GreenDao 学习笔记 5

简介

这篇将介绍 GreenDao 中的双向关联和那啥。

双向关联

hibernate 中是使用 mapped by 注解来实现双向关联的。

而在 GreenDao 中，双向关联就是两次单项关联而已。

 public static void main(String[] args) throws Exception {        Schema schema = new Schema(1, "com.example.GreenDao5");        Entity customerEntity = schema.addEntity("Customer");        customerEntity.addIdProperty();        customerEntity.addStringProperty("name").notNull();        Entity orderEntity = schema.addEntity("Orders");  // order 是关键字        orderEntity.addIdProperty();        orderEntity.addStringProperty("name").notNull();        Property customerIdProperty = orderEntity.addLongProperty("customerId").notNull().getProperty();        customerEntity.addToMany(orderEntity, customerIdProperty);        orderEntity.addToOne(customerEntity,customerIdProperty);        new DaoGenerator().generateAll(schema, "D:\\");    }

那啥

就是树形结构，表结构是递归表，有一个 parentId 的字段。

GreenDao 每个Relation 必须有唯一的名称，所以这里通过 setName 覆盖了。

 public static void main(String[] args) throws Exception {        Schema schema = new Schema(1, "com.example.GreenDao5");        Entity personEntity = schema.addEntity("Person");        personEntity.addIdProperty();        personEntity.addStringProperty("name").notNull();        Property parentIdProperty = personEntity.addLongProperty("parentId").getProperty();        personEntity.addToOne(personEntity, parentIdProperty).setName("parent");        personEntity.addToMany(personEntity, parentIdProperty).setName("children");        new DaoGenerator().generateAll(schema, "D:\\");    }

ListViewAdapter.java

public class ListViewAdapter extends BaseAdapter {    private List<Person> data = new ArrayList<Person>();    private LayoutInflater layoutInflater;    public ListViewAdapter(Activity activity) {        layoutInflater = activity.getLayoutInflater();    }    @Override    public int getCount() {        return data.size();    }    @Override    public View getView(int position, View convertView, ViewGroup parent) {        Person person = data.get(position);        String text = person.getName() + "\r\n";        person.resetChildren();        for (Person child : person.getChildren()) {            text += (child.getName() + "");        }        TextView textView = (TextView) layoutInflater.inflate(R.layout.listview_item, parent, false);        textView.setText(text);        return textView;    }    public List<Person> getData() {        return data;    }    @Override    public Object getItem(int position) {        return null;    }    @Override    public long getItemId(int position) {        return 0;    }}

所有 GreenDao 产生的实体，都是默认缓存的，想要取得当前数据库的数据，需要 reset 一下。

my_activity.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"              android:orientation="vertical"              android:layout_width="match_parent"              android:layout_height="match_parent">    <LinearLayout android:layout_width="match_parent"                  android:layout_height="50dp"                  android:orientation="horizontal">        <EditText android:id="@+id/etPersonName"                  android:layout_weight="1" android:layout_width="0dp"                  android:layout_height="match_parent"                  android:hint="人名"/>        <Button android:id="@+id/btnAdd"                android:layout_width="wrap_content"                android:layout_height="match_parent"                android:text="添加"/>    </LinearLayout>    <ListView android:id="@+id/lvNote"              android:layout_width="match_parent"              android:layout_height="0dp" android:layout_weight="1"/></LinearLayout>

MyActivity.java

public class MyActivity extends Activity implements View.OnClickListener, AdapterView.OnItemClickListener {    private PersonDao personDao;    private ListViewAdapter listViewAdapter;    private EditText etPersonName;    // 顶层节点的 parentId 为 -1    private final long DEFAULT_PARENT_ID = -1L;    // 默认创建顶层节点    private Long parentId = DEFAULT_PARENT_ID;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.my_activity);        initDao();        initView();        refreshListView();    }    @Override    public void onClick(View v) {        onBtnAddClick();    }    @Override    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {        onListViewItemClick(position);    }    private void initDao() {        DaoMaster.DevOpenHelper helper = new DaoMaster.DevOpenHelper(this, "person-db", null);        SQLiteDatabase db = helper.getWritableDatabase();        DaoMaster daoMaster = new DaoMaster(db);        DaoSession daoSession = daoMaster.newSession();        personDao = daoSession.getPersonDao();    }    private void initView() {        etPersonName = (EditText) findViewById(R.id.etPersonName);        findViewById(R.id.btnAdd).setOnClickListener(this);        ListView listView = (ListView) findViewById(R.id.lvNote);        listViewAdapter = new ListViewAdapter(this);        listView.setAdapter(listViewAdapter);        listView.setOnItemClickListener(this);    }    private void refreshListView() {        // 注意，GreenDao 默认的查询都是懒加载        List<Person> dataFromDb = personDao._queryPerson_Children(DEFAULT_PARENT_ID);        List<Person> listViewData = listViewAdapter.getData();        listViewData.clear();        listViewData.addAll(dataFromDb);        listViewAdapter.notifyDataSetChanged();    }    private void onBtnAddClick() {        String personName = etPersonName.getText().toString();        if (personName.equals("")) {            return;        }        Person person = new Person(null, personName, parentId);        personDao.insert(person);        refreshListView();    }    private void onListViewItemClick(int position) {        Person person = listViewAdapter.getData().get(position);        parentId = person.getId();        Log.e("result", "parentId: " + parentId);    }}

小结

这样一来，GreenDao 中所有的 Relation 都已经实践过一遍了，如果需要更多的例子

https://github.com/greenrobot/greenDAO/tree/master/DaoGenerator 

https://github.com/greenrobot/greenDAO/tree/master/DaoTest