1. APP開發(fā)期間的數(shù)據(jù)庫

在上一篇文章中封裝了GreenDaoManager中有個構(gòu)造方法如下:

private GreenDaoManager(){
        if (mInstance == null) {
//            DaoMaster.DevOpenHelper devOpenHelper = new
//                    DaoMaster.DevOpenHelper(MyApplication.getContext(), "database_name", null);//此處openhelper為自動生成開發(fā)所使用，發(fā)布版本需自定義
            MySQLiteOpenHelper devOpenHelper = new
                    MySQLiteOpenHelper(new GreenDaoContext(), "database_name.db", null);//GreenDaoContext為創(chuàng)建數(shù)據(jù)庫路徑使用
            mDaoMaster = new DaoMaster(devOpenHelper.getWritableDatabase());
            mDaoSession = mDaoMaster.newSession();
        }
    }

其中注釋掉的兩行代碼中：

DaoMaster.DevOpenHelper devOpenHelper = new
DaoMaster.DevOpenHelper(MyApplication.getContext(), "database_name", null);//此處DevOpenHelper 為自動生成開發(fā)所使用，發(fā)布版本需自定義

其中的MyApplication.getContext()上下文表示了數(shù)據(jù)庫存儲路徑為手機內(nèi)存。這里的DevOpenHelper即為DaoMaster中自動生成代碼，完整代碼如下：

/** * WARNING: Drops all table on Upgrade! Use only during development. */
public static class DevOpenHelper extends OpenHelper {    
  public DevOpenHelper(Context context, String name, CursorFactory factory) {
             super(context, name, factory);    
  }    
  @Override    
  public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {            
        Log.i("greenDAO", "Upgrading schema from version " + oldVersion + " to " + newVersion + " by dropping all tables");        
        dropAllTables(db, true);        
        onCreate(db);    
  }
}

注意看第一行注釋：WARNING: Drops all table on Upgrade! Use only during development.
數(shù)據(jù)庫升級的話，會刪除所有表,然后重新創(chuàng)建。這種方式在開發(fā)期間，APP還沒有上線之前是可以的。

當APP上線后，我們不能使用這種方式，因為這樣會導致已經(jīng)存在的數(shù)據(jù)會被刪除。

2. APP上線后,數(shù)據(jù)庫升級

我們需要重寫一個類MySQLiteOpenHelper實現(xiàn)OpenHelper.

1. 需要自己實現(xiàn)了onUpgrade方法來自定義升級過程。
2. 當然升級過程中也要修改DaoMaster.SCHEMA_VERSION
3. 當DaoMaster.SCHEMA_VERSION跟你當前數(shù)據(jù)庫的版本比較后,會根據(jù)你當前數(shù)據(jù)庫的版本，然后進行升級。
4. 關(guān)鍵代碼onUpgrade方法,會比較新數(shù)據(jù)庫和舊數(shù)據(jù)庫的版本,然后執(zhí)行相應的sql升級：

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) {
        //數(shù)據(jù)遷移模塊
        MigrationHelper.migrate(db,
                UserDao.class,
                ProfessionDao.class,
                LTestDao.class);
    }
}

數(shù)據(jù)庫升級不外乎兩種情況：
　 1.修改表結(jié)構(gòu)。
　 2.添加新表。

針對onUpgrade中的實現(xiàn)方法可以采用兩種不同策略:（稍后都會提供兩種策略的代碼實現(xiàn)，下面主要講述第二種數(shù)據(jù)遷移實現(xiàn)方式）
　1.逐級版本迭代升級，比如當前版本為1，最新版本為3，此方案就是先從1-->2-->3.
　2.把數(shù)據(jù)庫中的數(shù)據(jù)備份，然后全刪數(shù)據(jù)庫，再重新創(chuàng)建新的數(shù)據(jù)庫，把備份數(shù)據(jù)導入。此方案直接從１-->3。

3. 數(shù)據(jù)遷移（數(shù)據(jù)庫備份）的具體實現(xiàn)

1. android上面對的數(shù)據(jù)庫基本上就是輕量級數(shù)據(jù)庫sqlite,首先我們需要了解一些后面需要用到的數(shù)據(jù)庫操作語句：

• 判斷sqlite表是否存在
  SELECT * FROM sqlite_master WHERE type='table' AND name='tempTableName';
• sqlite判斷臨時表是否存在
  SELECT * FROM sqlite_temp_master WHERE type='table' AND name='tempTableName';
• sqlite創(chuàng)建表tableName的臨時表
  create temporary table tempTableName as select * from tableName;
• 刪除臨時表
  drop table tempTableName;

2. sqlite的系統(tǒng)表sqlite_master、臨時表sqlite_temp_master
   SQLite數(shù)據(jù)庫中一個特殊的名叫 SQLITE_MASTER上執(zhí)行一個SELECT查詢以獲得所有表的索引。每一個 SQLite 數(shù)據(jù)庫都有一個叫 SQLITE_MASTER的表， 它定義數(shù)據(jù)庫的模式。 SQLITE_MASTER表看起來如下：

CREATE TABLE sqlite_master ( 
type TEXT, 
name TEXT, 
tbl_name TEXT, 
rootpage INTEGER, 
sql TEXT 
); 

type 字段永遠是 ‘table’，name 字段永遠是對應表的名字。所以，要獲得數(shù)據(jù)庫中所有表的列表， 使用下列SELECT語句：

SELECT name FROM sqlite_master 
WHERE type=’table’ 
ORDER BY name; 

