetTableMapper(mapper core.IMapper) {
 
 // SetColumnMapper set the column name mapping rule
 func (eg *EngineGroup) SetColumnMapper(mapper core.IMapper) {
-	eg.master.ColumnMapper = mapper
+	eg.Engine.ColumnMapper = mapper
 	for i, _ := range eg.slaves {
 		eg.slaves[i].ColumnMapper = mapper
 	}
@@ -162,7 +128,7 @@ func (eg *EngineGroup) SetColumnMapper(mapper core.IMapper) {
 
 // SetMaxOpenConns is only available for go 1.2+
 func (eg *EngineGroup) SetMaxOpenConns(conns int) {
-	eg.master.db.SetMaxOpenConns(conns)
+	eg.Engine.db.SetMaxOpenConns(conns)
 	for i, _ := range eg.slaves {
 		eg.slaves[i].db.SetMaxOpenConns(conns)
 	}
@@ -170,21 +136,15 @@ func (eg *EngineGroup) SetMaxOpenConns(conns int) {
 
 // SetMaxIdleConns set the max idle connections on pool, default is 2
 func (eg *EngineGroup) SetMaxIdleConns(conns int) {
-	eg.master.db.SetMaxIdleConns(conns)
+	eg.Engine.db.SetMaxIdleConns(conns)
 	for i, _ := range eg.slaves {
 		eg.slaves[i].db.SetMaxIdleConns(conns)
 	}
 }
 
-// NoCascade If you do not want to auto cascade load object
-func (eg *EngineGroup) NoCascade() *EGSession {
-	egs := eg.NewEGSession()
-	return egs.NoCascade()
-}
-
 // Close the engine
 func (eg *EngineGroup) Close() error {
-	err := eg.master.db.Close()
+	err := eg.Engine.db.Close()
 	if err != nil {
 		return err
 	}
@@ -200,630 +160,22 @@ func (eg *EngineGroup) Close() error {
 
 // Ping tests if database is alive
 func (eg *EngineGroup) Ping() error {
-	eg.master.Ping()
-	return scatter(eg.s_count, func(i int) error {
-		return eg.slaves[i].Ping()
-	})
+	if err := eg.Engine.Ping(); err != nil {
+		return err
+	}
+
+	for _, slave := range eg.slaves {
+		if err := slave.Ping(); err != nil {
+			return err
+		}
+	}
+	return nil
 }
 
 // SetConnMaxLifetime sets the maximum amount of time a connection may be reused.
 func (eg *EngineGroup) SetConnMaxLifetime(d time.Duration) {
-	eg.master.db.SetConnMaxLifetime(d)
+	eg.Engine.db.SetConnMaxLifetime(d)
 	for i, _ := range eg.slaves {
 		eg.slaves[i].db.SetConnMaxLifetime(d)
 	}
 }
-
-func scatter(n int, fn func(i int) error) error {
-	errors := make(chan error, n)
-
-	var i int
-	for i = 0; i < n; i++ {
-		go func(i int) { errors <- fn(i) }(i)
-	}
-
-	var err, innerErr error
-	for i = 0; i < cap(errors); i++ {
-		if innerErr = <-errors; innerErr != nil {
-			err = innerErr
-		}
-	}
-
-	return err
-}
-
-// SqlType will be deprecated, please use SQLType instead
-//
-// Deprecated: use SQLType instead
-func (eg *EngineGroup) SqlType(c *core.Column) string {
-	return eg.Master().SQLType(c)
-}
-
-// SQLType A simple wrapper to dialect's core.SqlType method
-func (eg *EngineGroup) SQLType(c *core.Column) string {
-	return eg.Master().dialect.SqlType(c)
-}
-
-// NewSession New a session
-func (eg *EngineGroup) NewSession() *Session {
-	return eg.Master().NewSession()
-}
-
-// NewSession New a session
-func (eg *EngineGroup) NewEGSession() *EGSession {
-	args := make(map[string]interface{})
-	egs := &EGSession{eg: eg, operation: []string{}, args: args}
-	return egs
-}
-
-type SqlArgs struct {
-	query string
-	args  []interface{}
-}
-
-func (eg *EngineGroup) Sql(query string, args ...interface{}) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.Sql(query, args...)
-}
-
-func (eg *EngineGroup) SQL(query interface{}, args ...interface{}) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.SQL(query, args...)
-}
-
-// NoAutoTime Default if your struct has "created" or "updated" filed tag, the fields
-// will automatically be filled with current time when Insert or Update
-// invoked. Call NoAutoTime if you dont' want to fill automatically.
-func (eg *EngineGroup) NoAutoTime() *EGSession {
-	egs := eg.NewEGSession()
-	return egs.NoAutoTime()
-}
-
-type NoAutoConditionArgs struct {
-	no []bool
-}
-
-// NoAutoCondition disable auto generate Where condition from bean or not
-func (eg *EngineGroup) NoAutoCondition(no ...bool) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.NoAutoCondition(no...)
-}
-
-// DBMetas Retrieve all tables, columns, indexes' informations from database.
-func (eg *EngineGroup) DBMetas() ([]*core.Table, error) {
-	return eg.Master().DBMetas()
-}
-
-// DumpAllToFile dump database all table structs and data to a file
-func (eg *EngineGroup) DumpAllToFile(fp string, tp ...core.DbType) error {
-	return eg.Master().DumpAllToFile(fp, tp...)
-}
-
-// DumpAll dump database all table structs and data to w
-func (eg *EngineGroup) DumpAll(w io.Writer, tp ...core.DbType) error {
-	return eg.Master().DumpAll(w, tp...)
-}
-
-// DumpTablesToFile dump specified tables to SQL file.
-func (eg *EngineGroup) DumpTablesToFile(tables []*core.Table, fp string, tp ...core.DbType) error {
-	return eg.Master().DumpTablesToFile(tables, fp, tp...)
-}
-
-// DumpTables dump specify tables to io.Writer
-func (eg *EngineGroup) DumpTables(tables []*core.Table, w io.Writer, tp ...core.DbType) error {
-	return eg.Master().DumpTables(tables, w, tp...)
-}
-
-type CascadeArgs struct {
-	trueOrFalse []bool
-}
-
-// Cascade use cascade or not
-func (eg *EngineGroup) Cascade(trueOrFalse ...bool) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.Cascade(trueOrFalse...)
