在上一章GreenDao3.0学习(二)中，我们知道了怎么使用greendao创建数据，这一章主要是介绍greendao的增删改查
增加
代码如下：
private void insertUser(Long id, String name) {
UserBeanDao userDao = GreenDaoManager.getInstance().getSession().getUserBeanDao();
UserBean user = new UserBean(id, name);
userDao.insert(user);
mNameET.setText("");
mUserList.clear();
mUserList.addAll(userDao.queryBuilder().build().list());
mUserAdapter.notifyDataSetChanged();
}没错，就是这么简单：
这里需要注意的是：insertUser中的id我们只要传null就行，比如insertUser(null, str);
看看效果：
插入成功：
删除
private void deleteUser(String name) {
UserBeanDao userBeanDao = GreenDaoManager.getInstance().getSession().getUserBeanDao();
//删除
UserBean findUser = userBeanDao.queryBuilder().where(UserBeanDao.Properties.Name.eq(name)).build().unique();
if (findUser != null) {
userBeanDao.deleteByKey(findUser.getId());
}
// //根据某一个条件批量删除
// List<UserBean> userList = userBeanDao.queryBuilder().where(UserBeanDao.Properties.Name.eq(name)).build().list();
// for (UserBean user : userList) {
// userBeanDao.delete(user);
// }
mNameET.setText("");
mUserList.clear();
mUserList.addAll(userBeanDao.queryBuilder().build().list());
mUserAdapter.notifyDataSetChanged();
}根据name删除单个：
根据name批量删除：
修改/更新
private void updateUser(String prevName, String newName) {
UserBeanDao userBeanDao = GreenDaoManager.getInstance().getSession().getUserBeanDao();
//更新单个
UserBean findUser = GreenDaoManager.getInstance().getSession().getUserBeanDao().queryBuilder()
.where(UserBeanDao.Properties.Name.eq(prevName)).build().unique();
if (findUser != null) {
findUser.setName(newName);
GreenDaoManager.getInstance().getSession().getUserBeanDao().update(findUser);
Toast.makeText(MyApplication.getContext(), "修改成功", Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(MyApplication.getContext(), "用户不存在", Toast.LENGTH_SHORT).show();
}
//批量更新
// List<UserBean> userList = userBeanDao.queryBuilder().where(UserBeanDao.Properties.Name.eq(prevName)).build().list();
// Log.e("userList", userList + "");
// if (userList.isEmpty()) {
// Toast.makeText(MyApplication.getContext(), "用户不存在", Toast.LENGTH_SHORT).show();
// } else {
// for (UserBean user : userList) {
// user.setName(newName);
// userBeanDao.update(user);
// Log.e("修改", "修改成功");
// }
// Toast.makeText(MyApplication.getContext(), "更新成功", Toast.LENGTH_SHORT).show();
// }
mNewNameET.setText("");
mNameET.setText("");
mUserList.clear();
mUserList.addAll(userBeanDao.queryBuilder().build().list());
mUserAdapter.notifyDataSetChanged();
}
单个更新
批量更新
查询
private void initData() {
mUserList = GreenDaoManager.getInstance().getSession().getUserBeanDao().queryBuilder().build().list();
mUserAdapter = new UserAdapter(this, mUserList);
mUserLV.setAdapter(mUserAdapter);
}没错，就是这么愉快的就搞定了~~~
等等，好像有一个问题，当我们升级数据库版本时，发现，以前保存的数据不见了，啊啊啊~~~咋个搞，，我们去查看代码，发现在DaoMaster.java中有这个一段更新代码
/** 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);
}
}
}q其中的注释WARNING: Drops all table on Upgrade! Use only during development.
翻译过来就是：
警告：删除所有升级的表！仅在开发过程中使用。
这可咋个搞，于是在网上找到了一种解决方案：将以前的表变为临时表，然后创建新表，将临时表中的数据拷贝过来，删除临时表。
就是自己重新添加一个新类继承DaoMaster.OpenHelper，然后自己重新实现onUpgrade方法,
代码如下：
MySQLiteOpenHelper.java
public class MySQLiteOpenHelper extends DaoMaster.OpenHelper {
public MySQLiteOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory) {
super(context, name, factory);
}
/**
* 数据库升级
*
* @param db
* @param oldVersion
* @param newVersion
*/
@Override
public void onUpgrade(Database db, int oldVersion, int newVersion) {
//操作数据库的更新
MigrationHelper.migrate(db,UserBeanDao.class,UserBean1Dao.class,UserBean3Dao.class,SiteDao.class);
}
}
MigrationHelper.java
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) {
//方法2
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;
}
}
创建数据库的方式变更为：
//创建一个数据库
MySQLiteOpenHelper helper = new MySQLiteOpenHelper(MyApplication.getContext(), "greendao-db", null);
DaoMaster mDaoMaster = new DaoMaster(helper.getWritableDatabase());
mDaoSession = mDaoMaster.newSession();
android
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