對于索引，type 等于 ‘index’, name 則是索引的名字，tbl_name 是該索引所屬的表的名字。 不管是表還是索引，sql 字段是原先用 CREATE TABLE 或 CREATE INDEX 語句創(chuàng)建它們時的命令文本。對于自動創(chuàng)建的索引（用來實現(xiàn) PRIMARY KEY 或 UNIQUE 約束），sql字段為NULL。
SQLITE_MASTER 表是只讀的。不能對它使用 UPDATE、INSERT 或 DELETE。 它會被 CREATE TABLE、CREATE INDEX、DROP TABLE 和 DROP INDEX 命令自動更新。
臨時表及其索引和觸發(fā)器存放在另外一個叫 SQLITE_TEMP_MASTER 的表中。SQLITE_TEMP_MASTER 跟 SQLITE_MASTER 差不多， 但它只是對于創(chuàng)建那些臨時表的應用可見。如果要獲得所有表的列表， 不管是永久的還是臨時的，可以使用類似下面的命令：

SELECT name FROM 
(SELECT * FROM sqlite_master UNION ALL 
SELECT * FROM sqlite_temp_master) 
WHERE type=’table’ 
ORDER BY name

3. 數(shù)據(jù)遷移的工具類MigrationHelper。
   public final class MigrationHelper {
   public static boolean DEBUG = true;
   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)) {//不存在系統(tǒng)表中，表明是新增表，不需要創(chuàng)建臨時表
            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);
    }
   }
   }
   

4. 設置數(shù)據(jù)庫路徑

在第一模塊中有句代碼：
MySQLiteOpenHelper devOpenHelper = new MySQLiteOpenHelper(new GreenDaoContext(), "database_name.db", null);//GreenDaoContext為創(chuàng)建數(shù)據(jù)庫路徑使用
里面有個上下文GreenDaoContext繼承了ContextWrapper,里面設置了數(shù)據(jù)庫路徑，代碼如下：

public class GreenDaoContext  extends ContextWrapper {

    private String currentUserId = "greendao";//一般用來針對一個用戶一個數(shù)據(jù)庫，以免數(shù)據(jù)混亂問題
    private Context mContext;

    public GreenDaoContext() {
        super(MyApplication.getContext());
        this.mContext = MyApplication.getContext();
//        this.currentUserId = "greendao";//初始化
    }

    /**
     * 獲得數(shù)據(jù)庫路徑，如果不存在，則創(chuàng)建對象
     *
     * @param dbName
     */
    @Override
    public File getDatabasePath(String dbName) {
        String dbDir = CommonUtils.getDBPath();
        if (TextUtils.isEmpty(dbDir)){
            Log.e("SD卡管理：", "SD卡不存在，請加載SD卡");
            return null;
        }
        File baseFile = new File(dbDir);
        // 目錄不存在則自動創(chuàng)建目錄
        if (!baseFile.exists()){
            baseFile.mkdirs();
        }
        StringBuffer buffer = new StringBuffer();
        buffer.append(baseFile.getPath());
        buffer.append(File.separator);
        buffer.append(currentUserId);
        dbDir = buffer.toString();// 數(shù)據(jù)庫所在目錄
        buffer.append(File.separator);
//        buffer.append(dbName+"_"+currentUserId);//也可以采用此種方式，將用戶id與表名聯(lián)系到一塊命名
        buffer.append(dbName);
        String dbPath = buffer.toString();// 數(shù)據(jù)庫路徑
        // 判斷目錄是否存在，不存在則創(chuàng)建該目錄
        File dirFile = new File(dbDir);
        if (!dirFile.exists()){
            dirFile.mkdirs();
        }
        // 數(shù)據(jù)庫文件是否創(chuàng)建成功
        boolean isFileCreateSuccess = false;
        // 判斷文件是否存在，不存在則創(chuàng)建該文件
        File dbFile = new File(dbPath);
        if (!dbFile.exists()) {
            try {
                isFileCreateSuccess = dbFile.createNewFile();// 創(chuàng)建文件
            } catch (IOException e) {
                e.printStackTrace();
            }
        } else
            isFileCreateSuccess = true;
        // 返回數(shù)據(jù)庫文件對象
        if (isFileCreateSuccess)
            return dbFile;
        else
            return super.getDatabasePath(dbName);
    }

    /**
     * 重載這個方法，是用來打開SD卡上的數(shù)據(jù)庫的，android 2.3及以下會調(diào)用這個方法。
     *
     * @param name
     * @param mode
     * @param factory
     */
    @Override
    public SQLiteDatabase openOrCreateDatabase(String name, int mode,
                                               SQLiteDatabase.CursorFactory factory) {
        SQLiteDatabase result = SQLiteDatabase.openOrCreateDatabase(getDatabasePath(name), factory);
        return result;
    }

    /**
     * Android 4.0會調(diào)用此方法獲取數(shù)據(jù)庫。
     *
     * @param name
     * @param mode
     * @param factory
     * @param errorHandler
     * @see android.content.ContextWrapper#openOrCreateDatabase(java.lang.String, int,
     * android.database.sqlite.SQLiteDatabase.CursorFactory,
     * android.database.DatabaseErrorHandler)
     */
    @Override
    public SQLiteDatabase openOrCreateDatabase(String name, int mode, SQLiteDatabase.CursorFactory factory,
                                               DatabaseErrorHandler errorHandler) {
        SQLiteDatabase result = SQLiteDatabase.openOrCreateDatabase(getDatabasePath(name), factory);

        return result;
    }

}

OK，先到這了。。。
源碼奉上，自行參考