db: add schema table, initial schema-upgrade system

DB.go

@@ -3,6 +3,7 @@ package yatwiki
 import (
 	"database/sql"
 	"fmt"
+	"log"
 	"strings"
 	"time"
 
@@ -33,40 +34,66 @@ func NewWikiDB(dbFilePath string, compressionLevel int) (*WikiDB, error) {
 	return &wdb, nil
 }
 
+func (this *WikiDB) multiTx(stmts ...string) (err error) {
+	tx, err := this.db.Begin()
+	if err != nil {
+		return err
+	}
+
+	for _, stmt := range stmts {
+		_, err := tx.Exec(stmt)
+		if err != nil {
+			tx.Rollback()
+			return err
+		}
+	}
+
+	return tx.Commit()
+}
+
 func (this *WikiDB) assertSchema() error {
 	_, err := this.db.Exec(`
-	CREATE TABLE IF NOT EXISTS articles (
-		id			INTEGER PRIMARY KEY,
-		article		INTEGER,
-		modified	INTEGER,
-		body		BLOB,
-		author		TEXT
+	CREATE TABLE IF NOT EXISTS schema (
+		id INTEGER PRIMARY KEY
 	);`)
 	if err != nil {
 		return err
 	}
 
-	_, err = this.db.Exec(`
-	CREATE TABLE IF NOT EXISTS titles (
-		id INTEGER PRIMARY KEY,
-		title TEXT
-	);`)
-	if err != nil {
-		return err
+	// Look up current value from schema table
+	schemaLookup := this.db.QueryRow(`SELECT MAX(id) mid FROM schema`)
+	currentSchema := int64(0)
+	if err = schemaLookup.Scan(&currentSchema); err == nil {
+		// That's fine
 	}
 
-	_, err = this.db.Exec(`
-	CREATE INDEX IF NOT EXISTS articles_modified_index ON articles (modified)
-	`)
-	if err != nil {
-		return err
-	}
+	log.Printf("Found DB version %d\n", currentSchema)
 
-	_, err = this.db.Exec(`
-	CREATE INDEX IF NOT EXISTS articles_title_index ON articles (article)
-	`)
-	if err != nil {
-		return err
+	// Schema 0 ==> Schema 1
+
+	if currentSchema == 0 {
+		log.Println("Upgrading to DB version 1")
+
+		err := this.multiTx(
+			`CREATE TABLE IF NOT EXISTS articles (
+				id			INTEGER PRIMARY KEY,
+				article		INTEGER,
+				modified	INTEGER,
+				body		BLOB,
+				author		TEXT
+			);`,
+			`CREATE TABLE IF NOT EXISTS titles (
+				id INTEGER PRIMARY KEY,
+				title TEXT
+			);`,
+			`CREATE INDEX IF NOT EXISTS articles_modified_index ON articles (modified)`,
+			`CREATE INDEX IF NOT EXISTS articles_title_index ON articles (article)`,
+			`INSERT INTO schema (id) VALUES (1);`,
+		)
+		if err != nil {
+			return err
+		}
+		currentSchema = 1
 	}
 
 	return nil