记录一下寄几个儿的greendao数据库升级，可以说是非常菜鸡了嗯

之前使用的greendao数据库存储服务器所有的历史推送消息，但是后来消息需要加几个新的字段举个栗子，比如要新增红色框住的字段到数据库中：

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);
}

/**
* 生成临时列表
*
* @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());

}
}

/**
* 存储新的数据库表 以及数据
*
* @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;
}
}

MigrationHelper

public class MyOpenHelper extends DaoMaster.OpenHelper {
public MyOpenHelper(Context context, String name) {
super(context, name);
}

public MyOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory) {
super(context, name, factory);
}

/**
* 数据库升级
*/
@Override
public void onUpgrade(Database db, int oldVersion, int newVersion) {
//操作数据库的更新 有几个表升级都可以传入到下面
MigrationHelper.getInstance().migrate(db, MyBeanDao.class);
}
}

public class DbManager {

// 是否加密
public static final boolean ENCRYPTED = true;

private static final String DB_NAME = "petssions.db";
private static DbManager mDbManager;
private static DaoMaster.DevOpenHelper mDevOpenHelper;
private static DaoMaster mDaoMaster;
private static DaoSession mDaoSession;

private Context mContext;

public DbManager(Context context) {
this.mContext = context;
// 初始化数据库信息
mDevOpenHelper = new DaoMaster.DevOpenHelper(context, DB_NAME);
getDaoMaster(context);
getDaoSession(context);
}

public static DbManager getInstance(Context context) {
if (null == mDbManager) {
synchronized (DbManager.class) {
if (null == mDbManager) {
mDbManager = new DbManager(context);
}
}
}
return mDbManager;
}

/**
* 获取可读数据库
*
* @param context
* @return
*/
public static SQLiteDatabase getReadableDatabase(Context context) {
if (null == mDevOpenHelper) {
getInstance(context);
}
return mDevOpenHelper.getReadableDatabase();
}

/**
* 获取可写数据库
*
* @param context
* @return
*/
public static SQLiteDatabase getWritableDatabase(Context context) {
if (null == mDevOpenHelper) {
getInstance(context);
}
return mDevOpenHelper.getWritableDatabase();
}

/**
* 获取DaoMaster
*
* 判断是否存在数据库，如果没有则创建数据库
* @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;
}

/**
* 获取DaoSession
*
* @param context
* @return
*/
public static DaoSession getDaoSession(Context context) {
if (null == mDaoSession) {
synchronized (DbManager.class) {
mDaoSession = getDaoMaster(context).newSession();
}
}

return mDaoSession;
}

④.可以直接用DBManager里的方法获取dao类了，比如

DbManager.getDaoSession(getApplicationContext()).getBeanDao();

且原数据库中数据依旧保留。

详细代码取自 https://blog.csdn.net/huangxiaoguo1/article/details/54574713