-}
-
-type WhereArgs struct {
-	query interface{}
-	args  []interface{}
-}
-
-// Where method provide a condition query
-func (eg *EngineGroup) Where(query interface{}, args ...interface{}) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.Where(query, args...)
-}
-
-type IdArgs struct {
-	id interface{}
-}
-
-// Id will be deprecated, please use ID instead
-func (eg *EngineGroup) Id(id interface{}) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.Id(id)
-}
-
-type IDArgs struct {
-	id interface{}
-}
-
-// ID method provoide a condition as (id) = ?
-func (eg *EngineGroup) ID(id interface{}) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.ID(id)
-}
-
-type BeforeArgs struct {
-	closures func(interface{})
-}
-
-// Before apply before Processor, affected bean is passed to closure arg
-func (eg *EngineGroup) Before(closures func(interface{})) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.Before(closures)
-}
-
-type AfterArgs struct {
-	closures func(interface{})
-}
-
-// After apply after insert Processor, affected bean is passed to closure arg
-func (eg *EngineGroup) After(closures func(interface{})) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.After(closures)
-}
-
-type CharsetArgs struct {
-	charset string
-}
-
-// Charset set charset when create table, only support mysql now
-func (eg *EngineGroup) Charset(charset string) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.Charset(charset)
-}
-
-type StoreEngineArgs struct {
-	storeEngine string
-}
-
-// StoreEngine set store engine when create table, only support mysql now
-func (eg *EngineGroup) StoreEngine(storeEngine string) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.StoreEngine(storeEngine)
-}
-
-type DistinctArgs struct {
-	columns []string
-}
-
-// Distinct use for distinct columns. Caution: when you are using cache,
-// distinct will not be cached because cache system need id,
-// but distinct will not provide id
-func (eg *EngineGroup) Distinct(columns ...string) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.Distinct(columns...)
-}
-
-type SelectArgs struct {
-	str string
-}
-
-// Select customerize your select columns or contents
-func (eg *EngineGroup) Select(str string) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.Select(str)
-}
-
-type ColsArgs struct {
-	columns []string
-}
-
-// Cols only use the parameters as select or update columns
-func (eg *EngineGroup) Cols(columns ...string) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.Cols(columns...)
-}
-
-// AllCols indicates that all columns should be use
-func (eg *EngineGroup) AllCols() *EGSession {
-	egs := eg.NewEGSession()
-	return egs.AllCols()
-}
-
-type MustColsArgs struct {
-	columns []string
-}
-
-// MustCols specify some columns must use even if they are empty
-func (eg *EngineGroup) MustCols(columns ...string) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.MustCols(columns...)
-}
-
-type UseBoolArgs struct {
-	columns []string
-}
-
-// UseBool xorm automatically retrieve condition according struct, but
-// if struct has bool field, it will ignore them. So use UseBool
-// to tell system to do not ignore them.
-// If no parameters, it will use all the bool field of struct, or
-// it will use parameters's columns
-func (eg *EngineGroup) UseBool(columns ...string) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.UseBool(columns...)
-}
-
-type OmitArgs struct {
-	columns []string
-}
-
-// Omit only not use the parameters as select or update columns
-func (eg *EngineGroup) Omit(columns ...string) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.Omit(columns...)
-}
-
-type NullableArgs struct {
-	columns []string
-}
-
-// Nullable set null when column is zero-value and nullable for update
-func (eg *EngineGroup) Nullable(columns ...string) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.Nullable(columns...)
-}
-
-type InArgs struct {
-	column string
-	args   []interface{}
-}
-
-// In will generate "column IN (?, ?)"
-func (eg *EngineGroup) In(column string, args ...interface{}) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.In(column, args...)
-}
-
-type NotInArgs struct {
-	column string
-	args   []interface{}
-}
-
-// NotIn will generate "column NOT IN (?, ?)"
-func (eg *EngineGroup) NotIn(column string, args ...interface{}) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.NotIn(column, args...)
-}
-
-type IncrArgs struct {
-	column string
-	args   []interface{}
-}
-
-// Incr provides a update string like "column = column + ?"
-func (eg *EngineGroup) Incr(column string, args ...interface{}) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.Incr(column, args...)
-}
-
-type DecrArgs struct {
-	column string
-	args   []interface{}
-}
-
-// Decr provides a update string like "column = column - ?"
-func (eg *EngineGroup) Decr(column string, args ...interface{}) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.Decr(column, args...)
-}
-
-type SetExprArgs struct {
-	column     string
-	expression string
-}
-
-// SetExpr provides a update string like "column = {expression}"
-func (eg *EngineGroup) SetExpr(column string, expression string) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.SetExpr(column, expression)
-}
-
-type TableArgs struct {
-	tableNameOrBean interface{}
-}
-
-// Table temporarily change the Get, Find, Update's table
-func (eg *EngineGroup) Table(tableNameOrBean interface{}) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.Table(tableNameOrBean)
-}
-
-type AliasArgs struct {
-	alias string
-}
-
-// Alias set the table alias
-func (eg *EngineGroup) Alias(alias string) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.Alias(alias)
-}
-
-type LimitArgs struct {
-	limit int
-	start []int
-}
-
-// Limit will generate "LIMIT start, limit"
-func (eg *EngineGroup) Limit(limit int, start ...int) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.Limit(limit, start...)
-}
-
-type DescArgs struct {
-	colNames []string
-}
-
-// Desc will generate "ORDER BY column1 DESC, column2 DESC"
-func (eg *EngineGroup) Desc(colNames ...string) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.Desc(colNames...)
-}
-
-type AscArgs struct {
-	colNames []string
-}
-
-// Asc will generate "ORDER BY column1,column2 Asc"
-// This method can chainable use.
-//
-//        engine.Desc("name").Asc("age").Find(&users)
-//        // SELECT * FROM user ORDER BY name DESC, age ASC
-//
-func (eg *EngineGroup) Asc(colNames ...string) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.Asc(colNames...)
