GreenDao的簡單使用[二]之升級資料庫
阿新 • • 發佈:2019-01-27
寫在前面
資料庫雖然是寫在app本地用於儲存資訊等,但有時也會出現需求更新,需要增加欄位或者其他的更新情況。這時需要我們對資料庫進行更新。使用GreenDao的好處,就是暴露出來了相應的方法,我們去實現就可以了。
工具類
關於GreenDao的簡單使用,之前寫過文章了。不太瞭解的小夥伴可以去看看。GreenDao的簡單使用[一]
其中會 建立新的臨時庫、匯入資料、廢棄舊的資料庫、建立新資料庫(符合要求的)、匯入資料等操作。
所以可以建立一個Helper類來處理升級這個事情。
public class DbHelper extends DaoMaster.OpenHelper { private static String DBNAME = "user"; public DbHelper(Context context) { super(context, DBNAME, null); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { super.onUpgrade(db, oldVersion, newVersion); if (oldVersion < newVersion) { Log.i("version", oldVersion + "---比較版本---" + newVersion); MigrationHelper.getInstance().migrate(db, UserDao.class); //更改過的實體類(新增的不用加) 更新UserDao檔案 可以新增多個 XXDao.class 檔案 // MigrationHelper.getInstance().migrate(db, UserDao.class,XXDao.class); } } }
然後對java bean做處理 增加欄位等 並重新編譯 獲得如下程式碼,此時UserDao也更新了。Yeah
//新增加欄位 age
@Entity public class User { @Id private Long id; private String name; @Transient private int tempUsageCount; // not persisted private int age; public int getAge() { return this.age; } public void setAge(int age) { this.age = age; } public String getName() { return this.name; } public void setName(String name) { this.name = name; } public Long getId() { return this.id; } public void setId(Long id) { this.id = id; } @Generated(hash = 1309193360) public User(Long id, String name, int age) { this.id = id; this.name = name; this.age = age; } @Generated(hash = 586692638) public User() { } }
接著去處理一下更新。在Application中
public void setUpDatabase() { // DaoMaster.DevOpenHelper devOpenHelper = new DaoMaster.DevOpenHelper(this, DATA_NAME); DaoMaster.OpenHelper devOpenHelper = new DbHelper(new DaoUtil(this));//更新資料庫時候使用 SQLiteDatabase database = devOpenHelper.getWritableDatabase(); DaoMaster daoMaster = new DaoMaster(database); session = daoMaster.newSession(); }
附件
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.support.annotation.NonNull;
import android.text.TextUtils;
import org.greenrobot.greendao.AbstractDao;
import org.greenrobot.greendao.database.Database;
import org.greenrobot.greendao.database.StandardDatabase;
import org.greenrobot.greendao.internal.DaoConfig;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public final class MigrationHelper {
private static MigrationHelper helper = new MigrationHelper();
public static MigrationHelper getInstance() {
return helper;
}
public static void migrate(SQLiteDatabase sqliteDatabase, Class<? extends AbstractDao<?, ?>>... daoClasses) {
StandardDatabase db = new StandardDatabase(sqliteDatabase);
generateNewTablesIfNotExists(db, daoClasses);
generateTempTables(db, daoClasses);
dropAllTables(db, true, daoClasses);
createAllTables(db, false, daoClasses);
restoreData(db, daoClasses);
}
public static void migrate(StandardDatabase db, Class<? extends AbstractDao<?, ?>>... daoClasses) {
generateNewTablesIfNotExists(db, daoClasses);
generateTempTables(db, daoClasses);
dropAllTables(db, true, daoClasses);
createAllTables(db, false, daoClasses);
restoreData(db, daoClasses);
}
private static void generateNewTablesIfNotExists(StandardDatabase db, Class<? extends AbstractDao<?, ?>>... daoClasses) {
reflectMethod(db, "createTable", true, daoClasses);
}
private static void generateTempTables(StandardDatabase 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");
StringBuilder insertTableStringBuilder = new StringBuilder();
insertTableStringBuilder.append("CREATE TEMP TABLE ").append(tempTableName);
insertTableStringBuilder.append(" AS SELECT * FROM ").append(tableName).append(";");
db.execSQL(insertTableStringBuilder.toString());
