GreenDAO是一款非要流行的android平台上的數據庫框架，性能優秀，代碼簡潔。
初始化數據庫模型代碼的時候需要使用java項目生成代碼，依賴的jar包已經上傳到我的資源里了，下載地址如下：http://download.csdn.net/detail/fancylovejava/8859203
項目開發中用到的就是GreenDAO數據庫框架，需要進行數據庫版本升級。
其實數據庫版本升級比較麻煩的就是數據的遷移，data migration。
數據庫版本升級有很多方法，按不同需求來處理。
本質上是去執行sql語句去創建臨時數據表，然后遷移數據，修改臨時表名等。
數據版本升級，為了便於維護代碼可以先定義一個抽象類
public abstract class AbstractMigratorHelper { public abstract void onUpgrade(SQLiteDatabase db); }
然后讓自己更新數據庫邏輯的類繼承這個類
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方法里面處理，這里方法調用的比較巧妙，借用國外大牛的代碼復制下。
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; } } } }
上面已經做了數據的遷移，國外有個大牛封裝的代碼摘抄下來：
/**
* 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方法里面去調用
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); }
上面代碼全是干貨，記錄下來以備不時之需！