[置顶] （二）GreenDao3.0的数据库升级

public class MigrationHelper {
/**
* 调用升级方法
* @param db
* @param daoClasses 一系列dao.class
*/
public static void migrate(Database db, Class<? extends AbstractDao<?, ?>>... daoClasses) {
//1 新建临时表
generateTempTables(db, daoClasses);
//2 创建新表
createAllTables(db, false, daoClasses);
//3 临时表数据写入新表，删除临时表
restoreData(db, daoClasses);
}

/**
* 生成临时表，存储旧的表数据
* @param db
* @param daoClasses
*/
private static void generateTempTables(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;
if (!checkTable(db,tableName))
continue;
String tempTableName = daoConfig.tablename.concat("_TEMP");
StringBuilder insertTableStringBuilder = new StringBuilder();
insertTableStringBuilder.append("alter table ")
.append(tableName)
.append(" rename to ")
.append(tempTableName)
.append(";");
db.execSQL(insertTableStringBuilder.toString());
}
}

/**
* 检测table是否存在
* @param db
* @param tableName
*/
private static Boolean checkTable(Database db,String  tableName){
StringBuilder query = new StringBuilder();
query.append("SELECT count(*) FROM sqlite_master WHERE type='table' AND name='").append(tableName).append("'");
Cursor c = db.rawQuery(query.toString(), null);
if (c.moveToNext()){
int count = c.getInt(0);
if(count>0){
return true;
}
return false;
}
return false;
}

/**
* 删除所有旧表
* @param db
* @param ifExists
* @param daoClasses
*/
private static void dropAllTables(Database db, boolean ifExists, @NonNull Class<? extends AbstractDao<?, ?>>... daoClasses) {
reflectMethod(db, "dropTable", ifExists, daoClasses);
}

/**
* 创建新的表结构
* @param db
* @param ifNotExists
* @param daoClasses
*/
private static void createAllTables(Database db, boolean ifNotExists, @NonNull Class<? extends AbstractDao<?, ?>>... daoClasses) {
reflectMethod(db, "createTable", ifNotExists, daoClasses);
}

/**
* 创建根删除都在NoteDao声明了，可以直接拿过来用
* 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) {
//根据方法名，找到声明的方法
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();
}
}

/**
* 临时表的数据写入新表
* @param db
* @param daoClasses
*/
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 (!checkTable(db,tempTableName))
continue;
// get all columns from tempTable, take careful to use the columns list
List<String> columns = getColumns(db, tempTableName);
//新表，临时表都包含的字段
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(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;
}

}

public class DBHelper extends DaoMaster.OpenHelper {
public static final String DBNAME = "lenve.db";

public DBHelper(Context context) {
super(context, "lenovo.db", null);
}

@Override
public void onUpgrade(Database db, int oldVersion, int newVersion) {
super.onUpgrade(db, oldVersion, newVersion);
MigrationHelper.migrate(db,CommentDao.class);//可以写多个Dao类。
}
}