diff --git a/callbacks.go b/callbacks.go
index db8261c4..d1164019 100644
--- a/callbacks.go
+++ b/callbacks.go
@@ -90,6 +90,9 @@ func (p *processor) Execute(db *DB) {
 	}
 
 	if stmt := db.Statement; stmt != nil {
+		db.Error = stmt.Error
+		db.RowsAffected = stmt.RowsAffected
+
 		db.Logger.Trace(curTime, func() (string, int64) {
 			return db.Dialector.Explain(stmt.SQL.String(), stmt.Vars...), db.RowsAffected
 		}, db.Error)
diff --git a/callbacks/create.go b/callbacks/create.go
index 2e1b3381..42dcda27 100644
--- a/callbacks/create.go
+++ b/callbacks/create.go
@@ -50,7 +50,7 @@ func Create(db *gorm.DB) {
 	db.Statement.AddClause(ConvertToCreateValues(db.Statement))
 
 	db.Statement.Build("INSERT", "VALUES", "ON_CONFLICT")
-	result, err := db.DB.ExecContext(db.Context, db.Statement.SQL.String(), db.Statement.Vars...)
+	result, err := db.Statement.ConnPool.ExecContext(db.Statement.Context, db.Statement.SQL.String(), db.Statement.Vars...)
 
 	if err == nil {
 		if db.Statement.Schema != nil {
diff --git a/callbacks/delete.go b/callbacks/delete.go
index 05d00d0a..50b2880a 100644
--- a/callbacks/delete.go
+++ b/callbacks/delete.go
@@ -57,7 +57,7 @@ func Delete(db *gorm.DB) {
 		db.Statement.Build("DELETE", "FROM", "WHERE")
 	}
 
-	result, err := db.DB.ExecContext(db.Context, db.Statement.SQL.String(), db.Statement.Vars...)
+	result, err := db.Statement.ConnPool.ExecContext(db.Statement.Context, db.Statement.SQL.String(), db.Statement.Vars...)
 
 	if err == nil {
 		db.RowsAffected, _ = result.RowsAffected()
diff --git a/callbacks/query.go b/callbacks/query.go
index 26c0e0ad..00820bfd 100644
--- a/callbacks/query.go
+++ b/callbacks/query.go
@@ -14,7 +14,7 @@ func Query(db *gorm.DB) {
 		db.Statement.Build("SELECT", "FROM", "WHERE", "GROUP BY", "ORDER BY", "LIMIT", "FOR")
 	}
 
-	rows, err := db.DB.QueryContext(db.Context, db.Statement.SQL.String(), db.Statement.Vars...)
+	rows, err := db.Statement.ConnPool.QueryContext(db.Statement.Context, db.Statement.SQL.String(), db.Statement.Vars...)
 	if err != nil {
 		db.AddError(err)
 		return
diff --git a/callbacks/raw.go b/callbacks/raw.go
index e8cad25d..ce125e61 100644
--- a/callbacks/raw.go
+++ b/callbacks/raw.go
@@ -5,7 +5,7 @@ import (
 )
 
 func RawExec(db *gorm.DB) {
-	result, err := db.DB.ExecContext(db.Context, db.Statement.SQL.String(), db.Statement.Vars...)
+	result, err := db.Statement.ConnPool.ExecContext(db.Statement.Context, db.Statement.SQL.String(), db.Statement.Vars...)
 	if err != nil {
 		db.AddError(err)
 	} else {
diff --git a/callbacks/row.go b/callbacks/row.go
index f7d6752d..b84cf694 100644
--- a/callbacks/row.go
+++ b/callbacks/row.go
@@ -14,8 +14,8 @@ func RowQuery(db *gorm.DB) {
 	}
 
 	if _, ok := db.Get("rows"); ok {
-		db.Statement.Dest, db.Error = db.DB.QueryContext(db.Context, db.Statement.SQL.String(), db.Statement.Vars...)
+		db.Statement.Dest, db.Error = db.Statement.ConnPool.QueryContext(db.Statement.Context, db.Statement.SQL.String(), db.Statement.Vars...)
 	} else {
-		db.Statement.Dest = db.DB.QueryRowContext(db.Context, db.Statement.SQL.String(), db.Statement.Vars...)
+		db.Statement.Dest = db.Statement.ConnPool.QueryRowContext(db.Statement.Context, db.Statement.SQL.String(), db.Statement.Vars...)
 	}
 }
diff --git a/callbacks/update.go b/callbacks/update.go
index ca31bf18..eab9f929 100644
--- a/callbacks/update.go
+++ b/callbacks/update.go
@@ -47,7 +47,7 @@ func Update(db *gorm.DB) {
 	db.Statement.AddClause(ConvertToAssignments(db.Statement))
 	db.Statement.Build("UPDATE", "SET", "WHERE")
 
