GreenDao数据库的升级
应用使用了GreenDao数据库,在版本升级的时候需要更改dao的字段,新增、修改、删除字段操作,如果直接删除原来的表的话那用户原来的一些数据就没有了,所以在更新数据库的时候需要做一次封装,把原来的数据保存后再更新数据库版本;
代码是用的网上的大神的,经过一些修改。利用这个类替换在Application里面的Helper类就可以完成数据的迁移了。
import android.database.Cursor; import android.text.TextUtils; import android.util.Log; import com.example.bob.testlistener.database.greendao.DaoMaster; import org.greenrobot.greendao.AbstractDao; import org.greenrobot.greendao.database.Database; import org.greenrobot.greendao.internal.DaoConfig; import java.util.ArrayList; import java.util.Arrays; import java.util.List; /** * Created by pokawa on 18/05/15. * 数据迁移类(数据库版本升级的时候使用这个类,会保留先前版本的数据) */ 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); } 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()); } } 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())); // Crashlytics.logException(exception); throw exception; } private static 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; } }
这是在application里面的初始化GreenDao方法
/** * 初始化GreenDao */ private void initGreenDao() { MyGreenHelper helper = new MyGreenHelper(this,"test_user.db"); SQLiteDatabase db = helper.getWritableDatabase(); DaoMaster daoMaster = new DaoMaster(db); daoSession = daoMaster.newSession(); }
完成上面的修改后,就能够在entity里面更改数据库的字段了,然后make一下工程,生成新的daoMaster;
最后在gradle文件里面更改数据库版本号
greendao { schemaVersion 2 //数据库版本号 daoPackage 'com.example.bob.testlistener.database.greendao'// 设置DaoMaster、DaoSession、Dao 包名 targetGenDir 'src/main/java'//设置DaoMaster、DaoSession、Dao目录 }
数据库更新后原来的数据的新增或者更改字段的值都是null,需要在代码里面做相应的处理。