使用場景：使用GreenDao操作資料庫，必然涉及到資料庫版本升級：增加表、增加欄位。

greendao {
    schemaVersion 1//資料庫版本號}

他的實現思路是：

• 1、建立臨時表temporary，將原先表資料遷移過去
• 2、刪除所有原表
• 3、建立新表
• 4、將temporary表資料複製到新表，最後將temporary表刪除

建立一個類MigrationHelper：

/**
 * 
 * please call {@link #migrate(SQLiteDatabase, Class[])}
 * 
 */
public final class MigrationHelper {

    public static boolean DEBUG = false;
    private static String TAG = "MigrationHelper";
    private static final String SQLITE_MASTER = "sqlite_master";
    private static final 
 
String SQLITE_TEMP_MASTER = "sqlite_temp_master";
    public static void migrate(SQLiteDatabase db, Class<? extends AbstractDao<?, ?>>... daoClasses) {
        Database database = new StandardDatabase(db);
printLog("【The Old Database Version】" + db.getVersion());
printLog("【Generate temp table】start"
 
);
generateTempTables(database, daoClasses);
printLog("【Generate temp table】complete");
dropAllTables(database, true, daoClasses);
createAllTables(database, false, daoClasses);
printLog("【Restore data】start");
restoreData(database, daoClasses);
printLog("【Restore data】complete");
}

    private static void generateTempTables(Database db, Class<? extends AbstractDao<?, ?>>... daoClasses) {
        for (int i = 0; i < daoClasses.length; i++) {
            String tempTableName = null;
DaoConfig daoConfig = new DaoConfig(db, daoClasses[i]);
String tableName = daoConfig.tablename;
            if (!isTableExists(db, false, tableName)) {
                printLog("【New Table】" + tableName);
                continue;
}
            try {
                tempTableName = daoConfig.tablename.concat("_TEMP");
StringBuilder dropTableStringBuilder = new StringBuilder();
dropTableStringBuilder.append("DROP TABLE IF EXISTS ").append(tempTableName).append(";");
db.execSQL(dropTableStringBuilder.toString());
StringBuilder insertTableStringBuilder = new StringBuilder();
insertTableStringBuilder.append("CREATE TEMPORARY TABLE ").append(tempTableName);
insertTableStringBuilder.append(" AS SELECT * FROM ").append(tableName).append(";");
db.execSQL(insertTableStringBuilder.toString());
printLog("【Table】" + tableName +"\n ---Columns-->"+getColumnsStr(daoConfig));
printLog("【Generate temp table】" + tempTableName);
} catch (SQLException e) {
                Log.e(TAG, "【Failed to generate temp table】" + tempTableName, e);
}
        }
    }

    private static boolean isTableExists(Database db, boolean isTemp, String tableName) {
        if (db == null || TextUtils.isEmpty(tableName)) {
            return false;
}
        String dbName = isTemp ? SQLITE_TEMP_MASTER : SQLITE_MASTER;
String sql = "SELECT COUNT(*) FROM " + dbName + " WHERE type = ? AND name = ?";
Cursor cursor=null;
        int count = 0;
        try {
            cursor = db.rawQuery(sql, new String[]{"table", tableName});
            if (cursor == null || !cursor.moveToFirst()) {
                return false;
}
            count = cursor.getInt(0);
} catch (Exception e) {
            e.printStackTrace();
} finally {
            if (cursor != null)
                cursor.close();
}
        return count > 0;
}


    private static String getColumnsStr(DaoConfig daoConfig) {
        if (daoConfig == null) {
            return "no columns";
}
        StringBuilder builder = new StringBuilder();
        for (int i = 0; i < daoConfig.allColumns.length; i++) {
            builder.append(daoConfig.allColumns[i]);
builder.append(",");
}
        if (builder.length() > 0) {
            builder.deleteCharAt(builder.length() - 1);
}
        return builder.toString();
}


    private static void dropAllTables(Database db, boolean ifExists, @NonNull Class<? extends AbstractDao<?, ?>>... daoClasses) {
        reflectMethod(db, "dropTable", ifExists, daoClasses);
printLog("【Drop all table】");
}

    private static void createAllTables(Database db, boolean ifNotExists, @NonNull Class<? extends AbstractDao<?, ?>>... daoClasses) {
        reflectMethod(db, "createTable", ifNotExists, daoClasses);
printLog("【Create all table】");
}