-}
-
-type OrderByArgs struct {
-	order string
-}
-
-// OrderBy will generate "ORDER BY order"
-func (eg *EngineGroup) OrderBy(order string) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.OrderBy(order)
-}
-
-type JoinArgs struct {
-	joinOperator string
-	tablename    interface{}
-	condition    string
-	args         []interface{}
-}
-
-// Join the join_operator should be one of INNER, LEFT OUTER, CROSS etc - this will be prepended to JOIN
-func (eg *EngineGroup) Join(joinOperator string, tablename interface{}, condition string, args ...interface{}) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.Join(joinOperator, tablename, condition, args...)
-}
-
-type GroupByArgs struct {
-	keys string
-}
-
-// GroupBy generate group by statement
-func (eg *EngineGroup) GroupBy(keys string) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.GroupBy(keys)
-}
-
-type HavingArgs struct {
-	conditions string
-}
-
-// Having generate having statement
-func (eg *EngineGroup) Having(conditions string) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.Having(conditions)
-}
-
-// IdOf get id from one struct
-//
-// Deprecated: use IDOf instead.
-func (eg *EngineGroup) IdOf(bean interface{}) core.PK {
-	return eg.Master().IdOf(bean)
-}
-
-// IDOf get id from one struct
-func (eg *EngineGroup) IDOf(bean interface{}) core.PK {
-	return eg.Master().IDOf(bean)
-}
-
-// IdOfV get id from one value of struct
-//
-// Deprecated: use IDOfV instead.
-func (eg *EngineGroup) IdOfV(rv reflect.Value) core.PK {
-	return eg.Master().IdOfV(rv)
-}
-
-// IDOfV get id from one value of struct
-func (eg *EngineGroup) IDOfV(rv reflect.Value) core.PK {
-	return eg.Master().IDOfV(rv)
-}
-
-// CreateIndexes create indexes
-func (eg *EngineGroup) CreateIndexes(bean interface{}) error {
-	return eg.Master().CreateIndexes(bean)
-}
-
-// CreateUniques create uniques
-func (eg *EngineGroup) CreateUniques(bean interface{}) error {
-	return eg.Master().CreateUniques(bean)
-}
-
-// Sync the new struct changes to database, this method will automatically add
-// table, column, index, unique. but will not delete or change anything.
-// If you change some field, you should change the database manually.
-func (eg *EngineGroup) Sync(beans ...interface{}) error {
-	return eg.Master().Sync(beans...)
-}
-
-// Sync2 synchronize structs to database tables
-func (eg *EngineGroup) Sync2(beans ...interface{}) error {
-	return eg.Master().Sync2(beans...)
-}
-
-// CreateTables create tabls according bean
-func (eg *EngineGroup) CreateTables(beans ...interface{}) error {
-	return eg.Master().CreateTables(beans...)
-}
-
-// DropTables drop specify tables
-func (eg *EngineGroup) DropTables(beans ...interface{}) error {
-	return eg.Master().DropTables(beans...)
-}
-
-// DropIndexes drop indexes of a table
-func (eg *EngineGroup) DropIndexes(bean interface{}) error {
-	return eg.Master().DropIndexes(bean)
-}
-
-func (eg *EngineGroup) Exec(sql string, args ...interface{}) (sql.Result, error) {
-	return eg.Master().Exec(sql, args...)
-}
-
-// Query a raw sql and return records as []map[string][]byte
-func (eg *EngineGroup) Query(sql string, paramStr ...interface{}) (resultsSlice []map[string][]byte, err error) {
-	return eg.Slave().Query(sql, paramStr...)
-}
-
-// QueryString runs a raw sql and return records as []map[string]string
-func (eg *EngineGroup) QueryString(sqlStr string, args ...interface{}) ([]map[string]string, error) {
-	return eg.Slave().QueryString(sqlStr, args...)
-}
-
-// QueryInterface runs a raw sql and return records as []map[string]interface{}
-func (eg *EngineGroup) QueryInterface(sqlStr string, args ...interface{}) ([]map[string]interface{}, error) {
-	return eg.Slave().QueryInterface(sqlStr, args...)
-}
-
-// Insert one or more records
-func (eg *EngineGroup) Insert(beans ...interface{}) (int64, error) {
-	return eg.Master().Insert(beans...)
-}
-
-// InsertOne insert only one record
-func (eg *EngineGroup) InsertOne(bean interface{}) (int64, error) {
-	return eg.Master().InsertOne(bean)
-}
-
-// IsTableEmpty if a table has any reocrd
-func (eg *EngineGroup) IsTableEmpty(bean interface{}) (bool, error) {
-	return eg.Master().IsTableEmpty(bean)
-}
-
-// IsTableExist if a table is exist
-func (eg *EngineGroup) IsTableExist(beanOrTableName interface{}) (bool, error) {
-	return eg.Master().IsTableExist(beanOrTableName)
-}
-
-func (eg *EngineGroup) Update(bean interface{}, condiBeans ...interface{}) (int64, error) {
-	return eg.Master().Update(bean, condiBeans...)
-}
-
-// Delete records, bean's non-empty fields are conditions
-func (eg *EngineGroup) Delete(bean interface{}) (int64, error) {
-	return eg.Master().Delete(bean)
-}
-
-// Get retrieve one record from table, bean's non-empty fields
-// are conditions
-func (eg *EngineGroup) Get(bean interface{}) (bool, error) {
-	return eg.Slave().Get(bean)
-}
-
-// Exist returns true if the record exist otherwise return false
-func (eg *EngineGroup) Exist(bean ...interface{}) (bool, error) {
-	return eg.Slave().Exist(bean...)
-}
-
-// Iterate record by record handle records from table, bean's non-empty fields
-// are conditions.
-func (eg *EngineGroup) Iterate(bean interface{}, fun IterFunc) error {
-	return eg.Master().Iterate(bean, fun)
-}
-
-func (eg *EngineGroup) Find(beans interface{}, condiBeans ...interface{}) error {
-	return eg.Slave().Find(beans, condiBeans...)
-}
-
-// Rows return sql.Rows compatible Rows obj, as a forward Iterator object for iterating record by record, bean's non-empty fields
-// are conditions.
-func (eg *EngineGroup) Rows(bean interface{}) (*Rows, error) {
-	return eg.Slave().Rows(bean)
-}
-
-// Count counts the records. bean's non-empty fields are conditions.
