1、資料庫升級

原理：建立臨時表-->刪除原表-->建立新表-->複製臨時表資料到新表並刪除臨時表；這樣就實現資料庫表的更新了

新建一個數據庫更新輔助類 MigrationHelper

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);
    }
 
    /**
     * 生成臨時列表
     *
     * @param db
     * @param 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) {
                        exception.printStackTrace();
                    }
                    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());
        }
    }
    /**
     * 儲存新的資料庫表 以及資料
     *
     * @param db
     * @param daoClasses
     */
    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()));
        exception.printStackTrace();
        throw exception;
    }
 
    private 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;
    }
}
 

新建一個MyOpenHelper類：

public class MyOpenHelper extends DaoMaster.OpenHelper {
 
    public MyOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory) {
        super(context, name, factory);
    }
 
    /**
     * 資料庫升級
     * @param db
     * @param oldVersion
     * @param newVersion
     */
    @Override
    public void onUpgrade(Database db, int oldVersion, int newVersion) {
        //操作資料庫的更新 有幾個表升級都可以傳入到下面
 
        Log.i("version", oldVersion + "---先前和更新之後的版本---" + newVersion);
        if (oldVersion < newVersion) {
            Log.i("version", oldVersion + "---先前和更新之後的版本---" + newVersion);
            MigrationHelper.getInstance().migrate(db, BookDao.class);
            //更改過的實體類(新增的不用加)   更新UserDao檔案 可以新增多個  XXDao.class 檔案
//             MigrationHelper.getInstance().migrate(db, UserDao.class,XXDao.class);
        }
        //MigrationHelper.getInstance().migrate(db,StudentDao.class);
    }
}
 

同時DBManager中的getDaoMaster方法要更換成：

/**
     * 獲取DaoMaster
     *
     * 判斷是否存在資料庫，如果沒有則建立資料庫
     * @param context
     * @return
     */
    public static DaoMaster getDaoMaster(Context context) {
        if (null == mDaoMaster) {
            synchronized (DbManager.class) {
                if (null == mDaoMaster) {
                    MyOpenHelper helper = new MyOpenHelper(context,DB_NAME,null);
                    mDaoMaster = new DaoMaster(helper.getWritableDatabase());
                }
            }
        }
        return mDaoMaster;
    }
 

測試一下，在Book類中增加一個屬性publishHouse，將build.gradle裡面schemaVersion改為 2 ，執行後檢視資料庫可以看到增加了新欄位，同時舊資料依然存在。

2、檢測表字段是否存在

private boolean hasColumn(SQLiteDatabase db, String tableName, String column) {
        if (TextUtils.isEmpty(tableName) || TextUtils.isEmpty(column)) {
            return false;
        }
        Cursor cursor = null;
        try {
            cursor = db.query(tableName, null, null, null, null, null, null);
            if (null != cursor && cursor.getColumnIndex(column) != -1) {
                return true;
            }
        } finally {
            if (null != cursor) {
                cursor.close();
            }
        }
        return false;
 }

3、複雜表結構

上一篇在講註解時講到@ToOne和@ToMany ，就是在建立物件時指明表關係的。

（1）@ToOne 建立一對一 ( 1 : 1) 關係

@Entity
public class Order {
    @Id 
    private Long id;
    private long customerId;
    @ToOne(joinProperty = "customerId")
    private Customer customer;
}
@Entity
public class Customer {
    @Id 
    private Long id;
}

（2）@ToMany 建立一對多 (1:N ) 關係

@Entity
public class Customer {
    @Id 
    private Long id;
    @ToMany(referencedJoinProperty = "customerId")
    @OrderBy("date ASC")
    private List<Order> orders;
}
@Entity
public class Order {
    @Id private Long id;
    private Date date;
    private long customerId;
}

（3）@JoinEntity 建立多對多（N : M）關係

@Entity
public class Product {
    @Id private Long id;
    @ToMany
    @JoinEntity(
            entity = JoinProductsWithOrders.class,
            sourceProperty = "productId",
            targetProperty = "orderId"
    )
    private List<Order> ordersWithThisProduct;
}
@Entity
public class JoinProductsWithOrders {
    @Id private Long id;
    private Long productId;
    private Long orderId;
}
@Entity
public class Order {
    @Id private Long id;
}

4、複雜查詢

（1）條件查詢

//方法一：
List<User> userlist = userDao.queryRaw("where AGE>?","10");//查詢年齡大於10的使用者
//方法二：
List<User> userlist = userDao.queryBuilder().where(UserDao.Properties.Age.gt("10")).list();

（2）排序

// order by last name
queryBuilder.orderAsc(Properties.LastName);
// in reverse
queryBuilder.orderDesc(Properties.LastName);
// order by last name and year of birth
queryBuilder.orderAsc(Properties.LastName).orderDesc(Properties.YearOfBirth);

（3）分頁

//limit(int) : 限制查詢返回的結果的數量。 
//offset(int): 設定起始位置
// 從第二條記錄開始查詢5條記錄
List<User> list = userDao.queryBuilder()
                .offset(2)
                .limit(5)
                .list();

（4）懶載入

LazyList<User> lazyList = userDao.queryBuilder().listLazy();
for (User u:lazyList) {
      Log.i(TAG, "使用者名稱："+u.getName());
}
//不再使用時必須關閉，否則會導致資料庫遊標未關閉，從而導致記憶體洩漏
lazyList.close(); 

（5）多表查詢

QueryBuilder<User> queryBuilder = userDao.queryBuilder();
queryBuilder.join(Address.class, AddressDao.Properties.userId)
  .where(AddressDao.Properties.Street.eq("Sesame Street"));
List<User> users = queryBuilder.list();

5、資料庫加密

greenDAO 支援 SQLCipher 直接繫結

引入依賴：

compile 'net.zetetic:android-database-sqlcipher:[email protected]'

初始化資料庫

DevOpenHelper helper = new DevOpenHelper(this, "test.db");
Database db = helper.getEncryptedWritableDb("password");
daoSession = new DaoMaster(db).newSession();

其他操作正常使用