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postgres.go
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postgres.go
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package postgres
import (
"database/sql"
"fmt"
"hash/crc32"
"io"
"io/ioutil"
nurl "net/url"
"github.com/lib/pq"
"github.com/mattes/migrate/database"
)
func init() {
database.Register("postgres", &Postgres{})
}
type Config struct {
}
func WithInstance(instance *sql.DB, config *Config) (database.Driver, error) {
return &Postgres{
db: instance,
config: config,
}, nil
}
type Postgres struct {
db *sql.DB
url *nurl.URL
isLocked bool
config *Config
}
var (
ErrNoSqlInstance = fmt.Errorf("expected *sql.DB")
ErrNoDatabaseName = fmt.Errorf("no database name")
)
const tableName = "schema_migrations"
func (p *Postgres) Open(url string) (database.Driver, error) {
purl, err := nurl.Parse(url)
if err != nil {
return nil, err
}
db, err := sql.Open("postgres", url)
if err != nil {
return nil, err
}
if err := db.Ping(); err != nil {
return nil, err
}
px := &Postgres{
db: db,
url: purl,
}
if err := px.ensureVersionTable(); err != nil {
return nil, err
}
return px, nil
}
func (p *Postgres) Close() error {
return p.db.Close()
}
// https://www.postgresql.org/docs/9.6/static/explicit-locking.html#ADVISORY-LOCKS
func (p *Postgres) Lock() error {
if p.isLocked {
return database.ErrLocked
}
aid, err := p.generateAdvisoryLockId()
if err != nil {
return err
}
// It will either obtain the lock immediately and return true, or return false if the lock cannot be acquired immediately.
var success bool
if err := p.db.QueryRow("SELECT pg_try_advisory_lock($1)", aid).Scan(&success); err != nil {
return err
}
if success {
p.isLocked = true
return nil
}
return database.ErrLocked
}
func (p *Postgres) Unlock() error {
if !p.isLocked {
return nil
}
aid, err := p.generateAdvisoryLockId()
if err != nil {
return err
}
if _, err := p.db.Exec("SELECT pg_advisory_unlock($1)", aid); err != nil {
return err
}
p.isLocked = false
return nil
}
func (p *Postgres) Run(version int, migration io.Reader) error {
if migration == nil {
// just apply version
return p.saveVersion(version)
}
mgr, err := ioutil.ReadAll(migration)
if err != nil {
return err
}
// it would be nice to be able to wrap the migration into the transaction, too
// unfortunately things like `CREATE INDEX CONCURRENTLY` aren't possible in a
// transaction. so if something fails between running the migration, and
// storing the latest migration version in the version table, we alert the user
// who then needs to manually fix.
// TODO: two phase commit?
if _, err := p.db.Exec(string(mgr[:])); err != nil {
return err
}
return p.saveVersion(version)
}
func (p *Postgres) saveVersion(version int) error {
tx, err := p.db.Begin()
if err != nil {
return err // TODO: warn user
}
if _, err := p.db.Exec("TRUNCATE " + tableName + ""); err != nil {
tx.Rollback()
return err // TODO: warn user
}
if version >= 0 {
if _, err := p.db.Exec("INSERT INTO "+tableName+" (version) VALUES ($1)", version); err != nil {
tx.Rollback()
return err // TODO: warn user
}
}
if err := tx.Commit(); err != nil {
return err // TODO: warn user
}
return nil
}
func (p *Postgres) Version() (int, error) {
var version uint64
err := p.db.QueryRow("SELECT version FROM " + tableName + " ORDER BY version DESC LIMIT 1").Scan(&version)
switch {
case err == sql.ErrNoRows:
return database.NilVersion, nil
case err != nil:
if e, ok := err.(*pq.Error); ok {
if e.Code.Name() == "undefined_table" {
return database.NilVersion, nil
}
}
return 0, err
default:
return int(version), nil
}
}
func (p *Postgres) Drop() error {
if _, err := p.db.Exec("DROP SCHEMA public cascade "); err != nil {
return err
}
if _, err := p.db.Exec("CREATE SCHEMA public"); err != nil {
return err
}
if err := p.ensureVersionTable(); err != nil {
return err
}
return nil
}
func (p *Postgres) ensureVersionTable() error {
r := p.db.QueryRow("SELECT count(*) FROM information_schema.tables WHERE table_name = $1 AND table_schema = (SELECT current_schema())", tableName)
c := 0
if err := r.Scan(&c); err != nil {
return err
}
if c > 0 {
return nil
}
if _, err := p.db.Exec("CREATE TABLE IF NOT EXISTS " + tableName + " (version bigint not null primary key);"); err != nil {
return err
}
return nil
}
const AdvisoryLockIdSalt uint = 1486364155
// inspired by rails migrations, see https://goo.gl/8o9bCT
func (p *Postgres) generateAdvisoryLockId() (string, error) {
if p.url == nil {
return "", ErrNoDatabaseName
}
dbname := p.url.Path
if len(dbname) == 0 {
return "", ErrNoDatabaseName
}
sum := crc32.ChecksumIEEE([]byte(dbname))
sum = sum * uint32(AdvisoryLockIdSalt)
return fmt.Sprintf("%v", sum), nil
}