join_ids_better.go

package main

import (
	"fmt"
	"log"
	"reflect"
	"strings"
)

type model struct {
	ID int
}

func joinIds(slice interface{}, idFunc func(i int) string, joiner string) string {
	rv := reflect.ValueOf(slice)
	ids := make([]string, rv.Len())
	for i := 0; i < rv.Len(); i++ {
		ids[i] = idFunc(i)
	}
	return strings.Join(ids, joiner)
}

func run() {
	models := []model{}
	query := "SELECT id FROM blah WHERE id in (%s)"
	f := func(i int) string { return fmt.Sprint(models[i].ID) }
	rows, err := db.Query(fmt.Sprint(query, joinIds(models, f, ",")))
  ...
  ...
}