-func (eg *EngineGroup) Count(bean ...interface{}) (int64, error) {
-	return eg.Slave().Count(bean...)
-}
-
-// Sum sum the records by some column. bean's non-empty fields are conditions.
-func (eg *EngineGroup) Sum(bean interface{}, colName string) (float64, error) {
-	return eg.Slave().Sum(bean, colName)
-}
-
-// SumInt sum the records by some column. bean's non-empty fields are conditions.
-func (eg *EngineGroup) SumInt(bean interface{}, colName string) (int64, error) {
-	return eg.Slave().SumInt(bean, colName)
-}
-
-// Sums sum the records by some columns. bean's non-empty fields are conditions.
-func (eg *EngineGroup) Sums(bean interface{}, colNames ...string) ([]float64, error) {
-	return eg.Slave().Sums(bean, colNames...)
-}
-
-// SumsInt like Sums but return slice of int64 instead of float64.
-func (eg *EngineGroup) SumsInt(bean interface{}, colNames ...string) ([]int64, error) {
-	return eg.Slave().SumsInt(bean, colNames...)
-}
-
-// ImportFile SQL DDL file
-func (eg *EngineGroup) ImportFile(ddlPath string) ([]sql.Result, error) {
-	return eg.Master().ImportFile(ddlPath)
-}
-
-// Import SQL DDL from io.Reader
-func (eg *EngineGroup) Import(r io.Reader) ([]sql.Result, error) {
-	return eg.Master().Import(r)
-}
-
-// NowTime2 return current time
-func (eg *EngineGroup) NowTime2(sqlTypeName string) (interface{}, time.Time) {
-	return eg.Master().NowTime2(sqlTypeName)
-}
-
-// Unscoped always disable struct tag "deleted"
-func (eg *EngineGroup) Unscoped() *EGSession {
-	egs := eg.NewEGSession()
-	return egs.Unscoped()
-}
-
-// CondDeleted returns the conditions whether a record is soft deleted.
-func (eg *EngineGroup) CondDeleted(colName string) builder.Cond {
-	return eg.Master().CondDeleted(colName)
-}
-
-type BufferSizeArgs struct {
-	size int
-}
-
-// BufferSize sets buffer size for iterate
-func (eg *EngineGroup) BufferSize(size int) *EGSession {
-	egs := eg.NewEGSession()
-	return egs.BufferSize(size)
-}
diff --git a/engine_group_session.go b/engine_group_session.go
deleted file mode 100644
index 0f333cb1..00000000
--- a/engine_group_session.go
+++ /dev/null
@@ -1,764 +0,0 @@
-package xorm
-
-import (
-	"database/sql"
-
-	"github.com/go-xorm/builder"
-)
-
-type EGSession struct {
-	eg        *EngineGroup
-	operation []string
-	args      map[string]interface{}
-	err       error
-}
-
-func (egs *EGSession) operate(session *Session) *Session {
-	for _, v := range egs.operation {
-		switch v {
-		case "Before":
-			args := egs.args["Before"].(BeforeArgs)
-			session = session.Before(args.closures)
-		case "After":
-			args := egs.args["After"].(AfterArgs)
-			session = session.After(args.closures)
-		case "Table":
-			args := egs.args["Table"].(TableArgs)
-			session = session.Table(args.tableNameOrBean)
-		case "Alias":
-			args := egs.args["Alias"].(AliasArgs)
-			session = session.Alias(args.alias)
-		case "NoCascade":
-			session = session.NoCascade()
-		case "ForUpdate":
-			session = session.ForUpdate()
-		case "NoAutoCondition":
-			args := egs.args["NoAutoCondition"].(NoAutoConditionArgs)
-			session = session.NoAutoCondition(args.no...)
-		case "Limit":
-			args := egs.args["Limit"].(LimitArgs)
-			session = session.Limit(args.limit, args.start...)
-		case "OrderBy":
-			args := egs.args["OrderBy"].(OrderByArgs)
-			session = session.OrderBy(args.order)
-		case "Desc":
-			args := egs.args["Desc"].(DescArgs)
-			session = session.Desc(args.colNames...)
-		case "Asc":
-			args := egs.args["Asc"].(AscArgs)
-			session = session.Asc(args.colNames...)
-		case "StoreEngine":
-			args := egs.args["StoreEngine"].(StoreEngineArgs)
-			session = session.StoreEngine(args.storeEngine)
-		case "Charset":
-			args := egs.args["Charset"].(CharsetArgs)
-			session = session.Charset(args.charset)
-		case "Cascade":
-			args := egs.args["Cascade"].(CascadeArgs)
-			session = session.Cascade(args.trueOrFalse...)
-		case "NoCache":
-			session = session.NoCache()
-		case "Join":
-			args := egs.args["Join"].(JoinArgs)
-			session = session.Join(args.joinOperator, args.tablename, args.condition, args.args...)
-		case "GroupBy":
-			args := egs.args["GroupBy"].(GroupByArgs)
-			session = session.GroupBy(args.keys)
-		case "Having":
-			args := egs.args["Having"].(HavingArgs)
-			session = session.Having(args.conditions)
-		case "Unscoped":
-			session = session.Unscoped()
-		case "Incr":
-			args := egs.args["Incr"].(IncrArgs)
-			session = session.Incr(args.column, args.args...)
-		case "Decr":
-			args := egs.args["Decr"].(DecrArgs)
-			session = session.Decr(args.column, args.args...)
-		case "SetExpr":
-			args := egs.args["SetExpr"].(SetExprArgs)
-			session = session.SetExpr(args.column, args.expression)
-		case "Select":
-			args := egs.args["Select"].(SelectArgs)
-			session = session.Select(args.str)
-		case "Cols":
-			args := egs.args["Cols"].(ColsArgs)
-			session = session.Cols(args.columns...)
-		case "AllCols":
-			session = session.AllCols()
-		case "MustCols":
-			args := egs.args["MustCols"].(MustColsArgs)
-			session = session.MustCols(args.columns...)
-		case "UseBool":
-			args := egs.args["UseBool"].(UseBoolArgs)
-			session = session.UseBool(args.columns...)
-		case "Distinct":
-			args := egs.args["Distinct"].(DistinctArgs)
-			session = session.Distinct(args.columns...)
