Android数据库GreenDAO3.2.2的使用（二，数据库使用）

GreenDao数据库依赖添加完了，表也创建好了，下一步就是创建数据库和使用数据库了。

一、创建数据库      

DaoMaster.DevOpenHelper devOpenHelper=new DaoMaster.DevOpenHelper(context,"test.db");
SQLiteDatabase database = devOpenHelper.getWritableDatabase();
DaoSession daoSession = new DaoMaster(database).newSession();
QuestionDao questionDao = daoSession.getQuestionDao();

这样一个数据库就生成了，当我们获取 questionDao 对象之后，就能非常方便的操作数据库了。

我这里是通过创建一个单例来管理数据库：

/**
 * 数据库操作类
 * Created by KingsleyCheng on 2017/5/11.
 */

public class GreenDaoUtils {
    private MySQLiteOpenHelper mHelper;
    private SQLiteDatabase db;
    private DaoMaster mDaoMaster;
    private DaoSession mDaoSession;

    private static class GreenDaoUtilsHolder {
        private static final GreenDaoUtils INSTANCE = new GreenDaoUtils();
    }

    private GreenDaoUtils() {
    }

    public static GreenDaoUtils getSingleton() {
        return GreenDaoUtilsHolder.INSTANCE;
    }

    private void initGreenDao() {
        mHelper = new MySQLiteOpenHelper(BaseApplication.getApplication(), 
                "test-db", null);
        db = mHelper.getWritableDatabase();
        mDaoMaster = new DaoMaster(db);
        mDaoSession = mDaoMaster.newSession();
    }

    public DaoSession getDaoSession() {
        if (mDaoMaster == null) {
            initGreenDao();
        }
        return mDaoSession;
    }
 

   /**
     * 获取可写数据库

     */

public SQLiteDatabase getDb() { if ( db == null) { initGreenDao() ; } return db ; }

}

MySQLiteOpentHelper是为了解决数据库升级数据丢失自定义的一个类，继承于DoMaster.OpenHelper类（会单独介绍的）：

public class MySQLiteOpenHelper extends DaoMaster.OpenHelper {

数据库管理者单例构建完成后，在application里面注册数据库：

@Override
public void onCreate() {
    super.onCreate();
    baseApplication = this;
    GreenDaoUtils. getSingleton();//数据库初始化
}

这样数据库就构建完成了。

二、数据库的基本操作：

1. 增

mUser = new User((long)2,"anye3");
mUserDao.insert(mUser);//添加一个

2. 删

mUserDao.deleteByKey(id);

3. 改

mUser = new User((long)2,"anye0803");
mUserDao.update(mUser);

4. 查

List users = mUserDao.loadAll();
String userName = "";
for (int i = 0; i < users.size(); i++) {
    userName += users.get(i).getName()+",";
}
mContext.setText("查询全部数据==>"+userName);
这些方法都可以写在数据库管理单例里GreenDaoUtils面：

/**
 * 插入一条记录
 *
 * @param user
 */
public void insertUser(User user) {
    DaoMaster daoMaster = new DaoMaster(getWritableDatabase());
    DaoSession daoSession = daoMaster.newSession();
    UserDao userDao = daoSession.getUserDao();
    userDao.insert(user);
}


/**
 * 插入用户集合
 *
 * @param users
 */
public void insertUserList(List users) {
    if (users == null || users.isEmpty()) {
        return;
    }
    DaoMaster daoMaster = new DaoMaster(getWritableDatabase());
    DaoSession daoSession = daoMaster.newSession();
    UserDao userDao = daoSession.getUserDao();
    userDao.insertInTx(users);
}


/**
 * 删除一条记录
 *
 * @param user
 */
public void deleteUser(User user) {
    DaoMaster daoMaster = new DaoMaster(getWritableDatabase());
    DaoSession daoSession = daoMaster.newSession();
    UserDao userDao = daoSession.getUserDao();
    userDao.delete(user);
}

/**
 * 更新一条记录
 *
 * @param user
 */
public void updateUser(User user) {
    DaoMaster daoMaster = new DaoMaster(getWritableDatabase());
    DaoSession daoSession = daoMaster.newSession();
    UserDao userDao = daoSession.getUserDao();
    userDao.update(user);
}

/**
 * 查询用户列表
 */
public List queryUserList() {
    DaoMaster daoMaster = new DaoMaster(getReadableDatabase());
    DaoSession daoSession = daoMaster.newSession();
    UserDao userDao = daoSession.getUserDao();
    QueryBuilder qb = userDao.queryBuilder();
    List list = qb.list();
    return list;
}

/**
 * 查询用户列表
 */
public List queryUserList(int age) {
    DaoMaster daoMaster = new DaoMaster(getReadableDatabase());
    DaoSession daoSession = daoMaster.newSession();
    UserDao userDao = daoSession.getUserDao();
    QueryBuilder qb = userDao.queryBuilder();
    qb.where(UserDao.Properties.Age.gt(age)).orderAsc(UserDao.Properties.Age);
    List list = qb.list();
    return list;
}

当然也可以使用insertOrReplace代替insert，更多的方法大家可以自己查询资料或者查询源码来研究。

void addUserList(List lists) {
    getDaoSession().getUserListDao().insertOrReplaceInTx(lists);
}

还可以使用SQL语句查询：

cursor = GreenDaoUtils. getSingleton().getDb().rawQuery("SQL语句", null);

二、使用数据库查询数据，并获取数据（我的项目需求使用的是SQL语句查询的）：

try {
//            cursor = mDaoSession.getDatabase().rawQuery(SQLValues.SQL_PROJECT,
                    new String[]{Preferences.getUserID()});
            cursor = GreenDaoUtils.getSingleton().getDb()
                .rawQuery(SQLValues.SQL_PROJECT, new String[]{Preferences.getUserID()});
            while (cursor.moveToNext()) {
                projectList = new ProjectList();
                projectList.setProjectId(cursor.getString(
                            cursor.getColumnIndex("projectId")));
                projectList.setProjectName(cursor.getString(
                            cursor.getColumnIndex("projectName")));
                projectLists.add(projectList);
            }
            projectMessage.setProjectList(projectLists);
            setListView(projectMessage);
        } catch (RuntimeException e) {
            Log.d("SlidingMyProjectListFra", e.getMessage());
        } finally {
            if (cursor != null) {
                cursor.close();
            }
        }

大家可以根据自己项目需求灵活运用。