Initial commit

migrate.go

@@ -0,0 +1,92 @@
+// Package migrate allows you to update your database from your application
+package migrate
+
+import (
+	"database/sql"
+	"errors"
+	"fmt"
+	"strconv"
+)
+
+// Options contains all settings
+type Options struct {
+	TableName   string // Name used for version info table; defaults to DefaultTableName if not set
+	Schema      string // Schema used for version info table; For PostgreSQL, ignored if not set
+	AssetPrefix string
+}
+
+// DefaultTableName is the name used when no TableName is specified in Options
+const DefaultTableName = `version`
+
+// ErrUpdatesMissing indicates an update is missing, making it impossible to execute the migration
+var ErrUpdatesMissing = errors.New(`Missing migration files`)
+
+// ErrDatabaseNewer indicates that the database version is newer than the requested version. We throw an error because downgrades might cause dataloss
+var ErrDatabaseNewer = errors.New(`Current version is newer than the requested version`)
+
+const fileFormat = `%04d.sql`
+
+// AssetFunc is a function that returns the data for the given name
+type AssetFunc func(string) ([]byte, error)
+
+// Migrate executes
+func Migrate(db *sql.DB, version int, o Options, asset AssetFunc) error {
+	if o.TableName == `` {
+		o.TableName = DefaultTableName
+	}
+
+	table := o.TableName
+	if o.Schema != `` {
+		table = o.Schema + `.` + table
+	}
+
+	_, err := db.Exec(`CREATE TABLE IF NOT EXISTS ` + table + ` (Version integer NOT NULL PRIMARY KEY)`)
+	if err != nil {
+		return err
+	}
+
+	row := db.QueryRow(`SELECT Version FROM ` + table + ` ORDER BY Version DESC`)
+	if err != nil {
+		return err
+	}
+
+	var v int
+	err = row.Scan(&v)
+	if err != sql.ErrNoRows && err != nil {
+		return err
+	}
+
+	if v > version {
+		return ErrDatabaseNewer
+	}
+
+	tx, err := db.Begin()
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback()
+
+	for i := v + 1; i <= version; i++ {
+		asset, err := asset(fmt.Sprintf(o.AssetPrefix+fileFormat, version))
+		if err != nil {
+			return ErrUpdatesMissing
+		}
+
+		_, err = tx.Exec(string(asset))
+		if err != nil {
+			return err
+		}
+
+		_, err = tx.Exec(`INSERT INTO ` + table + ` VALUES (` + strconv.Itoa(i) + `)`)
+		if err != nil {
+			return err
+		}
+	}
+
+	err = tx.Commit()
+	if err != nil {
+		return err
+	}
+
+	return nil
+}