-		case "Omit":
-			args := egs.args["Omit"].(OmitArgs)
-			session = session.Omit(args.columns...)
-		case "Nullable":
-			args := egs.args["Nullable"].(NullableArgs)
-			session = session.Nullable(args.columns...)
-		case "NoAutoTime":
-			session = session.NoAutoTime()
-		case "Sql":
-			args := egs.args["Sql"].(SqlArgs)
-			session = session.Sql(args.query, args.args...)
-		case "SQL":
-			args := egs.args["SQL"].(SqlArgs)
-			session = session.SQL(args.query, args.args...)
-		case "Where":
-			args := egs.args["Where"].(WhereArgs)
-			session = session.Where(args.query, args.args...)
-		case "And":
-			args := egs.args["And"].(AndArgs)
-			session = session.And(args.query, args.args...)
-		case "Or":
-			args := egs.args["Or"].(OrArgs)
-			session = session.Or(args.query, args.args...)
-		case "Id":
-			args := egs.args["Id"].(IdArgs)
-			session = session.Id(args.id)
-		case "ID":
-			args := egs.args["ID"].(IDArgs)
-			session = session.ID(args.id)
-		case "In":
-			args := egs.args["In"].(InArgs)
-			session = session.In(args.column, args.args...)
-		case "NotIn":
-			args := egs.args["NotIn"].(NotInArgs)
-			session = session.NotIn(args.column, args.args...)
-		case "BufferSize":
-			args := egs.args["BufferSize"].(BufferSizeArgs)
-			session = session.BufferSize(args.size)
-		}
-	}
-	return session
-}
-
-// Before Apply before Processor, affected bean is passed to closure arg
-func (egs *EGSession) Before(closures func(interface{})) *EGSession {
-	egs.operation = append(egs.operation, "Before")
-	args := BeforeArgs{
-		closures: closures,
-	}
-	egs.args["Before"] = args
-	return egs
-}
-
-// After Apply after Processor, affected bean is passed to closure arg
-func (egs *EGSession) After(closures func(interface{})) *EGSession {
-	egs.operation = append(egs.operation, "After")
-	args := AfterArgs{
-		closures: closures,
-	}
-	egs.args["After"] = args
-	return egs
-}
-
-// Table can input a string or pointer to struct for special a table to operate.
-func (egs *EGSession) Table(tableNameOrBean interface{}) *EGSession {
-	egs.operation = append(egs.operation, "Table")
-	args := TableArgs{
-		tableNameOrBean: tableNameOrBean,
-	}
-	egs.args["Table"] = args
-	return egs
-}
-
-// Alias set the table alias
-func (egs *EGSession) Alias(alias string) *EGSession {
-	egs.operation = append(egs.operation, "Alias")
-	args := AliasArgs{
-		alias: alias,
-	}
-	egs.args["Alias"] = args
-	return egs
-}
-
-// NoCascade indicate that no cascade load child object
-func (egs *EGSession) NoCascade() *EGSession {
-	egs.operation = append(egs.operation, "NoCascade")
-	return egs
-}
-
-// ForUpdate Set Read/Write locking for UPDATE
-func (egs *EGSession) ForUpdate() *EGSession {
-	egs.operation = append(egs.operation, "ForUpdate")
-	return egs
-}
-
-// NoAutoCondition disable generate SQL condition from beans
-func (egs *EGSession) NoAutoCondition(no ...bool) *EGSession {
-	egs.operation = append(egs.operation, "NoAutoCondition")
-	args := NoAutoConditionArgs{
-		no: no,
-	}
-	egs.args["NoAutoCondition"] = args
-	return egs
-}
-
-// Limit provide limit and offset query condition
-func (egs *EGSession) Limit(limit int, start ...int) *EGSession {
-	egs.operation = append(egs.operation, "Limit")
-	args := LimitArgs{
-		limit: limit,
-		start: start,
-	}
-	egs.args["Limit"] = args
-	return egs
-}
-
-// OrderBy provide order by query condition, the input parameter is the content
-// after order by on a sql statement.
-func (egs *EGSession) OrderBy(order string) *EGSession {
-	egs.operation = append(egs.operation, "OrderBy")
-	args := OrderByArgs{
-		order: order,
-	}
-	egs.args["OrderBy"] = args
-	return egs
-}
-
-// Desc provide desc order by query condition, the input parameters are columns.
-func (egs *EGSession) Desc(colNames ...string) *EGSession {
-	egs.operation = append(egs.operation, "Desc")
-	args := DescArgs{
-		colNames: colNames,
-	}
-	egs.args["Desc"] = args
-	return egs
-}
-
-// Asc provide asc order by query condition, the input parameters are columns.
-func (egs *EGSession) Asc(colNames ...string) *EGSession {
-	egs.operation = append(egs.operation, "Asc")
-	args := AscArgs{
-		colNames: colNames,
-	}
-	egs.args["Asc"] = args
-	return egs
-}
-
-// StoreEngine is only avialble mysql dialect currently
-func (egs *EGSession) StoreEngine(storeEngine string) *EGSession {
-	egs.operation = append(egs.operation, "StoreEngine")
-	args := StoreEngineArgs{
-		storeEngine: storeEngine,
-	}
-	egs.args["StoreEngine"] = args
-	return egs
-}
-
-// Charset is only avialble mysql dialect currently
-func (egs *EGSession) Charset(charset string) *EGSession {
-	egs.operation = append(egs.operation, "Charset")
-	args := CharsetArgs{
-		charset: charset,
-	}
-	egs.args["Charset"] = args
-	return egs
-}
-
-// Cascade indicates if loading sub Struct
-func (egs *EGSession) Cascade(trueOrFalse ...bool) *EGSession {
-	egs.operation = append(egs.operation, "Cascade")
-	args := CascadeArgs{
-		trueOrFalse: trueOrFalse,
-	}
-	egs.args["Cascade"] = args
-	return egs
-}
-
-// NoCache ask this session do not retrieve data from cache system and
-// get data from database directly.