-	result, err := db.DB.ExecContext(db.Context, db.Statement.SQL.String(), db.Statement.Vars...)
+	result, err := db.Statement.ConnPool.ExecContext(db.Statement.Context, db.Statement.SQL.String(), db.Statement.Vars...)
 
 	if err == nil {
 		db.RowsAffected, _ = result.RowsAffected()
diff --git a/chainable_api.go b/chainable_api.go
index 6f80d4be..98c1898e 100644
--- a/chainable_api.go
+++ b/chainable_api.go
@@ -5,6 +5,7 @@ import (
 	"strings"
 
 	"github.com/jinzhu/gorm/clause"
+	"github.com/jinzhu/gorm/utils"
 )
 
 // Model specify the model you would like to run db operations
@@ -64,7 +65,7 @@ func (db *DB) Select(query interface{}, args ...interface{}) (tx *DB) {
 			}
 		}
 	case string:
-		fields := strings.FieldsFunc(v, isChar)
+		fields := strings.FieldsFunc(v, utils.IsChar)
 
 		// normal field names
 		if len(fields) == 1 || (len(fields) == 3 && strings.ToUpper(fields[1]) == "AS") {
@@ -100,7 +101,7 @@ func (db *DB) Omit(columns ...string) (tx *DB) {
 	tx = db.getInstance()
 
 	if len(columns) == 1 && strings.ContainsRune(columns[0], ',') {
-		tx.Statement.Omits = strings.FieldsFunc(columns[0], isChar)
+		tx.Statement.Omits = strings.FieldsFunc(columns[0], utils.IsChar)
 	} else {
 		tx.Statement.Omits = columns
 	}
diff --git a/dialects/mssql/mssql.go b/dialects/mssql/mssql.go
index 91574787..7e51de75 100644
--- a/dialects/mssql/mssql.go
+++ b/dialects/mssql/mssql.go
@@ -26,8 +26,7 @@ func Open(dsn string) gorm.Dialector {
 func (dialector Dialector) Initialize(db *gorm.DB) (err error) {
 	// register callbacks
 	callbacks.RegisterDefaultCallbacks(db)
-
-	db.DB, err = sql.Open("sqlserver", dialector.DSN)
+	db.ConnPool, err = sql.Open("sqlserver", dialector.DSN)
 	return
 }
 
diff --git a/dialects/mysql/mysql.go b/dialects/mysql/mysql.go
index 9d16507e..55b5a53f 100644
--- a/dialects/mysql/mysql.go
+++ b/dialects/mysql/mysql.go
@@ -25,7 +25,7 @@ func Open(dsn string) gorm.Dialector {
 func (dialector Dialector) Initialize(db *gorm.DB) (err error) {
 	// register callbacks
 	callbacks.RegisterDefaultCallbacks(db)
-	db.DB, err = sql.Open("mysql", dialector.DSN)
+	db.ConnPool, err = sql.Open("mysql", dialector.DSN)
 	return
 }
 
diff --git a/dialects/postgres/postgres.go b/dialects/postgres/postgres.go
index 0005f7ed..e90fa4ae 100644
--- a/dialects/postgres/postgres.go
+++ b/dialects/postgres/postgres.go
@@ -26,8 +26,7 @@ func Open(dsn string) gorm.Dialector {
 func (dialector Dialector) Initialize(db *gorm.DB) (err error) {
 	// register callbacks
 	callbacks.RegisterDefaultCallbacks(db)
-
-	db.DB, err = sql.Open("postgres", dialector.DSN)
+	db.ConnPool, err = sql.Open("postgres", dialector.DSN)
 	return
 }
 
diff --git a/dialects/sqlite/sqlite.go b/dialects/sqlite/sqlite.go
index 91762343..8e3cc058 100644
--- a/dialects/sqlite/sqlite.go
+++ b/dialects/sqlite/sqlite.go
@@ -23,7 +23,7 @@ func Open(dsn string) gorm.Dialector {
 func (dialector Dialector) Initialize(db *gorm.DB) (err error) {
 	// register callbacks
 	callbacks.RegisterDefaultCallbacks(db)
-	db.DB, err = sql.Open("sqlite3", dialector.DSN)
+	db.ConnPool, err = sql.Open("sqlite3", dialector.DSN)
 	return
 }
 
diff --git a/helpers.go b/errors.go
similarity index 60%
rename from helpers.go
rename to errors.go
index 241d3fbd..32f55e01 100644
--- a/helpers.go
+++ b/errors.go
@@ -2,8 +2,6 @@ package gorm
 
 import (
 	"errors"
-	"time"
-	"unicode"
 )
 
