Add database versioning

persistence/profile.go

@@ -82,6 +82,7 @@ func NewProfile(target_dir string) (Profile, error) {
 	if err != nil {
 		return Profile{}, err
 	}
+	InitializeDatabaseVersion(db)
 
 	// Create `users.txt`
 	fmt.Printf("Creating............. %s\n", user_list_file)
@@ -183,10 +184,13 @@ func LoadProfile(profile_dir string) (Profile, error) {
 		return Profile{}, err
 	}
 
-	return Profile{
+	ret := Profile{
 		ProfileDir: profile_dir,
 		UsersList: users_list,
 		Settings: settings,
 		DB: db,
-	}, nil
+	}
+	err = ret.check_and_update_version()
+
+	return ret, err
 }

persistence/profile_test.go

@@ -105,6 +105,15 @@ func TestNewProfile(t *testing.T) {
 			t.Fatalf("Expected `%s` to be a %s, but got %s [%s]", v.filename, isdir_map(v.isDir), contents[i].Name(), isdir_map(contents[i].IsDir()))
 		}
 	}
+
+	// Check database version is initialized
+	version, err := profile.GetDatabaseVersion()
+	if err != nil {
+		panic(err)
+	}
+	if version != 0 {
+		t.Errorf("Expected database version %d, but got %d", 0, version)
+	}
 }
 
 

persistence/schema.sql

@@ -113,3 +113,7 @@ create table hashtags (rowid integer primary key,
     unique (tweet_id, text)
     foreign key(tweet_id) references tweets(id)
 );
+
+create table database_version(rowid integer primary key,
+    version_number integer not null unique
+);

persistence/versions.go

@@ -0,0 +1,90 @@
+package persistence
+
+import (
+	"fmt"
+	"database/sql"
+)
+
+
+const ENGINE_DATABASE_VERSION = 0
+
+
+type VersionMismatchError struct {
+	EngineVersion int
+	DatabaseVersion int
+}
+func (e VersionMismatchError) Error() string {
+	return fmt.Sprintf(
+`This profile was created with database schema version %d, which is newer than this application's database schema version, %d.
+Please upgrade this application to a newer version to use this profile.  Or downgrade the profile's schema version, somehow.`,
+			e.DatabaseVersion, e.EngineVersion,
+	)
+}
+
+
+/**
+ * The Nth entry is the migration that moves you from version N to version N+1
+ */
+var MIGRATIONS = []string{
+
+}
+
+/**
+ * This should only get called on a newly created Profile.
+ * Subsequent updates should change the number, not insert a new row.
+ */
+func InitializeDatabaseVersion(db *sql.DB) {
+	_, err := db.Exec("insert into database_version (version_number) values (?)", ENGINE_DATABASE_VERSION)
+	if err != nil {
+		panic(err)
+	}
+}
+
+func (p Profile) GetDatabaseVersion() (int, error) {
+	row := p.DB.QueryRow("select version_number from database_version")
+
+	var version int
+
+	err := row.Scan(&version)
+	if err != nil {
+		return 0, err
+	}
+	return version, nil
+}
+
+func (p Profile) check_and_update_version() error {
+	version, err := p.GetDatabaseVersion()
+	if err != nil {
+		return err
+	}
+
+	if version > ENGINE_DATABASE_VERSION {
+		return VersionMismatchError{ENGINE_DATABASE_VERSION, version}
+	}
+
+	if ENGINE_DATABASE_VERSION > version {
+		fmt.Printf("Upgrading database from version %d to version %d", version, ENGINE_DATABASE_VERSION)
+		p.UpgradeFromXToY(version, ENGINE_DATABASE_VERSION)
+	}
+
+	return nil
+}
+
+/**
+ * Run all the migrations from version X to version Y, and update the `database_version` table's `version_number`
+ */
+func (p Profile) UpgradeFromXToY(x int, y int) error {
+	for i := x; i < y; i++ {
+		fmt.Println(MIGRATIONS[i])
+		_, err := p.DB.Exec(MIGRATIONS[i])
+		if err != nil {
+			return err
+		}
+		_, err = p.DB.Exec("update database_version set version_number = ?", i+1)
+		if err != nil {
+			return err
+		}
+		fmt.Printf("Now at database schema version %d.\n", i + 1)
+	}
+	return nil
+}

persistence/versions_test.go

@@ -0,0 +1,33 @@
+package persistence_test
+
+import (
+	"testing"
+	"os"
+	"offline_twitter/scraper"
+	"offline_twitter/persistence"
+)
+
+func TestVersionUpgrade(t *testing.T) {
+	profile_path := "test_profiles/TestVersions"
+	if file_exists(profile_path) {
+		err := os.RemoveAll(profile_path)
+		if err != nil {
+			panic(err)
+		}
+	}
+	profile := create_or_load_profile(profile_path)
+
+	test_migration := "insert into tweets (id, user_id, text) values (21250554358298342, -1, 'awefjk')"
+	test_tweet_id := scraper.TweetID(21250554358298342)
+
+	if profile.IsTweetInDatabase(test_tweet_id) {
+		t.Fatalf("Test tweet shouldn't be in the database yet")
+	}
+
+	persistence.MIGRATIONS = append(persistence.MIGRATIONS, test_migration)
+	profile.UpgradeFromXToY(persistence.ENGINE_DATABASE_VERSION, persistence.ENGINE_DATABASE_VERSION + 1)
+
+	if !profile.IsTweetInDatabase(test_tweet_id) {
+		t.Errorf("Migration should have created the tweet, but it didn't")
+	}
+}