struct.go

package querybuilder

import (
	"errors"
	"reflect"
	"sort"
	"strings"
)

type KeyValue struct {
	Key   string
	Value interface{}
}

type IndexedColumnValues map[int]KeyValue

func mapToIndexColumnValue(columnValues map[string]interface{}) IndexedColumnValues {
	indexedColumnValues := make(IndexedColumnValues, len(columnValues))
	columns := make([]string, len(columnValues))
	i := 0
	for column := range columnValues {
		columns[i] = column
		i++
	}
	sort.Strings(columns)

	for i = 0; i < len(columns); i++ {
		indexedColumnValues[i] = KeyValue{
			Key:   columns[i],
			Value: columnValues[columns[i]],
		}
	}

	return indexedColumnValues
}

func structToMap(s interface{}) (IndexedColumnValues, error) {
	columnValues := make(IndexedColumnValues)
	v := reflect.ValueOf(s)
	// if its a pointer, resolve its value
	if v.Kind() == reflect.Ptr {
		v = reflect.Indirect(v)
	}

	if v.Kind() != reflect.Struct {
		return nil, errors.New("unexpected type")
	}
	e := v.Type()
	columnIndex := 0
	for i := 0; i < e.NumField(); i++ {
		name := e.Field(i).Name
		tag := strings.Split(e.Field(i).Tag.Get("db"), ",")[0] // use split to ignore tag "options"

		// ignore columns with -
		if tag == "-" {
			continue
		}
		value := v.FieldByIndex(e.Field(i).Index)
		column := tag
		if tag == "" {
			column = name
		}
		if e.Field(i).Type.Kind() == reflect.Struct {
			st := reflect.TypeOf(value.Interface())
			if _, ok := st.MethodByName("String"); !ok {
				nestedColumnValues, err := structToMap(value.Interface())
				if err != nil {
					return nil, err
				}
				for index := 0; index < len(nestedColumnValues); index++ {
					columnValues[columnIndex] = KeyValue{Key: nestedColumnValues[index].Key, Value: nestedColumnValues[index].Value}
					columnIndex++
				}
				continue
			}
		}

		// ignore nil pointer values
		if value.IsZero() && value.Kind() == reflect.Ptr {
			continue
		}
		// if the value is a pointer, resolve its value
		if value.Kind() == reflect.Ptr {
			value = reflect.Indirect(value)
		}
		// if the value is nil, skip adding it
		if value.Interface() == nil {
			continue
		}

		columnValues[columnIndex] = KeyValue{Key: column, Value: value.Interface()}
		columnIndex++
	}
	return columnValues, nil
}