From 8d135d7b228f9f746e384764dd27b05729c739a8 Mon Sep 17 00:00:00 2001
From: Brad Rydzewski <brad.rydzewski@gmail.com>
Date: Mon, 10 Feb 2014 03:03:22 -0700
Subject: [PATCH] package for database migrations

---
 pkg/database/migrate/migrate.go          | 182 +++++++++++++++++++++++
 pkg/database/migrate/migrate_20150209.go |  19 +++
 2 files changed, 201 insertions(+)
 create mode 100644 pkg/database/migrate/migrate.go
 create mode 100644 pkg/database/migrate/migrate_20150209.go

diff --git a/pkg/database/migrate/migrate.go b/pkg/database/migrate/migrate.go
new file mode 100644
index 00000000..715596ad
--- /dev/null
+++ b/pkg/database/migrate/migrate.go
@@ -0,0 +1,182 @@
+// Usage
+//    migrate.To(2)
+//    	.Add(Version_1)
+//    	.Add(Version_2)
+//    	.Add(Version_3)
+//    	.Exec(db)
+//
+//    migrate.ToLatest()
+//    	.Add(Version_1)
+//    	.Add(Version_2)
+//    	.Add(Version_3)
+//    	.SetDialect(migrate.MySQL)
+//    	.Exec(db)
+//
+//    migrate.ToLatest()
+//    	.Add(Version_1)
+//    	.Add(Version_2)
+//    	.Add(Version_3)
+//		.Backup(path)
+//		.Exec()
+
+package migrate
+
+import (
+	"database/sql"
+	"log"
+)
+
+const migrationTableStmt = `
+CREATE TABLE IF NOT EXISTS migration (
+	revision NUMBER 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(tx *sql.Tx) error
+	Down(tx *sql.Tx) error
+	Revision() int64
+}
+
+type Migration struct {
+	db   *sql.DB
+	revs []Revision
+}
+
+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
+}
+
+// Execute 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)
+}
+
+// Execute 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(&current)
+
+	// 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
+	}
+
+	// loop through and execute revisions
+	for _, rev := range m.revs {
+		if rev.Revision() >= target {
+			current = rev.Revision()
+			// execute the revision Upgrade.
+			if err := rev.Up(tx); 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
+	}
+
+	// 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(tx); err != nil {
+				log.Printf("Failed to downgrade to 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 to Revision %v\n", current)
+		}
+	}
+
+	return tx.Commit()
+}
diff --git a/pkg/database/migrate/migrate_20150209.go b/pkg/database/migrate/migrate_20150209.go
new file mode 100644
index 00000000..92164eb8
--- /dev/null
+++ b/pkg/database/migrate/migrate_20150209.go
@@ -0,0 +1,19 @@
+package migrate
+
+import (
+	"database/sql"
+)
+
+type Change_20150209 struct{}
+
+func (Change_20150209) Up(tx *sql.Tx) error {
+	return nil
+}
+
+func (Change_20150209) Down(tx *sql.Tx) error {
+	return nil
+}
+
+func (Change_20150209) Revision() int64 {
+	return 20150209
+}