-func (egs *EGSession) NoCache() *EGSession {
-	egs.operation = append(egs.operation, "NoCache")
-	return egs
-}
-
-// Join join_operator should be one of INNER, LEFT OUTER, CROSS etc - this will be prepended to JOIN
-func (egs *EGSession) Join(joinOperator string, tablename interface{}, condition string, args ...interface{}) *EGSession {
-	egs.operation = append(egs.operation, "Join")
-	joinArgs := JoinArgs{
-		joinOperator: joinOperator,
-		tablename:    tablename,
-		condition:    condition,
-		args:         args,
-	}
-	egs.args["Join"] = joinArgs
-	return egs
-}
-
-// GroupBy Generate Group By statement
-func (egs *EGSession) GroupBy(keys string) *EGSession {
-	egs.operation = append(egs.operation, "GroupBy")
-	args := GroupByArgs{
-		keys: keys,
-	}
-	egs.args["GroupBy"] = args
-	return egs
-}
-
-// Having Generate Having statement
-func (egs *EGSession) Having(conditions string) *EGSession {
-	egs.operation = append(egs.operation, "Having")
-	args := HavingArgs{
-		conditions: conditions,
-	}
-	egs.args["Having"] = args
-	return egs
-}
-
-// Unscoped always disable struct tag "deleted"
-func (egs *EGSession) Unscoped() *EGSession {
-	egs.operation = append(egs.operation, "Unscoped")
-	return egs
-}
-
-// Incr provides a query string like "count = count + 1"
-func (egs *EGSession) Incr(column string, args ...interface{}) *EGSession {
-	egs.operation = append(egs.operation, "Incr")
-	incrArgs := IncrArgs{
-		column: column,
-		args:   args,
-	}
-	egs.args["Incr"] = incrArgs
-	return egs
-}
-
-// Decr provides a query string like "count = count - 1"
-func (egs *EGSession) Decr(column string, args ...interface{}) *EGSession {
-	egs.operation = append(egs.operation, "Decr")
-	decrArgs := DecrArgs{
-		column: column,
-		args:   args,
-	}
-	egs.args["Decr"] = decrArgs
-	return egs
-}
-
-// SetExpr provides a query string like "column = {expression}"
-func (egs *EGSession) SetExpr(column string, expression string) *EGSession {
-	egs.operation = append(egs.operation, "SetExpr")
-	args := SetExprArgs{
-		column:     column,
-		expression: expression,
-	}
-	egs.args["SetExpr"] = args
-	return egs
-}
-
-// Select provides some columns to special
-func (egs *EGSession) Select(str string) *EGSession {
-	egs.operation = append(egs.operation, "Select")
-	args := SelectArgs{
-		str: str,
-	}
-	egs.args["Select"] = args
-	return egs
-}
-
-// Cols provides some columns to special
-func (egs *EGSession) Cols(columns ...string) *EGSession {
-	egs.operation = append(egs.operation, "Cols")
-	args := ColsArgs{
-		columns: columns,
-	}
-	egs.args["Cols"] = args
-	return egs
-}
-
-// AllCols ask all columns
-func (egs *EGSession) AllCols() *EGSession {
-	egs.operation = append(egs.operation, "AllCols")
-	return egs
-}
-
-// MustCols specify some columns must use even if they are empty
-func (egs *EGSession) MustCols(columns ...string) *EGSession {
-	egs.operation = append(egs.operation, "MustCols")
-	args := MustColsArgs{
-		columns: columns,
-	}
-	egs.args["MustCols"] = args
-	return egs
-}
-
-// UseBool automatically retrieve condition according struct, but
-// if struct has bool field, it will ignore them. So use UseBool
-// to tell system to do not ignore them.
-// If no parameters, it will use all the bool field of struct, or
-// it will use parameters's columns
-func (egs *EGSession) UseBool(columns ...string) *EGSession {
-	egs.operation = append(egs.operation, "UseBool")
-	args := UseBoolArgs{
-		columns: columns,
-	}
-	egs.args["UseBool"] = args
-	return egs
-}
-
-// Distinct use for distinct columns. Caution: when you are using cache,
-// distinct will not be cached because cache system need id,
-// but distinct will not provide id
-func (egs *EGSession) Distinct(columns ...string) *EGSession {
-	egs.operation = append(egs.operation, "Distinct")
-	args := DistinctArgs{
-		columns: columns,
-	}
-	egs.args["Distinct"] = args
-	return egs
-}
-
-// Omit Only not use the parameters as select or update columns
-func (egs *EGSession) Omit(columns ...string) *EGSession {
-	egs.operation = append(egs.operation, "Omit")
-	args := OmitArgs{
-		columns: columns,
-	}
-	egs.args["Omit"] = args
-	return egs
-}
-
-// Nullable Set null when column is zero-value and nullable for update
-func (egs *EGSession) Nullable(columns ...string) *EGSession {
-	egs.operation = append(egs.operation, "Nullable")
-	args := NullableArgs{
-		columns: columns,
-	}
-	egs.args["Nullable"] = args
-	return egs
-}
-
-// NoAutoTime means do not automatically give created field and updated field
-// the current time on the current session temporarily
-func (egs *EGSession) NoAutoTime() *EGSession {
-	egs.operation = append(egs.operation, "NoAutoTime")
-	return egs
-}
-
-// Sql provides raw sql input parameter. When you have a complex SQL statement
-// and cannot use Where, Id, In and etc. Methods to describe, you can use SQL.
-//
-// Deprecated: use SQL instead.
-func (egs *EGSession) Sql(query string, args ...interface{}) *EGSession {
-	egs.operation = append(egs.operation, "Sql")
-	sqlArgs := SqlArgs{
-		query: query,
-		args:  args,
-	}
-	egs.args["Sql"] = sqlArgs
-	return egs
-}
-
-type SQLArgs struct {
-	query interface{}
-	args  []interface{}
-}
-
-// SQL provides raw sql input parameter. When you have a complex SQL statement
-// and cannot use Where, Id, In and etc. Methods to describe, you can use SQL.
-func (egs *EGSession) SQL(query interface{}, args ...interface{}) *EGSession {
-	egs.operation = append(egs.operation, "SQL")
-	sqlArgs := SQLArgs{
-		query: query,
-		args:  args,
-	}
-	egs.args["SQL"] = sqlArgs
-	return egs
-}
-
-// Where provides custom query condition.
