Repository for dynamic insertion

repository.go

package repository

import (
	"fmt"
	"strings"
)

type Row interface {
	SetPos(pos int)
	Values() []any
	Insert() string
}

type Rows interface {
	Insert() string
	Values() []any
}

type offer struct {
	pos         int
	ID          int64
	DownPayment string
	Term        string
}

func (o *offer) SetPos(pos int) {
	o.pos = pos
}

func (o *offer) Insert() string {
	return fmt.Sprintf(`(
		(select id from loans where guid = $%d),
		$%d,
		$%d
	)`,
		o.pos+1,
		o.pos+2,
		o.pos+3,
	)
}

func (o *offer) Values() []any {
	return []any{
		o.ID,
		o.DownPayment,
		o.Term,
	}
}

type offers []offer

func (o offers) Insert() string {
	pos := 0
	values := make([]string, len(o))
	for i, item := range o {
		item.SetPos(pos)
		values[i] = item.Insert()
		pos += len(item.Values())
	}
	return fmt.Sprintf("insert into loan_offers values %s", strings.Join(values, ","))
}

func (o offers) Values() []any {
	values := make([]any, 0)

	for _, item := range o {
		values = append(values, item.Values()...)
	}
	return values
}

func (r *repository) DoSomething(offers Rows) error {
	return r.db.Exec(offers.Insert(), offers.Values()...)
}