 var (
@@ -20,19 +18,3 @@ var (
 	// ErrMissingWhereClause missing where clause
 	ErrMissingWhereClause = errors.New("missing WHERE clause while deleting")
 )
-
-// Model a basic GoLang struct which includes the following fields: ID, CreatedAt, UpdatedAt, DeletedAt
-// It may be embeded into your model or you may build your own model without it
-//    type User struct {
-//      gorm.Model
-//    }
-type Model struct {
-	ID        uint `gorm:"primarykey"`
-	CreatedAt time.Time
-	UpdatedAt time.Time
-	DeletedAt *time.Time `gorm:"index"`
-}
-
-func isChar(c rune) bool {
-	return !unicode.IsLetter(c) && !unicode.IsNumber(c)
-}
diff --git a/finisher_api.go b/finisher_api.go
index 51d9b409..62c1af30 100644
--- a/finisher_api.go
+++ b/finisher_api.go
@@ -196,14 +196,14 @@ func (db *DB) Transaction(fc func(tx *DB) error, opts ...*sql.TxOptions) (err er
 // Begin begins a transaction
 func (db *DB) Begin(opts ...*sql.TxOptions) (tx *DB) {
 	tx = db.getInstance()
-	if beginner, ok := tx.DB.(TxBeginner); ok {
+	if beginner, ok := tx.Statement.ConnPool.(TxBeginner); ok {
 		var opt *sql.TxOptions
 		var err error
 		if len(opts) > 0 {
 			opt = opts[0]
 		}
 
-		if tx.DB, err = beginner.BeginTx(db.Context, opt); err != nil {
+		if tx.Statement.ConnPool, err = beginner.BeginTx(db.Statement.Context, opt); err != nil {
 			tx.AddError(err)
 		}
 	} else {
@@ -214,7 +214,7 @@ func (db *DB) Begin(opts ...*sql.TxOptions) (tx *DB) {
 
 // Commit commit a transaction
 func (db *DB) Commit() *DB {
-	if comminter, ok := db.DB.(TxCommiter); ok && comminter != nil {
+	if comminter, ok := db.Statement.ConnPool.(TxCommiter); ok && comminter != nil {
 		db.AddError(comminter.Commit())
 	} else {
 		db.AddError(ErrInvalidTransaction)
@@ -224,7 +224,7 @@ func (db *DB) Commit() *DB {
 
 // Rollback rollback a transaction
 func (db *DB) Rollback() *DB {
-	if comminter, ok := db.DB.(TxCommiter); ok && comminter != nil {
+	if comminter, ok := db.Statement.ConnPool.(TxCommiter); ok && comminter != nil {
 		db.AddError(comminter.Rollback())
 	} else {
 		db.AddError(ErrInvalidTransaction)
diff --git a/gorm.go b/gorm.go
index eac95868..b238d572 100644
--- a/gorm.go
+++ b/gorm.go
@@ -21,23 +21,25 @@ type Config struct {
 	Logger logger.Interface
 	// NowFunc the function to be used when creating a new timestamp
 	NowFunc func() time.Time
-}
 
-type shared struct {
+	// ClauseBuilders clause builder
+	ClauseBuilders map[string]clause.ClauseBuilder
+	// ConnPool db conn pool
+	ConnPool ConnPool
+	// Dialector database dialector
+	Dialector
+
 	callbacks  *callbacks
 	cacheStore *sync.Map
-	quoteChars [2]byte
 }
 
 // DB GORM DB definition
 type DB struct {
 	*Config
-	Dialector
-	Instance
-	ClauseBuilders map[string]clause.ClauseBuilder
-	DB             CommonDB
-	clone          bool
-	*shared
+	Error        error
+	RowsAffected int64
+	Statement    *Statement
+	clone        bool
 }
 
 // Session session config when create session with Session() method
@@ -65,14 +67,17 @@ func Open(dialector Dialector, config *Config) (db *DB, err error) {
 		config.NowFunc = func() time.Time { return time.Now().Local() }
 	}
 
+	if dialector != nil {
+		config.Dialector = dialector
+	}
+
+	if config.cacheStore == nil {
+		config.cacheStore = &sync.Map{}
+	}
+
 	db = &DB{
-		Config:         config,
-		Dialector:      dialector,
-		ClauseBuilders: map[string]clause.ClauseBuilder{},
-		clone:          true,
-		shared: &shared{
-			cacheStore: &sync.Map{},
-		},
+		Config: config,
+		clone:  true,
 	}
 
 	db.callbacks = initializeCallbacks(db)
@@ -91,7 +96,7 @@ func (db *DB) Session(config *Session) *DB {
 	)
 
 	if config.Context != nil {
-		tx.Context = config.Context
+		tx.Statement.Context = config.Context
 	}
 
 	if config.Logger != nil {
@@ -142,23 +147,26 @@ func (db *DB) AutoMigrate(dst ...interface{}) error {
 	return db.Migrator().AutoMigrate(dst...)
 }
 
