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介紹

GreenDAO是一個對象關系映射(ORM)的框架，能夠提供相關接口，通過操作對象的方式去操作關系型數據庫。GreenDao官網介紹: greenDAO is a light & fast ORM solution for Android that maps objects to SQLite databases.

greenDao作為java對象和SQLite數據庫之間的橋梁

GreenDao的優勢

greenDao與OrmLite、ActiveAndroid對比

輕量級
增刪改查操作快速
內存開銷小，性能好
Api接口完善，方便初學者使用

GreenDao2.0配置

在gradle中引入：

compile 'de.greenrobot:greendao:2.0.0'

GreenDao2.0使用

創建本地數據庫及表
新建一java工程，導入greendao-generator-1.3.1.jar到libs中，main文件中寫：
public class ExampleDaoGenerator {
public static void main(String[] args) throws Exception {
//第一個參數是數據庫版本號，第二個參數是包名
Schema schema = new Schema(version, "你的包名路徑");
//給數據庫新增一張表
addMessage(schema);
//第二個參數是文件生成路徑
new DaoGenerator().generateAll(schema, LocalConstants.CODE_PATH);
}
private static void addMessage(Schema schema) {
//表實體，會對應生成一張表
Entity note = schema.addEntity("MessageEntity");
//給表添加一個主鍵
note.addStringProperty("msgId").primaryKey().notNull();
//boolean類型字段，對應列名
note.addBooleanProperty("isRead");
//字符類型字段，對應列名
note.addStringProperty("createTime");
}
}
執行Main()方法，數據庫映射文件將會在LocalConstants.CODE_PATH路徑下生成。

數據庫的使用（表的增刪改查）
public class DbHelper {
private final static String DB_NAME = "xxx.db";
private static volatile DbHelper dbHelper;
private DaoSession daoSession;
private DaoMaster daoMaster;
private MessageEntityDao messageEntityDao;
public static DbHelper getInstance() {
if (null == dbHelper) {
synchronized (DbHelper.class) {
if (null == dbHelper) {
dbHelper = new DbHelper();
dbHelper.daoSession = dbHelper.getDaoSession(XxxApplication.getInstance());
dbHelper.messageEntityDao = dbHelper.daoSession.getMessageEntityDao();
}
}
}
return dbHelper;
}
private DbHelper() {

    }

  private DaoSession getDaoSession(Context context) {
    if (daoSession == null) {
      if (daoMaster == null) {
          daoMaster = getDaoMaster(context);
      }
      daoSession = daoMaster.newSession();
    }
    return daoSession;
  }
  private DaoMaster getDaoMaster(Context context) {
  if (daoMaster == null) {
      DaoMaster.OpenHelper helper = new DaoMaster.DevOpenHelper(context, DB_NAME, null);
      daoMaster = new DaoMaster(helper.getWritableDatabase());
  }
  return daoMaster;
}
//保存一條消息
public long saveMessageEntity(MessageEntity messageEntity) {
  if (null == messageEntity) {
      return -1;
  }
  long result = -1;
  try {
      result = messageEntityDao.insertOrReplace(messageEntity);
  } catch (ClassCastException ex) {
      MLog.e("ClassCastException", "ClassCastException");
  } catch (Exception ex) {
      ex.printStackTrace();
  }
  return result;
}
//查詢未讀消息數
public int getNoReadMsg() {
  try {
      return messageEntityDao.queryBuilder().where(MessageEntityDao.Properties.IsRead.eq(false)).build().list().size();
  } catch (Exception e) {
      e.printStackTrace();
      return 0;
  }
}
//查消息類型對應的未讀消息條數
public int getNoReadMsgCountByMsgType(String msgType) {
  try {
      return messageEntityDao.queryBuilder().where( MessageEntityDao.Properties.MsgType.eq(msgType), MessageEntityDao.Properties.IsRead.eq(false)).build().list().size();
  } catch (Exception e) {
      e.printStackTrace();
      return 0;
  }
}
//查詢消息
public MessageEntity getMsgByMsgId(String msgId) {
    try {
      return messageEntityDao.queryBuilder().where(MessageEntityDao.Properties.MsgId.eq(msgId)).build().unique();
      } catch (Exception e) {
      e.printStackTrace();
      return null;
      }
  }
}

說明：
使用DevOpenHelper打開數據庫
DaoMaster.DevOpenHelper helper = new DevOpenHelper(context,"xxx.db",null);
我們查看下DevOpenHelper內容
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);
  }
  }