}
}
private static void dropAllTables(StandardDatabase db, boolean ifExists, @NonNull Class<? extends AbstractDao<?, ?>>... daoClasses) {
reflectMethod(db, "dropTable", ifExists, daoClasses);
}
private static void createAllTables(StandardDatabase db, boolean ifNotExists, @NonNull Class<? extends AbstractDao<?, ?>>... daoClasses) {
reflectMethod(db, "createTable", ifNotExists, daoClasses);
}
/**
* dao class already define the sql exec method, so just invoke it
*/
private static void reflectMethod(StandardDatabase 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(StandardDatabase 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");
// 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("INSERT INTO ").append(tableName).append(" (");
insertTableStringBuilder.append(columnSQL);
insertTableStringBuilder.append(") SELECT ");
insertTableStringBuilder.append(columnSQL);
insertTableStringBuilder.append(" FROM ").append(tempTableName).append(";");
db.execSQL(insertTableStringBuilder.toString());
}
StringBuilder dropTableStringBuilder = new StringBuilder();
dropTableStringBuilder.append("DROP TABLE ").append(tempTableName);
db.execSQL(dropTableStringBuilder.toString());
}
}
private static List<String> getColumns(StandardDatabase 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;
}
}
DbUtil.java
//建立資料庫生成路徑
public class DaoUtil extends ContextWrapper {
private String currentUserId = "greendao";//一般用來針對一個使用者一個數據庫,以免資料混亂問題
private Context mContext;
public DaoUtil(Context base) {
super(base);
this.mContext = base;
}
/**
* 獲得資料庫路徑,如果不存在,則建立物件
*
* @param dbName
*/
@Override
public File getDatabasePath(String dbName) {
String dbDir ="/mnt/sdcard/greendao/";
if (TextUtils.isEmpty(dbDir)){
Log.e("SD卡管理:", "SD卡不存在,請載入SD卡");
return null;
}
File baseFile = new File(dbDir);
// 目錄不存在則自動建立目錄
if (!baseFile.exists()){
baseFile.mkdirs();
}
StringBuffer buffer = new StringBuffer();
buffer.append(baseFile.getPath());
buffer.append(File.separator);
buffer.append(currentUserId);
dbDir = buffer.toString();// 資料庫所在目錄
buffer.append(File.separator);
// buffer.append(dbName+"_"+currentUserId);//也可以採用此種方式,將使用者id與表名聯絡到一塊命名
buffer.append(dbName);
String dbPath = buffer.toString();// 資料庫路徑
// 判斷目錄是否存在,不存在則建立該目錄
File dirFile = new File(dbDir);
if (!dirFile.exists()){
dirFile.mkdirs();
}
// 資料庫檔案是否建立成功
boolean isFileCreateSuccess = false;
// 判斷檔案是否存在,不存在則建立該檔案
File dbFile = new File(dbPath);
if (!dbFile.exists()) {
try {
isFileCreateSuccess = dbFile.createNewFile();// 建立檔案
} catch (IOException e) {
e.printStackTrace();
}
} else
isFileCreateSuccess = true;
// 返回資料庫檔案物件
if (isFileCreateSuccess)
return dbFile;
else
return super.getDatabasePath(dbName);
}
/**
* 過載這個方法,是用來開啟SD卡上的資料庫的,android 2.3及以下會呼叫這個方法。
*
* @param name
* @param mode
* @param factory
*/
@Override
public SQLiteDatabase openOrCreateDatabase(String name, int mode, SQLiteDatabase.CursorFactory factory) {
SQLiteDatabase result = SQLiteDatabase.openOrCreateDatabase(getDatabasePath(name), factory);
return result;
}
/**
* Android 4.0會呼叫此方法獲取資料庫。
*
* @param name
* @param mode
* @param factory
* @param errorHandler
* @see ContextWrapper#openOrCreateDatabase(String, int,
* SQLiteDatabase.CursorFactory,
* DatabaseErrorHandler)
*/
@Override
public SQLiteDatabase openOrCreateDatabase(String name, int mode, SQLiteDatabase.CursorFactory factory,DatabaseErrorHandler errorHandler) {
SQLiteDatabase result = SQLiteDatabase.openOrCreateDatabase(getDatabasePath(name), factory);
return result;
}
}
寫在後面
所以使用處理資料庫使用GreenDao就會變得很便利,需要的方法框架中都幫我們整合好了。
如果寫的有什麼問題,可以留言我。我們共同進步。謝謝!
個人微信公眾號:摩羯座程式媛的日常 (dreamflower_hannah)