    /**
     * dao class already define the sql exec method, so just invoke it
     */
private static void reflectMethod(Database db, String methodName, boolean isExists, @NonNull Class<? extends AbstractDao<?, ?>>... daoClasses) {
        if (daoClasses.length < 1) {
            return;
}
        try {
            for (Class cls : daoClasses) {
                Method method = cls.getDeclaredMethod(methodName, Database.class, boolean.class);
method.invoke(null, db, isExists);
}
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
} catch (InvocationTargetException e) {
            e.printStackTrace();
} catch (IllegalAccessException e) {
            e.printStackTrace();
}
    }

    private static void restoreData(Database db, Class<? extends AbstractDao<?, ?>>... daoClasses) {
        for (int i = 0; i < daoClasses.length; i++) {
            DaoConfig daoConfig = new DaoConfig(db, daoClasses[i]);
String tableName = daoConfig.tablename;
String tempTableName = daoConfig.tablename.concat("_TEMP");
            if (!isTableExists(db, true, tempTableName)) {
                continue;
}

            try {
                // get all columns from tempTable, take careful to use the columns list
List<String> columns = getColumns(db, tempTableName);
ArrayList<String> properties = new ArrayList<>(columns.size());
                for (int j = 0; j < daoConfig.properties.length; j++) {
                    String columnName = daoConfig.properties[j].columnName;
                    if (columns.contains(columnName)) {
                        properties.add(columnName);
}
                }
                if (properties.size() > 0) {
                    final String columnSQL = TextUtils.join(",", properties);
StringBuilder insertTableStringBuilder = new StringBuilder();
insertTableStringBuilder.append("INSERT INTO ").append(tableName).append(" (");
insertTableStringBuilder.append(columnSQL);
insertTableStringBuilder.append(") SELECT ");
insertTableStringBuilder.append(columnSQL);
insertTableStringBuilder.append(" FROM ").append(tempTableName).append(";");
db.execSQL(insertTableStringBuilder.toString());
printLog("【Restore data】 to " + tableName);
}
                StringBuilder dropTableStringBuilder = new StringBuilder();
dropTableStringBuilder.append("DROP TABLE ").append(tempTableName);
db.execSQL(dropTableStringBuilder.toString());
printLog("【Drop temp table】" + tempTableName);
} catch (SQLException e) {
                Log.e(TAG, "【Failed to restore data from temp table 】" + tempTableName, e);
}
        }
    }

    private static List<String> getColumns(Database db, String tableName) {
        List<String> columns = null;
Cursor cursor = null;
        try {
            cursor = db.rawQuery("SELECT * FROM " + tableName + " limit 0", null);
            if (null != cursor && cursor.getColumnCount() > 0) {
                columns = Arrays.asList(cursor.getColumnNames());
}
        } catch (Exception e) {
            e.printStackTrace();
} finally {
            if (cursor != null)
                cursor.close();
            if (null == columns)
                columns = new ArrayList<>();
}
        return columns;
}

    private static void printLog(String info){
        if(DEBUG){
            Log.d(TAG, info);
}
    }

}

/**
 * 自定義一個OpenHelper類，為以後資料庫升級時使用
 * Created by KingsleyCheng on 2017/5/18.
 */
public class MySQLiteOpenHelper extends DaoMaster.OpenHelper {

    public MySQLiteOpenHelper(Context context, String name) {
        super(context, name);
}

    public MySQLiteOpenHelper(Context context, String name,
                            SQLiteDatabase.CursorFactory factory) {
        super(context, name, factory);
}

    @Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        MigrationHelper.migrate(db,ProjectListDao.classUserListDao.class);//資料版本變更才會執行
}

}

在DaoMaster類的onUpgrade方法新增如下程式碼即可，引數為所有的Dao類：

 @Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        MigrationHelper.migrate(db,“所有的Dao類”);//資料版本變更才會執行
}