field_column.go

package do

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

// FieldsByColumnType t is a struct pointer, and use it's field match column name to receive scan value. It will use db tag to get column name first, or lower case field name. You can specify fieldMapper to control column name with field name
func FieldsByColumnType(t any, colTypes []*sql.ColumnType, fieldMapper func(string) string) (fields []any) {
	validName := make(map[string]struct{})
	for _, ct := range colTypes {
		validName[ct.Name()] = struct{}{}
	}

	nameValues := fieldsByColumnName(t, validName, fieldMapper)

	for _, ct := range colTypes {
		fields = append(fields, nameValues[ct.Name()])
	}

	return
}

func fieldsByColumnName(t any, validName map[string]struct{}, fieldMapper func(string) string) (nameValues map[string]any) {
	val := reflect.ValueOf(t)
	typ := val.Type()
	if typ.Kind() != reflect.Ptr {
		panic(fmt.Errorf("t must be a struct pointer"))
	}
	val = val.Elem()
	typ = typ.Elem()
	if typ.Kind() != reflect.Struct {
		panic(fmt.Errorf("t must be a struct pointer"))
	}

	return fieldsByColumnNameInner(typ, val, validName, fieldMapper)
}

func fieldsByColumnNameInner(typ reflect.Type, val reflect.Value, validName map[string]struct{}, fieldMapper func(string) string) (nameValues map[string]any) {
	nameValues = make(map[string]any)
	for i := 0; i < typ.NumField(); i++ {
		field := typ.Field(i)
		value := val.Field(i)

		if field.Anonymous {
			nv := fieldsByColumnNameInner(value.Type(), value, validName, fieldMapper)
			nameValues = MergeKeyValue(nameValues, nv)
		} else {
			fieldName := ""
			if fieldMapper == nil {
				fieldName = field.Tag.Get("db")
				if fieldName == "" {
					fieldName = strings.ToLower(field.Name)
				}
			} else {
				fieldName = fieldMapper(field.Name)
			}

			if _, ok := validName[fieldName]; !ok {
				continue
			}

			nameValues[fieldName] = value.Addr().Interface()
		}
	}

	return
}