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44ffb70813
Also add some comments.
167 lines
3.6 KiB
Go
167 lines
3.6 KiB
Go
package migrate
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import (
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"database/sql"
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"log"
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)
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const migrationTableStmt = `
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CREATE TABLE IF NOT EXISTS migration (
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revision BIGINT PRIMARY KEY
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)
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`
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const migrationSelectStmt = `
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SELECT revision FROM migration
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WHERE revision = ?
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`
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const migrationSelectMaxStmt = `
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SELECT max(revision) FROM migration
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`
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const insertRevisionStmt = `
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INSERT INTO migration (revision) VALUES (?)
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`
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const deleteRevisionStmt = `
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DELETE FROM migration where revision = ?
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`
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type Revision interface {
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Up(mg *MigrationDriver) error
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Down(mg *MigrationDriver) error
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Revision() int64
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}
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type Migration struct {
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db *sql.DB
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revs []Revision
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}
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var Driver DriverBuilder
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func New(db *sql.DB) *Migration {
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return &Migration{db: db}
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}
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// Add the Revision to the list of migrations.
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func (m *Migration) Add(rev ...Revision) *Migration {
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m.revs = append(m.revs, rev...)
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return m
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}
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// Migrate executes the full list of migrations.
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func (m *Migration) Migrate() error {
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var target int64
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if len(m.revs) > 0 {
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// get the last revision number in
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// the list. This is what we'll
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// migrate toward.
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target = m.revs[len(m.revs)-1].Revision()
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}
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return m.MigrateTo(target)
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}
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// MigrateTo executes all database migration until
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// you are at the specified revision number.
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// If the revision number is less than the
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// current revision, then we will downgrade.
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func (m *Migration) MigrateTo(target int64) error {
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// make sure the migration table is created.
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if _, err := m.db.Exec(migrationTableStmt); err != nil {
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return err
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}
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// get the current revision
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var current int64
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m.db.QueryRow(migrationSelectMaxStmt).Scan(¤t)
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// already up to date
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if current == target {
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log.Println("Database already up-to-date.")
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return nil
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}
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// should we downgrade?
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if target < current {
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return m.down(target, current)
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}
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// else upgrade
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return m.up(target, current)
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}
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func (m *Migration) up(target, current int64) error {
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// create the database transaction
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tx, err := m.db.Begin()
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if err != nil {
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return err
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}
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mg := Driver(tx)
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// loop through and execute revisions
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for _, rev := range m.revs {
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if rev.Revision() > current && rev.Revision() <= target {
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current = rev.Revision()
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// execute the revision Upgrade.
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if err := rev.Up(mg); err != nil {
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log.Printf("Failed to upgrade to Revision Number %v\n", current)
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log.Println(err)
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return tx.Rollback()
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}
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// update the revision number in the database
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if _, err := tx.Exec(insertRevisionStmt, current); err != nil {
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log.Printf("Failed to register Revision Number %v\n", current)
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log.Println(err)
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return tx.Rollback()
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}
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log.Printf("Successfully upgraded to Revision %v\n", current)
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}
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}
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return tx.Commit()
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}
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func (m *Migration) down(target, current int64) error {
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// create the database transaction
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tx, err := m.db.Begin()
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if err != nil {
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return err
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}
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mg := Driver(tx)
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// reverse the list of revisions
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revs := []Revision{}
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for _, rev := range m.revs {
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revs = append([]Revision{rev}, revs...)
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}
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// loop through the (reversed) list of
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// revisions and execute.
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for _, rev := range revs {
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if rev.Revision() > target {
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current = rev.Revision()
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// execute the revision Upgrade.
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if err := rev.Down(mg); err != nil {
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log.Printf("Failed to downgrade from Revision Number %v\n", current)
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log.Println(err)
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return tx.Rollback()
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}
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// update the revision number in the database
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if _, err := tx.Exec(deleteRevisionStmt, current); err != nil {
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log.Printf("Failed to unregistser Revision Number %v\n", current)
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log.Println(err)
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return tx.Rollback()
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}
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log.Printf("Successfully downgraded from Revision %v\n", current)
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}
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}
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return tx.Commit()
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}
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