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migrate.go
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migrate.go
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package migrate
import (
"database/sql"
"log"
)
const migrationTableStmt = `
CREATE TABLE IF NOT EXISTS migration (
revision BIGINT PRIMARY KEY
)
`
const migrationSelectStmt = `
SELECT revision FROM migration
WHERE revision = ?
`
const migrationSelectMaxStmt = `
SELECT max(revision) FROM migration
`
const insertRevisionStmt = `
INSERT INTO migration (revision) VALUES (?)
`
const deleteRevisionStmt = `
DELETE FROM migration where revision = ?
`
type Revision interface {
Up(mg *MigrationDriver) error
Down(mg *MigrationDriver) error
Revision() int64
}
type Migration struct {
db *sql.DB
revs []Revision
}
var Driver DriverBuilder
func New(db *sql.DB) *Migration {
return &Migration{db: db}
}
// Add the Revision to the list of migrations.
func (m *Migration) Add(rev ...Revision) *Migration {
m.revs = append(m.revs, rev...)
return m
}
// Migrate executes the full list of migrations.
func (m *Migration) Migrate() error {
var target int64
if len(m.revs) > 0 {
// get the last revision number in
// the list. This is what we'll
// migrate toward.
target = m.revs[len(m.revs)-1].Revision()
}
return m.MigrateTo(target)
}
// MigrateTo executes all database migration until
// you are at the specified revision number.
// If the revision number is less than the
// current revision, then we will downgrade.
func (m *Migration) MigrateTo(target int64) error {
// make sure the migration table is created.
if _, err := m.db.Exec(migrationTableStmt); err != nil {
return err
}
// get the current revision
var current int64
m.db.QueryRow(migrationSelectMaxStmt).Scan(¤t)
// already up to date
if current == target {
log.Println("Database already up-to-date.")
return nil
}
// should we downgrade?
if target < current {
return m.down(target, current)
}
// else upgrade
return m.up(target, current)
}
func (m *Migration) up(target, current int64) error {
// create the database transaction
tx, err := m.db.Begin()
if err != nil {
return err
}
mg := Driver(tx)
// loop through and execute revisions
for _, rev := range m.revs {
if rev.Revision() > current && rev.Revision() <= target {
current = rev.Revision()
// execute the revision Upgrade.
if err := rev.Up(mg); err != nil {
log.Printf("Failed to upgrade to Revision Number %v\n", current)
log.Println(err)
return tx.Rollback()
}
// update the revision number in the database
if _, err := tx.Exec(insertRevisionStmt, current); err != nil {
log.Printf("Failed to register Revision Number %v\n", current)
log.Println(err)
return tx.Rollback()
}
log.Printf("Successfully upgraded to Revision %v\n", current)
}
}
return tx.Commit()
}
func (m *Migration) down(target, current int64) error {
// create the database transaction
tx, err := m.db.Begin()
if err != nil {
return err
}
mg := Driver(tx)
// reverse the list of revisions
revs := []Revision{}
for _, rev := range m.revs {
revs = append([]Revision{rev}, revs...)
}
// loop through the (reversed) list of
// revisions and execute.
for _, rev := range revs {
if rev.Revision() > target {
current = rev.Revision()
// execute the revision Upgrade.
if err := rev.Down(mg); err != nil {
log.Printf("Failed to downgrade from Revision Number %v\n", current)
log.Println(err)
return tx.Rollback()
}
// update the revision number in the database
if _, err := tx.Exec(deleteRevisionStmt, current); err != nil {
log.Printf("Failed to unregistser Revision Number %v\n", current)
log.Println(err)
return tx.Rollback()
}
log.Printf("Successfully downgraded from Revision %v\n", current)
}
}
return tx.Commit()
}