csvgen

I’m working quite a bit with CSV files, from imports I’m writing at work to imports I need for my personal ledger setup where I convert those exports I get from my bank about my accounts and convert them to ledger entries.

So, I need to create new parsers quite often and dealing with the same setup and parsing logic has now annoyed me enough that I’ve created a little code-generator for Go that does that for me. The idea is, that I just put a simple configuration file (i.e. csvgen.yml) into a Go package, add a go:generate line and I’d get all the scaffolding. The output of all that is gitlab.com/zerok/csvgen 🥳

So, let’s assume that I have a CSV file that looks like this:

15.12.2003,Name 1
18.03.2004,Name 2

The first column is a date formatted as is common in German-speaking countries while the other column is just some plain text. The configuration file for this would look like that:

---
processors:
- type: RecordProcessor
  recordType: Record
  comma: ","
  fields:
    Date:
      column: 0
      decoder:
        name: parseDate
    Description:
      column: 1

And finally, the code I’d have to write myself is just this one:

package main

import (
	"context"
	"encoding/csv"
	"fmt"
	"os"
	"time"
)

type Record struct {
	Date        time.Time
	Description string
}

func parseDate(ctx context.Context, value string) (time.Time, error) {
	return time.Parse("02.01.2006", value)
}

//go:generate csvgen --output gen_recordprocessor.go
type RecordProcessor struct {
	reader *csv.Reader
}

func main() {
	fp, _ := os.Open("test.csv")
	defer fp.Close()
	processor := NewRecordProcessor(fp)
	records, err := processor.ReadAll(context.Background())
	if err != nil {
        panic(err.Error())
	}
	fmt.Println(records)
}

When I now run go generate . within this package, it will generate a constructor for the RecordProcessor called NewRecordProcessor which accepts an io.Reader and also produce reader methods which convert the records from the CSV file into properly typed values for the Record struct.

Right now, that’s all that csvgen does. As a next step, I want it to also offer some value parsers that I’ve need again and again. In the future there might also be some CSV-writing functionality alongside the reader which was the main reason why I called the main type “Processor” and not just “Reader” or “Parser”. Let’s see 🙂