（二）GreenDao3.0的数据库升级

参考网上一个工具类：

public class MigrationHelper {    /**     * 调用升级方法     * @param db     * @param daoClasses 一系列dao.class     */    public static void migrate(Database db, Class<? extends AbstractDao<?, ?>>... daoClasses) {        //1 新建临时表        generateTempTables(db, daoClasses);        //2 创建新表        createAllTables(db, false, daoClasses);        //3 临时表数据写入新表，删除临时表        restoreData(db, daoClasses);    }    /**     * 生成临时表，存储旧的表数据     * @param db     * @param daoClasses     */    private static void generateTempTables(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;            if (!checkTable(db,tableName))                continue;            String tempTableName = daoConfig.tablename.concat("_TEMP");            StringBuilder insertTableStringBuilder = new StringBuilder();            insertTableStringBuilder.append("alter table ")                    .append(tableName)                    .append(" rename to ")                    .append(tempTableName)                    .append(";");            db.execSQL(insertTableStringBuilder.toString());        }    }    /**     * 检测table是否存在     * @param db     * @param tableName     */    private static Boolean checkTable(Database db,String  tableName){        StringBuilder query = new StringBuilder();        query.append("SELECT count(*) FROM sqlite_master WHERE type='table' AND name='").append(tableName).append("'");        Cursor c = db.rawQuery(query.toString(), null);        if (c.moveToNext()){            int count = c.getInt(0);            if(count>0){                return true;            }            return false;        }        return false;    }    /**     * 删除所有旧表     * @param db     * @param ifExists     * @param daoClasses     */    private static void dropAllTables(Database db, boolean ifExists, @NonNull Class<? extends AbstractDao<?, ?>>... daoClasses) {        reflectMethod(db, "dropTable", ifExists, daoClasses);    }    /**     * 创建新的表结构     * @param db     * @param ifNotExists     * @param daoClasses     */    private static void createAllTables(Database db, boolean ifNotExists, @NonNull Class<? extends AbstractDao<?, ?>>... daoClasses) {        reflectMethod(db, "createTable", ifNotExists, daoClasses);    }    /**     * 创建根删除都在NoteDao声明了，可以直接拿过来用     * 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) {                //根据方法名，找到声明的方法                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();        }    }    /**     * 临时表的数据写入新表     * @param db     * @param daoClasses     */    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 (!checkTable(db,tempTableName))                continue;            // get all columns from tempTable, take careful to use the columns list            List<String> columns = getColumns(db, tempTableName);            //新表，临时表都包含的字段            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());            }            StringBuilder dropTableStringBuilder = new StringBuilder();            dropTableStringBuilder.append("DROP TABLE ").append(tempTableName);            db.execSQL(dropTableStringBuilder.toString());        }    }    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;    }}

（2）在自定义的帮助类中使用就可以了

public class DBHelper extends DaoMaster.OpenHelper {    public static final String DBNAME = "lenve.db";    public DBHelper(Context context) {        super(context, "lenovo.db", null);    }    @Override    public void onUpgrade(Database db, int oldVersion, int newVersion) {        super.onUpgrade(db, oldVersion, newVersion);        MigrationHelper.migrate(db,CommentDao.class);//可以写多个Dao类。    }}