-func (egs *EGSession) Where(query interface{}, args ...interface{}) *EGSession {
-	egs.operation = append(egs.operation, "Where")
-	whereArgs := WhereArgs{
-		query: query,
-		args:  args,
-	}
-	egs.args["Where"] = whereArgs
-	return egs
-}
-
-type AndArgs struct {
-	query interface{}
-	args  []interface{}
-}
-
-// And provides custom query condition.
-func (egs *EGSession) And(query interface{}, args ...interface{}) *EGSession {
-	egs.operation = append(egs.operation, "And")
-	andArgs := AndArgs{
-		query: query,
-		args:  args,
-	}
-	egs.args["And"] = andArgs
-	return egs
-}
-
-type OrArgs struct {
-	query interface{}
-	args  []interface{}
-}
-
-// Or provides custom query condition.
-func (egs *EGSession) Or(query interface{}, args ...interface{}) *EGSession {
-	egs.operation = append(egs.operation, "Or")
-	orArgs := OrArgs{
-		query: query,
-		args:  args,
-	}
-	egs.args["Or"] = orArgs
-	return egs
-}
-
-// Id provides converting id as a query condition
-//
-// Deprecated: use ID instead
-func (egs *EGSession) Id(id interface{}) *EGSession {
-	egs.operation = append(egs.operation, "Id")
-	args := IdArgs{
-		id: id,
-	}
-	egs.args["Id"] = args
-	return egs
-}
-
-// ID provides converting id as a query condition
-func (egs *EGSession) ID(id interface{}) *EGSession {
-	egs.operation = append(egs.operation, "ID")
-	args := IDArgs{
-		id: id,
-	}
-	egs.args["ID"] = args
-	return egs
-}
-
-// In provides a query string like "id in (1, 2, 3)"
-func (egs *EGSession) In(column string, args ...interface{}) *EGSession {
-	egs.operation = append(egs.operation, "In")
-	inArgs := InArgs{
-		column: column,
-		args:   args,
-	}
-	egs.args["In"] = inArgs
-	return egs
-}
-
-// NotIn provides a query string like "id in (1, 2, 3)"
-func (egs *EGSession) NotIn(column string, args ...interface{}) *EGSession {
-	egs.operation = append(egs.operation, "NotIn")
-	notInArgs := NotInArgs{
-		column: column,
-		args:   args,
-	}
-	egs.args["NotIn"] = notInArgs
-	return egs
-}
-
-// Conds returns session query conditions except auto bean conditions
-func (egs *EGSession) Conds() builder.Cond {
-	return egs.eg.Master().NewSession().Conds()
-}
-
-// Delete records, bean's non-empty fields are conditions
-func (egs *EGSession) Delete(bean interface{}) (int64, error) {
-	session := egs.eg.Master().NewSession()
-	defer session.Close()
-	session = egs.operate(session)
-	return session.Delete(bean)
-}
-
-// Exist returns true if the record exist otherwise return false
-func (egs *EGSession) Exist(bean ...interface{}) (bool, error) {
-	session := egs.eg.Master().NewSession()
-	defer session.Close()
-	session = egs.operate(session)
-	return session.Exist(bean...)
-}
-
-// Find retrieve records from table, condiBeans's non-empty fields
-// are conditions. beans could be []Struct, []*Struct, map[int64]Struct
-// map[int64]*Struct
-func (egs *EGSession) Find(rowsSlicePtr interface{}, condiBean ...interface{}) error {
-	session := egs.eg.Slave().NewSession()
-	defer session.Close()
-	session = egs.operate(session)
-	return session.Find(rowsSlicePtr, condiBean...)
-}
-
-// Get retrieve one record from database, bean's non-empty fields
-// will be as conditions
-func (egs *EGSession) Get(bean interface{}) (bool, error) {
-	session := egs.eg.Slave().NewSession()
-	defer session.Close()
-	session = egs.operate(session)
-	return session.Get(bean)
-}
-
-// Insert insert one or more beans
-func (egs *EGSession) Insert(beans ...interface{}) (int64, error) {
-	session := egs.eg.Master().NewSession()
-	defer session.Close()
-	session = egs.operate(session)
-	return session.Insert(beans...)
-}
-
-// Rows return sql.Rows compatible Rows obj, as a forward Iterator object for iterating record by record, bean's non-empty fields
-// are conditions.
-func (egs *EGSession) Rows(bean interface{}) (*Rows, error) {
-	session := egs.eg.Slave().NewSession()
-	defer session.Close()
-	session = egs.operate(session)
-	return session.Rows(bean)
-}
-
-// Iterate record by record handle records from table, condiBeans's non-empty fields
-// are conditions. beans could be []Struct, []*Struct, map[int64]Struct
-// map[int64]*Struct
-func (egs *EGSession) Iterate(bean interface{}, fun IterFunc) error {
-	return egs.eg.Slave().Iterate(bean, fun)
-}
-
-// BufferSize sets the buffersize for iterate
-func (egs *EGSession) BufferSize(size int) *EGSession {
-	egs.operation = append(egs.operation, "BufferSize")
-	args := BufferSizeArgs{
-		size: size,
-	}
-	egs.args["BufferSize"] = args
-	return egs
-}
-
-// Query runs a raw sql and return records as []map[string][]byte
-func (egs *EGSession) Query(sqlStr string, args ...interface{}) ([]map[string][]byte, error) {
-	session := egs.eg.Slave().NewSession()
-	defer session.Close()
-	session = egs.operate(session)
-	return session.Query(sqlStr, args...)
-}
-
-// QueryString runs a raw sql and return records as []map[string]string
-func (egs *EGSession) QueryString(sqlStr string, args ...interface{}) ([]map[string]string, error) {
-	session := egs.eg.Slave().NewSession()
-	defer session.Close()
-	session = egs.operate(session)
-	return session.QueryString(sqlStr, args...)
-}
-
-// QueryInterface runs a raw sql and return records as []map[string]interface{}
-func (egs *EGSession) QueryInterface(sqlStr string, args ...interface{}) ([]map[string]interface{}, error) {
-	session := egs.eg.Slave().NewSession()
-	defer session.Close()
-	session = egs.operate(session)
-	return session.QueryInterface(sqlStr, args...)
-}
-
-// Exec raw sql
-func (egs *EGSession) Exec(sqlStr string, args ...interface{}) (sql.Result, error) {
-	session := egs.eg.Master().NewSession()
-	defer session.Close()
-	session = egs.operate(session)
-	return session.Exec(sqlStr, args...)
