Proof of Concept: scan to pointer in go

nilscan.go

package sqlx

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

var (
	mapper = NewMapperFunc("db", func (u string) string {
		buf := bytes.NewBufferString("")
		for i, v := range u {
			if i > 0 && v >= 'A' && v <= 'Z' {
				buf.WriteRune('_')
			}
			buf.WriteRune(v)
		}
		
		s := strings.ToLower(buf.String())
		return s
	})
)

// Scan a sql.Rows mapping NULL values to nil pointer into the destination
func NilScan(row *sql.Rows, dest interface{}) error {
	destType := reflect.TypeOf(dest)
	destValue := reflect.ValueOf(dest)
	fieldMap := mapper.TypeMap(destType)
	
	columns, _ := row.Columns()
	values := make([]interface{}, len(columns))
	for i := range values {
		values[i] = &sql.NullString{}
	}
	
	err := row.Scan(values...)
	if err != nil {
		return err
	}
	
	for index, name := range columns {
		if indexes, found := fieldMap[name]; found {
			field := FieldByIndexes(destValue, indexes)
			value := values[index].(*sql.NullString)
			
			if value.Valid == false {
				field.Set(reflect.Zero(field.Type()))
				continue
			}
			
			switch field.Interface().(type) {
				case *int64:
					v, err := strconv.ParseInt(value.String, 10, 64)
					if err != nil {
						return fmt.Errorf("unable to parse \"%v\" as int", value.String)
					}
					
					field.Set(reflect.ValueOf(&v))
					continue
					
				case int64:
					v, err := strconv.ParseInt(value.String, 10, 64)
					if err != nil {
						return fmt.Errorf("unable to parse \"%v\" as int", value.String)
					}
					
					field.SetInt(v)
					continue
					
				case *float64:
					v, err := strconv.ParseFloat(value.String, 'f')
					if err != nil {
						return fmt.Errorf("unable to parse \"%v\" as float", value.String)
					}
					
					field.Set(reflect.ValueOf(&v))
					continue
					
				case float64:
					v, err := strconv.ParseFloat(value.String, 'f')
					if err != nil {
						return fmt.Errorf("unable to parse \"%v\" as float", value.String)
					}
					
					field.SetFloat(v)
					continue
				
				case *string:
					field.Set(reflect.ValueOf(&value.String))
					continue
				
				case string:
					field.SetString(value.String)
					continue
			}
		}
	}
	
	return nil
}