問(wèn)題描述
前段時(shí)間在公司有項(xiàng)目需要更新版本吠卷。在新增的功能需求里王悍，需要對(duì)greendao里的Entity實(shí)體類(lèi)新增一個(gè)字段当船。
最開(kāi)始覺(jué)得只需要新增一個(gè)對(duì)象后题画，在gradle中修改greendao版本號(hào)之后重新build項(xiàng)目即可。
@Entity
public class BibleInspirationDB implements Serializable {
static final long serialVersionUID = -15515456L;
@Id(autoincrement = true)
private Long _id;
private String bibleId; //書(shū)籍ID
private String bookName; //書(shū)名
private String InspirationContent; //靈感的文本
private String rollTitle;
private String rollIndex; //第幾卷
private String secIndex; //第幾章
private String partIndex; //第幾節(jié) 節(jié)可以保存多個(gè)德频，用,隔開(kāi)
private long saveTime;
private String content;
private String netId;
private String testId; //---->需要新增的字段
@Transient //：添加此標(biāo)記后不會(huì)生成數(shù)據(jù)庫(kù)表的列
private boolean isSelected;
......
升級(jí)greendao版本
greendao {
//指定數(shù)據(jù)庫(kù)schema版本號(hào)苍息，遷移等操作會(huì)用到
schemaVersion 16 // 將上一版本的15修改為16
}
但是在重新運(yùn)行項(xiàng)目后報(bào)錯(cuò)提示沒(méi)有辦法找到新增字段。
原因：
后進(jìn)過(guò)多次排查 發(fā)現(xiàn)是在配置greendao版本的時(shí)候，將其寫(xiě)在了
android{
....
greendao {
//指定數(shù)據(jù)庫(kù)schema版本號(hào)竞思，遷移等操作會(huì)用到
schemaVersion 16 // 將上一版本的15修改為16
}
}
導(dǎo)致更改版本號(hào)之后無(wú)法識(shí)別
補(bǔ)充：
當(dāng)發(fā)現(xiàn)一些有違正潮硪辏現(xiàn)象的問(wèn)題時(shí)，且在網(wǎng)上無(wú)法相同現(xiàn)象的情況盖喷，大多數(shù)原因是因?yàn)殚_(kāi)發(fā)過(guò)程中一些基礎(chǔ)的配置出現(xiàn)問(wèn)題引起爆办。當(dāng)往往因?yàn)榻?jīng)常配置該設(shè)置，所以出現(xiàn)問(wèn)題的同時(shí)不會(huì)意識(shí)到是最初的原因引起的课梳。這一點(diǎn)望自己在今后開(kāi)發(fā)過(guò)程中牢記距辆。
此次學(xué)習(xí)到的一些額外知識(shí)
這次在網(wǎng)上尋找問(wèn)題時(shí)，發(fā)現(xiàn)有其他博主提到暮刃，在greendao新增字段更新后挑格，會(huì)出現(xiàn)原有的舊數(shù)據(jù)被清除的情況。他們的建議方案是在初始化數(shù)據(jù)庫(kù)時(shí)沾歪，將舊表數(shù)據(jù)copy到新表中，然后刪除舊表雾消。
國(guó)外有人開(kāi)源實(shí)現(xiàn)類(lèi)灾搏，親測(cè)可用
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(shí)表的SQL語(yǔ)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(shí)表插入數(shù)據(jù)的SQL語(yǔ)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(yǔ)句：" + insertTableStringBuilder.toString());
Log.i("lxq", "銷(xiāo)毀臨時(shí)表的SQL語(yǔ)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;
}
}
然后自己寫(xiě)一個(gè)Helper類(lèi)，重寫(xiě)onUpgrade方法立润，在里邊實(shí)現(xiàn)數(shù)據(jù)庫(kù)的數(shù)據(jù)備份
public class MySqlLiteOpenHelper extends DaoMaster.OpenHelper{
public MySqlLiteOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory) {
super(context, name);
}
@Override
public void onCreate(Database db) {
super.onCreate(db);
/**
* 這個(gè)方法
* 1狂窑、在第一次打開(kāi)數(shù)據(jù)庫(kù)的時(shí)候才會(huì)走
* 2、在清除數(shù)據(jù)之后再次運(yùn)行-->打開(kāi)數(shù)據(jù)庫(kù)桑腮，這個(gè)方法會(huì)走
* 3泉哈、沒(méi)有清除數(shù)據(jù)，不會(huì)走這個(gè)方法
* 4破讨、數(shù)據(jù)庫(kù)升級(jí)的時(shí)候這個(gè)方法不會(huì)走
*/
}
@Override
public void onUpgrade(Database db, int oldVersion, int newVersion) {
super.onUpgrade(db, oldVersion, newVersion);
/**
* 1丛晦、第一次創(chuàng)建數(shù)據(jù)庫(kù)的時(shí)候，這個(gè)方法不會(huì)走
* 2提陶、清除數(shù)據(jù)后再次運(yùn)行(相當(dāng)于第一次創(chuàng)建)這個(gè)方法不會(huì)走
* 3烫沙、數(shù)據(jù)庫(kù)已經(jīng)存在，而且版本升高的時(shí)候隙笆，這個(gè)方法才會(huì)調(diào)用
*/
if (oldVersion < newVersion) {
MigrationHelper.getInstance().migrate(db, BibleLineAtionDBDao.class);
MigrationHelper.getInstance().migrate(db, BibleInspirationDBDao.class);
}
}
@Override
public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
super.onDowngrade(db, oldVersion, newVersion);
/**
* 執(zhí)行數(shù)據(jù)庫(kù)的降級(jí)操作
* 1锌蓄、只有新版本比舊版本低的時(shí)候才會(huì)執(zhí)行
* 2、如果不執(zhí)行降級(jí)操作撑柔，會(huì)拋出異常
*/
}
}
初始化Greendao
public class DBRepository {
public static final String DB_NAME = "data-db";//數(shù)據(jù)庫(kù)名稱(chēng)
private static DaoSession mDaoSession;
private static MySqlLiteOpenHelper mySqlLiteOpenHelper;
/**
* 初始化greenDao瘸爽，這個(gè)操作建議在Application初始化的時(shí)候添加；
*/
public static void initDatabase(Context context) {
if (context == null) {
throw new IllegalArgumentException("You cannot start a load on a null Context");
}
// DatabaseOpenHelper mHelper = new DaoMaster.DevOpenHelper(context.getApplicationContext(), DB_NAME);
// Database db = mHelper.getWritableDb();
mySqlLiteOpenHelper = new MySqlLiteOpenHelper(context.getApplicationContext(),DB_NAME,null);
Database db = mySqlLiteOpenHelper.getWritableDb();
DaoMaster mDaoMaster = new DaoMaster(db);
mDaoSession = mDaoMaster.newSession();
}
public static DaoSession getDaoSession() {
return mDaoSession;
}
}
在Application中實(shí)現(xiàn)初始化
private void initDataBase() {
DBRepository.initDatabase(MyApplication.getContext());
}
