一、GreenDao 集成、基本使用
greenDAO是一款開源的面向 Android 的輕便、快捷的 ORM 框架,將 Java 對象映射到 SQLite 數據庫中,我們操作數據庫的時候,無需要編寫複雜的 SQL語句, 在性能方面,greenDAO 針對 Android 進行了高度優化, 最小的內存開銷 、依賴體積小 同時還是支持數據庫加密。
下面連接是集成和使用的詳細說明:GreenDao集成和使用
二、GreenDAO的數據庫升級說明
如下圖所示我的工程有 Animal、Book、People,即有三張表。
另外還有DAOMaster、DAOSession。DAOMaster主要是負責數據庫創建和升級,DAOSession負責獲得實體類的xxxDAO,來進行增刪改查。
DAOMaster內部有個OpenHelper,繼承DatabaseOpenHelper,DatabaseOpenHelper又繼承SQLiteOpenHelper。
(另外,DAOMaster內部還有個DevOpenHelper,在升級數據庫的時候會把所有表刪除掉,然後創建新的表,會會照成原始數據的缺失。)
/**
* Calls {@link #createAllTables(Database, boolean)} in {@link #onCreate(Database)} -
*/
public static abstract class OpenHelper extends DatabaseOpenHelper {
public OpenHelper(Context context, String name) {
super(context, name, SCHEMA_VERSION);
}
public OpenHelper(Context context, String name, CursorFactory factory) {
super(context, name, factory, SCHEMA_VERSION);
}
@Override
public void onCreate(Database db) {
Log.i("greenDAO", "Creating tables for schema version " + SCHEMA_VERSION);
createAllTables(db, false);
}
}
可以看到,OpenHelper就是SQLiteOpenHelper的封裝,且是抽象類,所以重點來了:
數據庫升級 需要我們自行處理,即繼承OnUpgrade()。那這樣就和以往SQLiteOpenHelper一樣,需要判斷版本號,然後寫SQL進行新增字段或新增表。這樣顯然不好,我們就是不想寫SQL的,而且版本號判斷維護麻煩。
所以怎麼辦?有辦法:
1.在根目錄的build.gradle文件的repositories內添加如下代碼:
allprojects {
repositories {
...
maven { url "https://jitpack.io" }
}
}
2.添加依賴
dependencies {
compile 'com.github.yuweiguocn:GreenDaoUpgradeHelper:v0.0.5'
}
3、繼承DaoMaster.OpenHelper,自定義OnUpgrade()。
public class MySqlLiteOpenHelper extends DaoMaster.OpenHelper {
public MySqlLiteOpenHelper(Context context, String name) {
super(context, name);
}
@Override
public void onUpgrade(Database db, int oldVersion, int newVersion) {
MigrationHelper.migrate(db, PeopleDao.class, AnimalDao.class, BookDao.class);
}
}
重點是紅色的一行,沒錯就是一行!搞定。
這一行代碼的實現原理,實際就是以下思路。 在此基礎上,可以保留原數據進行升級數據庫。
(1)首先創建臨時表(數據格式和原表一模一樣)。
(2)把當前表的數據插入到臨時表中去。
(3)刪除掉原表,創建新表。
(4)把臨時表數據插入到新表中去,然後刪除臨時表。
因爲大牛已經對這些進行封裝,所以直接把MigrationHelper代碼貼出來。
不難看出,migrate()方法按照以上思路完成的。
public final class MigrationHelper {
public static boolean DEBUG = false;
private static String TAG = "MigrationHelper";
private static final String SQLITE_MASTER = "sqlite_master";
private static final String SQLITE_TEMP_MASTER = "sqlite_temp_master";
private static WeakReference<ReCreateAllTableListener> weakListener;
public interface ReCreateAllTableListener{
void onCreateAllTables(Database db, boolean ifNotExists);
void onDropAllTables(Database db, boolean ifExists);
}
public static void migrate(SQLiteDatabase db, Class<? extends AbstractDao<?, ?>>... daoClasses) {
printLog("【The Old Database Version】" + db.getVersion());
Database database = new StandardDatabase(db);
migrate(database, daoClasses);
}
public static void migrate(SQLiteDatabase db, ReCreateAllTableListener listener, Class<? extends AbstractDao<?, ?>>... daoClasses) {
weakListener = new WeakReference<>(listener);
migrate(db, daoClasses);
}
public static void migrate(Database database, ReCreateAllTableListener listener, Class<? extends AbstractDao<?, ?>>... daoClasses) {
weakListener = new WeakReference<>(listener);
migrate(database, daoClasses);
}
public static void migrate(Database database, Class<? extends AbstractDao<?, ?>>... daoClasses) {
printLog("【Generate temp table】start");
generateTempTables(database, daoClasses);
printLog("【Generate temp table】complete");
ReCreateAllTableListener listener = null;
if (weakListener != null) {
listener = weakListener.get();
}
if (listener != null) {
listener.onDropAllTables(database, true);
printLog("【Drop all table by listener】");
listener.onCreateAllTables(database, false);
printLog("【Create all table by listener】");
} else {
dropAllTables(database, true, daoClasses);
createAllTables(database, false, daoClasses);
}
printLog("【Restore data】start");
restoreData(database, daoClasses);
printLog("【Restore data】complete");
}
private static void generateTempTables(Database db, Class<? extends AbstractDao<?, ?>>... daoClasses) {
for (int i = 0; i < daoClasses.length; i++) {
String tempTableName = null;
DaoConfig daoConfig = new DaoConfig(db, daoClasses[i]);
String tableName = daoConfig.tablename;
if (!isTableExists(db, false, tableName)) {
printLog("【New Table】" + tableName);
continue;
}
try {
tempTableName = daoConfig.tablename.concat("_TEMP");
StringBuilder dropTableStringBuilder = new StringBuilder();
dropTableStringBuilder.append("DROP TABLE IF EXISTS ").append(tempTableName).append(";");
