greenDao数据库升级

在使用greenDao作为本地数据库操作时，会发现数据库升级无从下手，于是从爆栈网的答案中整理出了以下数据库升级方式的代码，感谢国外网友。

public class MigrationHelper {    private static final String CONVERSION_CLASS_NOT_FOUND_EXCEPTION =        "MIGRATION HELPER - CLASS DOESN'T MATCH WITH THE CURRENT PARAMETERS";    private static MigrationHelper instance;    public static MigrationHelper getInstance() {        if (instance == null) {            instance = new MigrationHelper();        }        return instance;    }    public void migrate(Database db, Class<? extends AbstractDao<?, ?>>... daoClasses) {        generateTempTables(db, daoClasses);        DaoMaster.dropAllTables(db, true);        DaoMaster.createAllTables(db, false);        restoreData(db, daoClasses);    }    private void generateTempTables(Database db, Class<? extends AbstractDao<?, ?>>... daoClasses) {        for (int i = 0; i < daoClasses.length; i++) {            DaoConfig daoConfig = new DaoConfig(db, daoClasses[i]);            String divider = "";            String tableName = daoConfig.tablename;            String tempTableName = daoConfig.tablename.concat("_TEMP");            ArrayList<String> properties = new ArrayList<>();            StringBuilder createTableStringBuilder = new StringBuilder();            createTableStringBuilder.append("CREATE TABLE ").append(tempTableName).append(" (");            for (int j = 0; j < daoConfig.properties.length; j++) {                String columnName = daoConfig.properties[j].columnName;                if (getColumns(db, tableName).contains(columnName)) {                    properties.add(columnName);                    String type = null;                    try {                        type = getTypeByClass(daoConfig.properties[j].type);                    } catch (Exception exception) {                    }                    createTableStringBuilder.append(divider).append(columnName).append(" ").append(type);                    if (daoConfig.properties[j].primaryKey) {                        createTableStringBuilder.append(" PRIMARY KEY");                    }                    divider = ",";                }            }            createTableStringBuilder.append(");");            db.execSQL(createTableStringBuilder.toString());            StringBuilder insertTableStringBuilder = new StringBuilder();            insertTableStringBuilder.append("INSERT INTO ").append(tempTableName).append(" (");            insertTableStringBuilder.append(TextUtils.join(",", properties));            insertTableStringBuilder.append(") SELECT ");            insertTableStringBuilder.append(TextUtils.join(",", properties));            insertTableStringBuilder.append(" FROM ").append(tableName).append(";");            db.execSQL(insertTableStringBuilder.toString());        }    }    private 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");            ArrayList<String> properties = new ArrayList();            for (int j = 0; j < daoConfig.properties.length; j++) {                String columnName = daoConfig.properties[j].columnName;                if (getColumns(db, tempTableName).contains(columnName)) {                    properties.add(columnName);                }            }            StringBuilder insertTableStringBuilder = new StringBuilder();            insertTableStringBuilder.append("INSERT INTO ").append(tableName).append(" (");            insertTableStringBuilder.append(TextUtils.join(",", properties));            insertTableStringBuilder.append(") SELECT ");            insertTableStringBuilder.append(TextUtils.join(",", properties));            insertTableStringBuilder.append(" FROM ").append(tempTableName).append(";");            StringBuilder dropTableStringBuilder = new StringBuilder();            dropTableStringBuilder.append("DROP TABLE ").append(tempTableName);            db.execSQL(insertTableStringBuilder.toString());            db.execSQL(dropTableStringBuilder.toString());        }    }    private String getTypeByClass(Class<?> type) throws Exception {        if (type.equals(String.class)) {            return "TEXT";        }        if (type.equals(Long.class) || type.equals(Integer.class) || type.equals(long.class)) {            return "INTEGER";        }        if (type.equals(Boolean.class)) {            return "BOOLEAN";        }        Exception exception =            new Exception(CONVERSION_CLASS_NOT_FOUND_EXCEPTION.concat(" - Class: ").concat(type.toString()));        throw exception;    }    private static List<String> getColumns(Database db, String tableName) {        List<String> columns = new ArrayList<>();        Cursor cursor = null;        try {            cursor = db.rawQuery("SELECT * FROM " + tableName + " limit 1", null);            if (cursor != null) {                columns = new ArrayList<>(Arrays.asList(cursor.getColumnNames()));            }        } catch (Exception e) {            Log.v(tableName, e.getMessage(), e);            e.printStackTrace();        } finally {            if (cursor != null) cursor.close();        }        return columns;    }}

使用方式：

public class MyOpenHelper extends DaoMaster.OpenHelper {    public MyOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory) {        super(context, name, factory);    }    @Override public void onUpgrade(Database db, int oldVersion, int newVersion) {        Log.i("greenDAO",            "Upgrading schema from version " + oldVersion + " to " + newVersion + " by migrating all tables data");        // 第二个参数为要升级的Dao文件.        MigrationHelper.getInstance().migrate(db, xxxDao.class);    }}