+// AddError add error to db
+func (db *DB) AddError(err error) {
+	db.Statement.AddError(err)
+}
+
 func (db *DB) getInstance() *DB {
 	if db.clone {
-		ctx := db.Instance.Context
-		if ctx == nil {
-			ctx = context.Background()
+		ctx := context.Background()
+		if db.Statement != nil {
+			ctx = db.Statement.Context
 		}
 
 		return &DB{
-			Instance: Instance{
-				Context:   ctx,
-				Statement: &Statement{DB: db, Clauses: map[string]clause.Clause{}},
+			Config: db.Config,
+			Statement: &Statement{
+				DB:       db,
+				ConnPool: db.ConnPool,
+				Clauses:  map[string]clause.Clause{},
+				Context:  ctx,
 			},
-			Config:         db.Config,
-			Dialector:      db.Dialector,
-			ClauseBuilders: db.ClauseBuilders,
-			DB:             db.DB,
-			shared:         db.shared,
 		}
 	}
 
diff --git a/interfaces.go b/interfaces.go
index c89c3624..9859d1fa 100644
--- a/interfaces.go
+++ b/interfaces.go
@@ -18,8 +18,8 @@ type Dialector interface {
 	Explain(sql string, vars ...interface{}) string
 }
 
-// CommonDB common db interface
-type CommonDB interface {
+// ConnPool db conns pool interface
+type ConnPool interface {
 	ExecContext(ctx context.Context, query string, args ...interface{}) (sql.Result, error)
 	PrepareContext(ctx context.Context, query string) (*sql.Stmt, error)
 	QueryContext(ctx context.Context, query string, args ...interface{}) (*sql.Rows, error)
diff --git a/model.go b/model.go
new file mode 100644
index 00000000..fdee99dc
--- /dev/null
+++ b/model.go
@@ -0,0 +1,15 @@
+package gorm
+
+import "time"
+
+// Model a basic GoLang struct which includes the following fields: ID, CreatedAt, UpdatedAt, DeletedAt
+// It may be embeded into your model or you may build your own model without it
+//    type User struct {
+//      gorm.Model
+//    }
+type Model struct {
+	ID        uint `gorm:"primarykey"`
+	CreatedAt time.Time
+	UpdatedAt time.Time
+	DeletedAt *time.Time `gorm:"index"`
+}
diff --git a/statement.go b/statement.go
index f04ea269..10b62567 100644
--- a/statement.go
+++ b/statement.go
@@ -14,30 +14,6 @@ import (
 	"github.com/jinzhu/gorm/schema"
 )
 
-// Instance db instance
-type Instance struct {
-	Error        error
-	RowsAffected int64
-	Context      context.Context
-	Statement    *Statement
-}
-
-func (instance *Instance) ToSQL(clauses ...string) (string, []interface{}) {
-	if len(clauses) > 0 {
-		instance.Statement.Build(clauses...)
-	}
-	return strings.TrimSpace(instance.Statement.SQL.String()), instance.Statement.Vars
-}
-
-// AddError add error to instance
-func (inst *Instance) AddError(err error) {
-	if inst.Error == nil {
-		inst.Error = err
-	} else if err != nil {
-		inst.Error = fmt.Errorf("%v; %w", inst.Error, err)
-	}
-}
-
 // Statement statement
 type Statement struct {
 	Table                string
@@ -48,8 +24,12 @@ type Statement struct {
 	Selects              []string // selected columns
 	Omits                []string // omit columns
 	Settings             sync.Map
+	ConnPool             ConnPool
 	DB                   *DB
 	Schema               *schema.Schema
+	Context              context.Context
+	Error                error
+	RowsAffected         int64
 	RaiseErrorOnNotFound bool
 
 	// SQL Builder
@@ -246,6 +226,14 @@ func (stmt Statement) BuildCondtion(query interface{}, args ...interface{}) (con
 	return conditions
 }
 
+func (stmt *Statement) AddError(err error) {
+	if stmt.Error == nil {
+		stmt.Error = err
+	} else if err != nil {
+		stmt.Error = fmt.Errorf("%v; %w", stmt.Error, err)
+	}
+}
+
 // Build build sql with clauses names
 func (stmt *Statement) Build(clauses ...string) {
 	var firstClauseWritten bool
diff --git a/utils/utils.go b/utils/utils.go
index e7ed512c..25cd585a 100644
--- a/utils/utils.go
+++ b/utils/utils.go
@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"regexp"
 	"runtime"
+	"unicode"
 )
 
 var goSrcRegexp = regexp.MustCompile(`/gorm/.*.go`)
@@ -18,3 +19,7 @@ func FileWithLineNum() string {
 	}
 	return ""
 }
+
+func IsChar(c rune) bool {
+	return !unicode.IsLetter(c) && !unicode.IsNumber(c)
+}