GreenDAO是一款非要流行的android平台上的数据库框架，性能优秀，代码简洁。
初始化数据库模型代码的时候需要使用java项目生成代码，依赖的jar包已经上传到我的资源里了，下载地址如下：http://download.csdn.net/detail/fancylovejava/8859203
项目开发中用到的就是GreenDAO数据库框架，需要进行数据库版本升级。
其实数据库版本升级比较麻烦的就是数据的迁移，data migration。
数据库版本升级有很多方法，按不同需求来处理。
本质上是去执行sql语句去创建临时数据表，然后迁移数据，修改临时表名等。
数据版本升级，为了便于维护代码可以先定义一个抽象类
public abstract class AbstractMigratorHelper { public abstract void onUpgrade(SQLiteDatabase db); }
然后让自己更新数据库逻辑的类继承这个类
public class DBMigrationHelper6 extends AbstractMigratorHelper { /* Upgrade from DB schema 6 to schema 7 , version numbers are just examples*/ public void onUpgrade(SQLiteDatabase db) { /* Create a temporal table where you will copy all the data from the previous table that you need to modify with a non supported sqlite operation */ db.execSQL("CREATE TABLE " + "'post2' (" + // "'_id' INTEGER PRIMARY KEY ," + // 0: id "'POST_ID' INTEGER UNIQUE ," + // 1: postId "'USER_ID' INTEGER," + // 2: userId "'VERSION' INTEGER," + // 3: version "'TYPE' TEXT," + // 4: type "'MAGAZINE_ID' TEXT NOT NULL ," + // 5: magazineId "'SERVER_TIMESTAMP' INTEGER," + // 6: serverTimestamp "'CLIENT_TIMESTAMP' INTEGER," + // 7: clientTimestamp "'MAGAZINE_REFERENCE' TEXT NOT NULL ," + // 8: magazineReference "'POST_CONTENT' TEXT);"); // 9: postContent /* Copy the data from one table to the new one */ db.execSQL("INSERT INTO post2 (_id, POST_ID, USER_ID, VERSION, TYPE, MAGAZINE_ID, SERVER_TIMESTAMP, CLIENT_TIMESTAMP, MAGAZINE_REFERENCE, POST_CONTENT)" + " SELECT _id, POST_ID, USER_ID, VERSION, TYPE, MAGAZINE_ID, SERVER_TIMESTAMP, CLIENT_TIMESTAMP, MAGAZINE_REFERENCE, POST_CONTENT FROM post;"); /* Delete the previous table */ db.execSQL("DROP TABLE post"); /* Rename the just created table to the one that I have just deleted */ db.execSQL("ALTER TABLE post2 RENAME TO post"); /* Add Index/es if you want them */ db.execSQL("CREATE INDEX " + "IDX_post_USER_ID ON post" + " (USER_ID);"); //Example sql statement db.execSQL("ALTER TABLE user ADD COLUMN USERNAME TEXT"); } }
最后在OpenHelper方法里的OnUpgrade方法里面处理，这里方法调用的比较巧妙，借用国外大牛的代码复制下。
public static class UpgradeHelper extends OpenHelper { public UpgradeHelper(Context context, String name, CursorFactory factory) { super(context, name, factory); } /** * Here is where the calls to upgrade are executed */ @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { /* i represent the version where the user is now and the class named with this number implies that is upgrading from i to i++ schema */ for (int i = oldVersion; i < newVersion; i++) { try { /* New instance of the class that migrates from i version to i++ version named DBMigratorHelper{version that the db has on this moment} */ AbstractMigratorHelper migratorHelper = (AbstractMigratorHelper) Class.forName("com.nameofyourpackage.persistence.MigrationHelpers.DBMigrationHelper" + i).newInstance(); if (migratorHelper != null) { /* Upgrade de db */ migratorHelper.onUpgrade(db); } } catch (ClassNotFoundException | ClassCastException | IllegalAccessException | InstantiationException e) { Log.e(TAG, "Could not migrate from schema from schema: " + i + " to " + i++); /* If something fail prevent the DB to be updated to future version if the previous version has not been upgraded successfully */ break; } } } }
上面已经做了数据的迁移，国外有个大牛封装的代码摘抄下来：
/** * Created by pokawa on 18/05/15. */ 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(SQLiteDatabase db, Class<? extends AbstractDao<?, ?>>... daoClasses) { generateTempTables(db, daoClasses); DaoMaster.dropAllTables(db, true); DaoMaster.createAllTables(db, false); restoreData(db, daoClasses); } private void generateTempTables(SQLiteDatabase 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) { Crashlytics.logException(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(SQLiteDatabase 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())); Crashlytics.logException(exception); throw exception; } private static List<String> getColumns(SQLiteDatabase 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; } }
然后在OnUpgrade方法里面去调用
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { Log.i("greenDAO", "Upgrading schema from version " + oldVersion + " to " + newVersion + " by migrating all tables data"); MigrationHelper.getInstance().migrate(db, UserDao.class, ItemDao.class); }
上面代码全是干货，记录下来以备不时之需！