simple migrator for go

migrator.go

package main

import (
	"bufio"
	"database/sql"
	"fmt"
	"io/ioutil"
	"log"
	"os"
	"path/filepath"
	"sort"
)

var createTrackerSQL = `create table if not exists schema_migrator(name varchar(255) primary key)`
var addTrackerSQL = `insert into schema_migrator values($1)`

// Migrate performs db migration by loaing files from db/*.sql
// and applying any previously unran ones in alphabetical order
func Migrate(db *sql.DB) error {
	db.Exec(createTrackerSQL)
	return loadFiles(db)
}

func loadFiles(db *sql.DB) error {
	rows, err := db.Query("select * from schema_migrator order by name")
	if err != nil {
		return err
	}
	defer rows.Close()
	has := map[string]bool{}
	for rows.Next() {
		var s string
		err = rows.Scan(&s)
		if err != nil {
			return err
		}
		has[s] = true
	}
	files, err := filepath.Glob("db/*.sql")
	if err != nil {
		return err
	}
	sort.Strings(files)

	for _, file := range files {
		b := filepath.Base(file)
		if has[b] {
			// log.Println("Skipping:", b)
		} else {
			err = loadFile(file, db)
			if err != nil {
				return fmt.Errorf("Error applying: %s, reason: %v", b, err)
			}
		}
	}
	return nil
}

func loadFile(file string, db *sql.DB) error {
	f, err := os.Open(file)
	if err != nil {
		return fmt.Errorf("Error reading: %s, reason: %v", file, err)
	}
	defer f.Close()

	r := bufio.NewReader(f)
	buff, err := ioutil.ReadAll(r)
	if err != nil {
		return err
	}
	tx, err := db.Begin()
	if err != nil {
		return err
	}
	defer tx.Rollback()
	_, err = tx.Exec(string(buff))
	if err != nil {
		return fmt.Errorf("SQL:\n%s\nFile: %s\nERROR: %v", string(buff), file, err)
	}
	_, err = tx.Exec(addTrackerSQL, filepath.Base(file))
	if err != nil {
		return fmt.Errorf("Error recording schema migration tracker: %v", err)
	}
	log.Println("Applied migration:", file)
	tx.Commit()
	return nil
}