GreenDao数据库升级方案

GrenDao的深入使用

在本文中将会讲解一些使用GreenDao的FAQ（Frequently Asked Questions经常遇到的问题）

混淆

### greenDAO 3
-keepclassmembers class * extends org.greenrobot.greendao.AbstractDao {
public static java.lang.String TABLENAME;
}
-keep class **$Properties

# If you do not use SQLCipher:
-dontwarn org.greenrobot.greendao.database.**
# If you do not use RxJava:
-dontwarn rx.**

### greenDAO 2
-keepclassmembers class * extends de.greenrobot.dao.AbstractDao {
public static java.lang.String TABLENAME;
}
-keep class **$Properties

GreenDao修改生成目录

//目录设置
sourceSets {
main {
java.srcDirs = ['src/main/java', 'src/main/greendao']
jniLibs.srcDirs=['./libs']
}
}
//GreenDao设置
greendao{
targetGenDir 'src/main/greendao'
daoPackage 'com.greendao'
schemaVersion 1
}

数据库升级

先看DaoMaster生成的代码。

/** WARNING: Drops all table on Upgrade! Use only during development. */
public static class DevOpenHelper extends OpenHelper {
public DevOpenHelper(Context context, String name) {
super(context, name);
}

public DevOpenHelper(Context context, String name, CursorFactory factory) {
super(context, name, factory);
}

@Override
public void onUpgrade(Database db, int oldVersion, int newVersion) {
Log.i("greenDAO", "Upgrading schema from version " + oldVersion + " to " + newVersion + " by dropping all tables");
dropAllTables(db, true);
onCreate(db);
}
}

2、如果自定义的SqliteOpenHelper是继承自DevOpenHelper，那么在升级数据的时候会把所有表删除掉，然后创建新的表。

这种方式进行升级数据库，会照成原始数据的缺失，所以实际情况中是不运行出现这种升级方式的，这种方式使用于测试期，也就是版本未上线期间。

那么如果我们要进行数据库的保留数据升级，我们应该怎么做呢?

1.首先我们需要重写onUpgrade方法，那么先自定义SqliteOpenHeler

public class MySqlLiteOpenHelper extends DaoMaster.OpenHelper{

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

@Override
public void onUpgrade(Database db, int oldVersion, int newVersion) {
Log.i("greendao","oldVersion:"+oldVersion+",newVersion"+newVersion);
switch (oldVersion){
case 1:
db.execSQL("SQL语句");
break;
case 2:
db.execSQL("SQL语句");
break;
case 3:
db.execSQL("SQL语句");
break;
…………
}
}

}

2.以前确实是这么写的，数据库的升级也的确是这么搞的，但是当项目上线以后，数据库庞大，迭代版本次数多，每一次迭代，都需要升级数据库，Swith语句越来越庞大。我们该怎么办呢？

3.先提供思路给大家参考（PS：不是标准答案）。

（1）首先创建临时表（数据格式和原表一模一样）。

（2）把当前表的数据插入到临时表中去。

（3）删除掉原表，创建新表。

（4）把临时表数据插入到新表中去，然后删除临时表。

在这样基础上，可以保留原数据进行升级数据库。

4.本着拿来主义，因为国外大牛已经有对这些进行封装，所以直接把代码贴出来了

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;
}

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;
}

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(");");
Log.i("lxq", "创建临时表的SQL语句： " + createTableStringBuilder.toString());
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(";");
Log.i("lxq", "在临时表插入数据的SQL语句：" + insertTableStringBuilder.toString());
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();
ArrayList<String> propertiesQuery = 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);
propertiesQuery.add(columnName);
} else {
try {
if (getTypeByClass(daoConfig.properties[j].type).equals("INTEGER")) {
propertiesQuery.add("0 as " + columnName);
properties.add(columnName);
}
} catch (Exception e) {
e.printStackTrace();
}
}
}

StringBuilder insertTableStringBuilder = new StringBuilder();

insertTableStringBuilder.append("INSERT INTO ").append(tableName).append(" (");
insertTableStringBuilder.append(TextUtils.join(",", properties));
insertTableStringBuilder.append(") SELECT ");
insertTableStringBuilder.append(TextUtils.join(",", propertiesQuery));
insertTableStringBuilder.append(" FROM ").append(tempTableName).append(";");

StringBuilder dropTableStringBuilder = new StringBuilder();

dropTableStringBuilder.append("DROP TABLE ").append(tempTableName);
Log.i("lxq", "插入正式表的SQL语句：" + insertTableStringBuilder.toString());
Log.i("lxq", "销毁临时表的SQL语句：" + dropTableStringBuilder.toString());
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) || type.equals(int.class)) {
return "INTEGER";
}
if (type.equals(Boolean.class) || type.equals(boolean.class)) {
return "BOOLEAN";
}

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

5.使用以上工具类的时候，onUpgrade方法就变成以下这么简单了。

public class MySqlLiteOpenHelper extends DaoMaster.OpenHelper{

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

@Override
public void onUpgrade(Database db, int oldVersion, int newVersion) {
Log.i("lxq","oldVersion:"+oldVersion+",newVersion"+newVersion);
MigrationHelper.getInstance().migrate(db,UserDao.class);
}

}

6.使用注意：要把为了不忘记某些XXDao.class,最好把所有的XXDao.class丢进去。

GreenDao的封装

public class DaoManager {
private static String DB_NAME = "test.db";
private static DaoManager mDaoManager;
private static MySqlLiteOpenHelper mySqlLiteOpenHelper;
private static DaoSession mDaoSession;
private static Database mDatabase;
private DaoManager() {}

public static DaoManager getInstance(){
if (mDaoManager == null){
synchronized (DaoManager.class){
if (mDaoManager == null){
mDaoManager = new DaoManager();
}
}
}
return mDaoManager;
}

public static void init(Context context){
mySqlLiteOpenHelper = new MySqlLiteOpenHelper(context,DB_NAME,null);
mDatabase = mySqlLiteOpenHelper.getWritableDb();
mDaoSession = new DaoMaster(mDatabase).newSession();
}

public DaoSession getDaoSession(){
return mDaoSession;
}
}

这个管理类中，我把DaoSession给暴漏出来，然后可以通过DaoSession获取XXDao，然后进行操作数据库。下面可以看我的例子：

public class UserDaoManagr implements IDao<User> {
private DaoSession mDaoSession = DaoManager.getInstance().getDaoSession();

@Override
public boolean insert(User user) {
return mDaoSession.getUserDao()
.insert(user) > 0 ? true : false;
}

@Override
public boolean delete(User user) {
try {
mDaoSession.getUserDao()
.delete(user);
} catch (Exception e) {
Log.e("lxq", "删除失败");
return false;
}
return true;
}

@Override
public boolean update(User user) {
try {
mDaoSession.getUserDao()
.update(user);
} catch (Exception e) {
Log.e("lxq", "更新失败");
return false;
}
return true;
}

@Override
public List<User> queryAll() {
return mDaoSession.getUserDao()
.loadAll();
}

@Override
public User queryById(long id) {
return mDaoSession.getUserDao()
.loadByRowId(id);
}

@Override
public List<User> queryByObj(String where, String... params) {
return mDaoSession.getUserDao()
.queryRaw(where, params);
}

public User queryByName(String name) {
return mDaoSession.getUserDao()
.queryBuilder()
.where(UserDao.Properties.Name.eq(name))
.build()
.unique();
}
}

要想使用DaoManager，别忘记在Application中初始化。

DaoManager.init(this);