gorm/dialect.go

package gorm

import (
	"database/sql"
	"fmt"
	"reflect"
	"strconv"
	"strings"
)

// Dialect interface contains behaviors that differ across SQL database
type Dialect interface {
	// BindVar return the placeholder for actual values in SQL statements, in many dbs it is "?", Postgres using $1
	BindVar(i int) string
	// Quote quotes field name to avoid SQL parsing exceptions by using a reserved word as a field name
	Quote(key string) string
	// DataTypeOf return data's sql type
	DataTypeOf(field *StructField) string

	// HasIndex check has index or not
	HasIndex(scope *Scope, tableName string, indexName string) bool
	// RemoveIndex remove index
	RemoveIndex(scope *Scope, indexName string)
	// HasTable check has table or not
	HasTable(scope *Scope, tableName string) bool
	// HasColumn check has column or not
	HasColumn(scope *Scope, tableName string, columnName string) bool

	// LimitAndOffsetSQL return generate SQL with limit and offset, as mssql has special case
	LimitAndOffsetSQL(limit, offset int) string
	// SelectFromDummyTable return select values, for most dbs, `SELECT values` just works, mysql needs `SELECT value FROM DUAL`
	SelectFromDummyTable() string
	// LastInsertIdReturningSuffix most dbs support LastInsertId, but postgres needs to use `RETURNING`
	LastInsertIdReturningSuffix(tableName, columnName string) string
}

var dialectsMap = map[string]Dialect{}

func newDialect(name string) Dialect {
	if dialect, ok := dialectsMap[name]; ok {
		return dialect
	}
	fmt.Printf("`%v` is not officially supported, running under compatibility mode.\n", name)
	return &commonDialect{}
}

// RegisterDialect register new dialect
func RegisterDialect(name string, dialect Dialect) {
	dialectsMap[name] = dialect
}

// ParseFieldStructForDialect parse field struct for dialect
func ParseFieldStructForDialect(field *StructField) (fieldValue reflect.Value, sqlType string, size int, additionalType string) {
	// Get redirected field type
	var reflectType = field.Struct.Type
	for reflectType.Kind() == reflect.Ptr {
		reflectType = reflectType.Elem()
	}

	// Get redirected field value
	fieldValue = reflect.Indirect(reflect.New(reflectType))

	// Get scanner's real value
	var getScannerValue func(reflect.Value)
	getScannerValue = func(value reflect.Value) {
		fieldValue = value
		if _, isScanner := reflect.New(fieldValue.Type()).Interface().(sql.Scanner); isScanner && fieldValue.Kind() == reflect.Struct {
			getScannerValue(fieldValue.Field(0))
		}
	}
	getScannerValue(fieldValue)

	// Default Size
	if num, ok := field.TagSettings["SIZE"]; ok {
		size, _ = strconv.Atoi(num)
	} else {
		size = 255
	}

	// Default type from tag setting
	additionalType = field.TagSettings["NOT NULL"] + " " + field.TagSettings["UNIQUE"]
	if value, ok := field.TagSettings["DEFAULT"]; ok {
		additionalType = additionalType + " DEFAULT " + value
	}

	return fieldValue, field.TagSettings["TYPE"], size, strings.TrimSpace(additionalType)
}