type Session struct {
	db *sql.DB
	tx *sql.Tx

	// table
	tableMeta *table.TableMeta

	dial dialect.Dialect
	// clause

	clause clause.Clause

	// sql query
	sql strings.Builder
	// sql param
	sqlParam []interface{}
}

// Parse 將結(jié)構(gòu)體轉(zhuǎn)化成 表/字段/字段類型
func Parse(dest interface{}, d dialect.Dialect) *TableMeta {
	// 是否為nil
	if dest == nil {
		returnnil
	}
	// (*User)(nil)
	value := reflect.ValueOf(dest)
	if value.Kind() == reflect.Ptr && value.IsNil() {
		value = reflect.New(value.Type().Elem()) // 取出類型，構(gòu)造新對(duì)象
	}
	meta := &TableMeta{
		Model:    value.Interface(), // 保存對(duì)象
		fieldMap: make(map[string]*Field),
	}
	destValue := reflect.Indirect(value)
	destType := destValue.Type()
	// 結(jié)構(gòu)體類型名：就是表名
	m, ok := value.Interface().(Tabler)
	if ok {
		meta.TableName = m.TableName()
	} else {
		meta.TableName = destType.Name()
	}
	for i := 0; i < destType.NumField(); i++ {
		fieldType := destType.Field(i)
		// 非匿名 && 可導(dǎo)出
		if !fieldType.Anonymous && fieldType.IsExported() {
			// 成員變量：就是字段名
			// 成員變量類型：就是字段類型
			field := &Field{
				FieldName: fieldType.Name,
				FieldType: d.ConvertType2DBType(destValue.Field(i)),
				FieldTag:  fieldType.Tag.Get("easyorm"),
			}
			meta.Fields = append(meta.Fields, field)
			meta.FieldsName = append(meta.FieldsName, field.FieldName)
			meta.fieldMap[field.FieldName] = field
		}
	}
	return meta
}

// s.Insert(&User{},&User{})
func (s *Session) Insert(values ...interface{}) (int64, error) {
	iflen(values) == 0 {
		return0, errors.New("param is empty")
	}
	// init table
	s.Model(values[0])
	// clause insert：負(fù)責(zé)生成 insert into $tableName ($FieldName) 字符串
	s.clause.Set(clause.INSERT, s.TableMeta().TableName, s.TableMeta().FieldsName)

	valueSlice := []interface{}{}

	for _, value := range values {
		s.CallMethod(BeforeInsert, value)
        // 提取結(jié)構(gòu)體中對(duì)象字段的值，作為sql語(yǔ)言的參數(shù)
		valueSlice = append(valueSlice, s.TableMeta().ExtractFieldValue(value))
	}
	// clause values：負(fù)責(zé)生成 values (?,?,?),(?,?,?)
	s.clause.Set(clause.VALUES, valueSlice...)
    //s.clause.Build: 負(fù)責(zé)將 insert into $tableName ($FieldName)  拼接上 values (?,?,?),(?,?,?) 形成完整的sql語(yǔ)句
	sql, sqlParam := s.clause.Build(clause.INSERT, clause.VALUES)
	// exec sql ： 實(shí)際執(zhí)行sql
	result, err := s.Raw(sql, sqlParam...).Exec()
	if err != nil {
		return0, err
	}
	s.CallMethod(AfterInsert, nil)
	return result.RowsAffected()
}

// TxFunc will be called between tx.Begin() and tx.Commit()
type TxFunc func(*session.Session) (interface{}, error)
// Transaction executes sql wrapped in a transaction, then automatically commit if no error occurs
func (engine *Engine) Transaction(f TxFunc) (result interface{}, err error) {
	s := engine.NewSession()
	if err := s.Begin(); err != nil {
		returnnil, err
	}
	deferfunc() {
		if p := recover(); p != nil {
			_ = s.Rollback()
			panic(p) // re-throw panic after Rollback
		} elseif err != nil {
			_ = s.Rollback() // err is non-nil; don't change it
		} else {
			err = s.Commit() // err is nil; if Commit returns error update err
		}
	}()
	return f(s)
}

// CallMethod calls the registered hooks
func (s *Session) CallMethod(method string, value interface{}) {
	fm := reflect.ValueOf(s.TableMeta().Model).MethodByName(method)
	if value != nil {
		fm = reflect.ValueOf(value).MethodByName(method)
	}
	param := []reflect.Value{reflect.ValueOf(s)}
	if fm.IsValid() {
		if v := fm.Call(param); len(v) > 0 {
			if err, ok := v[0].Interface().(error); ok {
				logger.Error(err)
			}
		}
	}
}