剛開始用的時候知道Gradle里用配置數(shù)據(jù)庫版本的參數(shù)，即：
greendao {
schemaVersion 1
daoPackage 'com.tao.greendao.gen'
targetGenDir 'src/main/java'
}
開始以為升級還不容易么泣特，不就是把schemaVersion 抬高一個版本不就ok了嗎。但有實際需求的時候就不是這么回事了宅粥。
把schemaVersion 變成2的時候帮碰，一運行，再查看數(shù)據(jù)庫尼酿。要加的字段確實添加進來了爷狈。但是以前保存的數(shù)據(jù)都沒有了。這樣在保留數(shù)據(jù)升級的場景中就不適用了裳擎。我們要想不刪除涎永，首先要了解下GreenDao是怎么做的，那就從代碼入手吧鹿响。
DaoMaster中的代碼：
/** 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);
}
}
人家早就說啦Use only during development.羡微，都怪自己沒看代碼。代碼中寫的很明確惶我，升級的時候是刪除所有表妈倔，然后再重新創(chuàng)建數(shù)據(jù)庫。
我們應(yīng)該每次提高數(shù)據(jù)庫版本的時候在表中插入新的字段不就行了嗎绸贡，于是出現(xiàn)了如下代碼：
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
if (oldVersion < 2) {
db.execSQL(String.format("ALTER TABLE %s ADD %s varchar", 表名, 字段名))启涯；
}
if (oldVersion < 3) {
db.execSQL(String.format("ALTER TABLE %s ADD %s integer default 0", 表名,字段名));
}
}
項目上線后，隨著數(shù)據(jù)庫的不斷升級恃轩，onUpgrade中的代碼越來越多。時間久了會吐了的黎做。所以要換一種寫法叉跛，大體思路：
1.首先創(chuàng)建臨時表。
2.把當前表的數(shù)據(jù)插入到臨時表中去蒸殿。
3.刪除掉原表筷厘，創(chuàng)建新表。
4.把臨時表數(shù)據(jù)插入到新表中去宏所，然后刪除臨時表酥艳。
感覺還是很復(fù)雜，就在網(wǎng)上找了下爬骤，有人已經(jīng)寫好了：
/**
* 作者：WangJintao
* 時間：2017/4/17
* 郵箱：wangjintao1988@163.com
*/
public class MySqlLiteOpenHelper extends DaoMaster.DevOpenHelper {
public MySqlLiteOpenHelper(Context context, String name) {
super(context, name);
}
public MySqlLiteOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory) {
super(context, name, factory);
}
@Override
public void onUpgrade(Database db, int oldVersion, int newVersion) {
MigrationHelper.getInstance().migrate(db, StudentDao.class);
}
}
/**
* 作者：WangJintao
* 時間：2017/4/17
* 郵箱：wangjintao1988@163.com
*/
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", "創(chuàng)建臨時表的SQL語句： " + 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", "在臨時表插入數(shù)據(jù)的SQL語句：" + 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語句：" + insertTableStringBuilder.toString());
Log.i("lxq", "銷毀臨時表的SQL語句：" + 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;
}
}
MigrationHelper.getInstance().migrate(db, StudentDao.class);
中可以把所有的XXXDao.class都傳進去充石。
修改后的DaoManager變成這樣：
/**
* 作者：WangJintao
* 時間：2017/4/17
* 郵箱：wangjintao1988@163.com
*/
public class GreenDaoManager {
private static DaoMaster mDaoMaster;
private static DaoSession mDaoSession;
private static volatile GreenDaoManager mInstance = null;
private static final String DB_NAME = "GreenDao.db";
private GreenDaoManager() {
}
public static void init(Context context) {
MySqlLiteOpenHelper devOpenHelper = new
MySqlLiteOpenHelper(context, DB_NAME);
mDaoMaster = new DaoMaster(devOpenHelper.getWritableDatabase());
mDaoSession = mDaoMaster.newSession();
}
public static GreenDaoManager getInstance() {
if (mInstance == null) {
synchronized (GreenDaoManager.class) {
if (mInstance == null) {
mInstance = new GreenDaoManager();
}
}
}
return mInstance;
}
public DaoSession getSession() {
return mDaoSession;
}
}
在Application中初始化：
GreenDaoManager.init(this);
還有個問題沒搞出來，希望哪位會的指點一下
某個Entity中有個字段是List<String>該怎么存儲呢