可以發現，當數據庫版本更新時，會執行onUpgrade方法，先刪除原有的數據表，再新建表。

數據庫升級

當我們的app版本升級時，當對本地數據庫表結構修改時，就有必要對本地數據庫升級。我們只需要修改下DaoMaster文件中的SCHEMA_VERSION常量(增1)，它就會執行onUpgrade()。
public class DaoMaster extends AbstractDaoMaster {
public static final int SCHEMA_VERSION = 128;
public static void createAllTables(SQLiteDatabase db, boolean ifNotExists) {
MessageEntityDao.createTable(db, ifNotExists);
}
......
}
有時我們并不想把原有的表數據也刪除，那要怎么做呢？
其核心思路是

把舊表改為臨時表
建立新表
臨時表數據寫入新表，刪除臨時表

代碼實現：
/**
*表字段有改變的時候需要用到合并數據
*Created by wangfengkai on 17/3/11.
*Github:https://github.com/github/jxwangfengkai
*/
public class DbOpenHelper extends DaoMaster.OpenHelper {
public DbOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory) {
super(context, name, factory);
}

    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
      //操作數據庫的更新
      MigrationHelper.getInstance().migrate(sqLiteDatabase, MessageEntityDao.class);
    }
  }

  /**
   * MigrationHelper類
   */
  public class MigrationHelper {
      private static final String CONVERSION_CLASS_NOT_FOUND_EXCEPTION = "MIGRATION HELPER - CLASS DOESN'T MATCH WITH THE CURRENT PARAMETERS";
      private static final String TAG = "MigrationHelper";
      private static volatile 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) {
                          Log.e(TAG, "CrashType:" + daoConfig.properties[j].type);
                          exception.printStackTrace();
                      }
                      createTableStringBuilder.append(divider).append(columnName).append(" ").append(type);

                      if (daoConfig.properties[j].primaryKey) {
                          createTableStringBuilder.append(" PRIMARY KEY");
                      }

                      divider = ",";
                  }
              }
              createTableStringBuilder.append(");");
              String createSql = createTableStringBuilder.toString();
              if (!createSql.contains("();")) {
                  //說明沒有表
                  db.execSQL(createSql);
                  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(";");

                  String insertTableSql = insertTableStringBuilder.toString();
                  Log.e(TAG, daoConfig.tablename + "__insertTableSql:" + insertTableSql);
                  db.execSQL(insertTableSql);
              }
          }
      }

      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 IF EXISTS ").append(tempTableName);

              String insertSQL = insertTableStringBuilder.toString();
              if (properties.size() > 0) {
                  Log.e(TAG, daoConfig.tablename + "__restoreData__insertSQL:" + insertSQL);
                  db.execSQL(insertSQL);
              }
              String dropTableSql = dropTableStringBuilder.toString();
              Log.e(TAG, daoConfig.tablename + "__restoreData__dropTableSql:" + dropTableSql);
              db.execSQL(dropTableSql);
          }
      }

      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) || type.equals(int.class) || type.equals(Boolean.class) || type.equals(boolean.class)) {
              return "INTEGER";
          }

          Exception exception = new Exception(CONVERSION_CLASS_NOT_FOUND_EXCEPTION.concat(" - Class: ").concat(type.toString()));
          exception.printStackTrace();
          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;
      }
  }

所以，當需要數據庫升級時，我們使用
DbOpenHelper helper = new DbOpenHelper(context,"xxx.db",null);
來打開數據庫。
講到這里，GreenDao2.0的使用基本已經完了，下一篇，我將為大家講解GreenDao3.0的優化及使用。
喜歡就點個贊哦。

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GreenDao2.0使用詳解

GreenDao2.0使用詳解

介紹

GreenDao的優勢

GreenDao2.0配置

GreenDao2.0使用

數據庫升級

推薦閱讀更多精彩內容

三个男躁一个女,国精产品一区一手机的秘密,麦子交换系列最经典十句话,欧美 国产 综合 欧美 视频

GreenDao2.0使用詳解

介紹

GreenDao的優勢

GreenDao2.0配置

GreenDao2.0使用

數據庫升級

推薦閱讀更多精彩內容

三个男躁一个女,国精产品一区一手机的秘密,麦子交换系列最经典十句话,欧美国产综合欧美视频