db.execSQL(dropTableStringBuilder.toString());
StringBuilder insertTableStringBuilder = new StringBuilder();
insertTableStringBuilder.append("CREATE TEMPORARY TABLE ").append(tempTableName);
insertTableStringBuilder.append(" AS SELECT * FROM ").append(tableName).append(";");
db.execSQL(insertTableStringBuilder.toString());
printLog("【Table】" + tableName +"\n ---Columns-->"+getColumnsStr(daoConfig));
printLog("【Generate temp table】" + tempTableName);
} catch (SQLException e) {
Log.e(TAG, "【Failed to generate temp table】" + tempTableName, e);
}
}
}
private static boolean isTableExists(Database db, boolean isTemp, String tableName) {
if (db == null || TextUtils.isEmpty(tableName)) {
return false;
}
String dbName = isTemp ? SQLITE_TEMP_MASTER : SQLITE_MASTER;
String sql = "SELECT COUNT(*) FROM " + dbName + " WHERE type = ? AND name = ?";
Cursor cursor=null;
int count = 0;
try {
cursor = db.rawQuery(sql, new String[]{"table", tableName});
if (cursor == null || !cursor.moveToFirst()) {
return false;
}
count = cursor.getInt(0);
} catch (Exception e) {
e.printStackTrace();
} finally {
if (cursor != null)
cursor.close();
}
return count > 0;
}
private static String getColumnsStr(DaoConfig daoConfig) {
if (daoConfig == null) {
return "no columns";
}
StringBuilder builder = new StringBuilder();
for (int i = 0; i < daoConfig.allColumns.length; i++) {
builder.append(daoConfig.allColumns[i]);
builder.append(",");
}
if (builder.length() > 0) {
builder.deleteCharAt(builder.length() - 1);
}
return builder.toString();
}
private static void dropAllTables(Database db, boolean ifExists, @NonNull Class<? extends AbstractDao<?, ?>>... daoClasses) {
reflectMethod(db, "dropTable", ifExists, daoClasses);
printLog("【Drop all table by reflect】");
}
private static void createAllTables(Database db, boolean ifNotExists, @NonNull Class<? extends AbstractDao<?, ?>>... daoClasses) {
reflectMethod(db, "createTable", ifNotExists, daoClasses);
printLog("【Create all table by reflect】");
}
/**
* dao class already define the sql exec method, so just invoke it
*/
private static void reflectMethod(Database db, String methodName, boolean isExists, @NonNull Class<? extends AbstractDao<?, ?>>... daoClasses) {
if (daoClasses.length < 1) {
return;
}
try {
for (Class cls : daoClasses) {
Method method = cls.getDeclaredMethod(methodName, Database.class, boolean.class);
method.invoke(null, db, isExists);
}
} catch (NoSuchMethodException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
private static 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");
if (!isTableExists(db, true, tempTableName)) {
continue;
}
try {
// get all columns from tempTable, take careful to use the columns list
List<String> columns = getColumns(db, tempTableName);
ArrayList<String> properties = new ArrayList<>(columns.size());
for (int j = 0; j < daoConfig.properties.length; j++) {
String columnName = daoConfig.properties[j].columnName;
if (columns.contains(columnName)) {
properties.add("`" + columnName + "`");
}
}
if (properties.size() > 0) {
final String columnSQL = TextUtils.join(",", properties);
StringBuilder insertTableStringBuilder = new StringBuilder();
insertTableStringBuilder.append("REPLACE INTO ").append(tableName).append(" (");
insertTableStringBuilder.append(columnSQL);
insertTableStringBuilder.append(") SELECT ");
insertTableStringBuilder.append(columnSQL);
insertTableStringBuilder.append(" FROM ").append(tempTableName).append(";");
db.execSQL(insertTableStringBuilder.toString());
printLog("【Restore data】 to " + tableName);
}
StringBuilder dropTableStringBuilder = new StringBuilder();
dropTableStringBuilder.append("DROP TABLE ").append(tempTableName);
db.execSQL(dropTableStringBuilder.toString());
printLog("【Drop temp table】" + tempTableName);
} catch (SQLException e) {
Log.e(TAG, "【Failed to restore data from temp table 】" + tempTableName, e);
}
}
}
private static List<String> getColumns(Database db, String tableName) {
List<String> columns = null;
Cursor cursor = null;
try {
cursor = db.rawQuery("SELECT * FROM " + tableName + " limit 0", null);
if (null != cursor && cursor.getColumnCount() > 0) {
columns = Arrays.asList(cursor.getColumnNames());
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if (cursor != null)
cursor.close();
if (null == columns)
columns = new ArrayList<>();
}
return columns;
}
private static void printLog(String info){
if(DEBUG){
Log.d(TAG, info);
}
}
}
另外,