-}
-
-// CreateTable create a table according a bean
-func (egs *EGSession) CreateTable(bean interface{}) error {
-	session := egs.eg.Master().NewSession()
-	defer session.Close()
-	return session.CreateTable(bean)
-}
-
-// CreateIndexes create indexes
-func (egs *EGSession) CreateIndexes(bean interface{}) error {
-	return egs.eg.Master().CreateIndexes(bean)
-}
-
-// CreateUniques create uniques
-func (egs *EGSession) CreateUniques(bean interface{}) error {
-	return egs.eg.Master().CreateUniques(bean)
-}
-
-// DropIndexes drop indexes
-func (egs *EGSession) DropIndexes(bean interface{}) error {
-	return egs.eg.Master().DropIndexes(bean)
-}
-
-// DropTable drop table will drop table if exist, if drop failed, it will return error
-func (egs *EGSession) DropTable(beanOrTableName interface{}) error {
-	session := egs.eg.Master().NewSession()
-	defer session.Close()
-	return session.DropTable(beanOrTableName)
-}
-
-// IsTableExist if a table is exist
-func (egs *EGSession) IsTableExist(beanOrTableName interface{}) (bool, error) {
-	return egs.eg.Master().IsTableExist(beanOrTableName)
-}
-
-// IsTableEmpty if table have any records
-func (egs *EGSession) IsTableEmpty(bean interface{}) (bool, error) {
-	return egs.eg.Master().IsTableEmpty(bean)
-}
-
-// Sync2 synchronize structs to database tables
-func (egs *EGSession) Sync2(beans ...interface{}) error {
-	return egs.eg.Master().Sync2(beans...)
-}
-
-// Count counts the records. bean's non-empty fields
-// are conditions.
-func (egs *EGSession) Count(bean ...interface{}) (int64, error) {
-	session := egs.eg.Slave().NewSession()
-	defer session.Close()
-	session = egs.operate(session)
-	return session.Count(bean...)
-}
-
-// sum call sum some column. bean's non-empty fields are conditions.
-func (egs *EGSession) Sum(bean interface{}, columnName string) (res float64, err error) {
-	session := egs.eg.Slave().NewSession()
-	defer session.Close()
-	session = egs.operate(session)
-	return session.Sum(bean, columnName)
-}
-
-// SumInt call sum some column. bean's non-empty fields are conditions.
-func (egs *EGSession) SumInt(bean interface{}, columnName string) (res int64, err error) {
-	session := egs.eg.Slave().NewSession()
-	defer session.Close()
-	session = egs.operate(session)
-	return session.SumInt(bean, columnName)
-}
-
-// Sums call sum some columns. bean's non-empty fields are conditions.
-func (egs *EGSession) Sums(bean interface{}, columnNames ...string) ([]float64, error) {
-	session := egs.eg.Slave().NewSession()
-	defer session.Close()
-	session = egs.operate(session)
-	return session.Sums(bean, columnNames...)
-}
-
-// SumsInt sum specify columns and return as []int64 instead of []float64
-func (egs *EGSession) SumsInt(bean interface{}, columnNames ...string) ([]int64, error) {
-	session := egs.eg.Slave().NewSession()
-	defer session.Close()
-	session = egs.operate(session)
-	return session.SumsInt(bean, columnNames...)
-}
-
-// Update records, bean's non-empty fields are updated contents,
-// condiBean' non-empty filds are conditions
-// CAUTION:
-//        1.bool will defaultly be updated content nor conditions
-//         You should call UseBool if you have bool to use.
-//        2.float32 & float64 may be not inexact as conditions
-func (egs *EGSession) Update(bean interface{}, condiBean ...interface{}) (int64, error) {
-	session := egs.eg.Master().NewSession()
-	defer session.Close()
-	session = egs.operate(session)
-	return session.Update(bean, condiBean...)
-
-}
diff --git a/session.go b/session.go
index c69ac9e5..fe2b9746 100644
--- a/session.go
+++ b/session.go
@@ -258,13 +258,13 @@ func (session *Session) canCache() bool {
 	return true
 }
 
-func (session *Session) doPrepare(sqlStr string) (stmt *core.Stmt, err error) {
+func (session *Session) doPrepare(db *core.DB, sqlStr string) (stmt *core.Stmt, err error) {
 	crc := crc32.ChecksumIEEE([]byte(sqlStr))
 	// TODO try hash(sqlStr+len(sqlStr))
 	var has bool
 	stmt, has = session.stmtCache[crc]
 	if !has {
-		stmt, err = session.DB().Prepare(sqlStr)
+		stmt, err = db.Prepare(sqlStr)
 		if err != nil {
 			return nil, err
 		}
diff --git a/session_raw.go b/session_raw.go
index c225598e..69bf9b3c 100644
--- a/session_raw.go
+++ b/session_raw.go
@@ -47,9 +47,16 @@ func (session *Session) queryRows(sqlStr string, args ...interface{}) (*core.Row
 	}
 
 	if session.isAutoCommit {
+		var db *core.DB
+		if session.engine.engineGroup != nil {
+			db = session.engine.engineGroup.Slave().DB()
+		} else {
+			db = session.DB()
+		}
+
 		if session.prepareStmt {
 			// don't clear stmt since session will cache them
-			stmt, err := session.doPrepare(sqlStr)
+			stmt, err := session.doPrepare(db, sqlStr)
 			if err != nil {
 				return nil, err
 			}
@@ -61,7 +68,7 @@ func (session *Session) queryRows(sqlStr string, args ...interface{}) (*core.Row
 			return rows, nil
 		}
 
-		rows, err := session.DB().Query(sqlStr, args...)
+		rows, err := db.Query(sqlStr, args...)
 		if err != nil {
 			return nil, err
 		}
@@ -171,7 +178,7 @@ func (session *Session) exec(sqlStr string, args ...interface{}) (sql.Result, er
 	}
 
 	if session.prepareStmt {
-		stmt, err := session.doPrepare(sqlStr)
+		stmt, err := session.doPrepare(session.DB(), sqlStr)
 		if err != nil {
 			return nil, err
 		}