GreenDao3.2.2建立多表之间的关联

本文主要是介绍GreenDao3.2.2建立多表之间的关联，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

在上一篇文章GreenDao保存List<String>类型数据中，

介绍了如何使用GreenDao保存List<String>类型的数据， 但是在实际开发中经常会遇到List的泛型并不是String类型的，而是另外一种自定义的Bean类类型。 
比如，在上一篇文章中的User代表一个用户，但是在每一个用户中可能会保存一个订单的集合–List. 那么这种情况就需要创建多个表格，并建立关系了。 
这篇文章主要以介绍如何使用ToMany来建立两张表格之间的关系

废话不多说，直接上代码

先创建MyOrder.java

@Entity
public class MyOrder {@Id(autoincrement = true)private Long id;@Property(nameInDb = "date")private String date;@Property(nameInDb = "customId")private Long customId;@Generated(hash = 1011091970)public MyOrder(Long id, String date, Long customId) {this.id = id;this.date = date;this.customId = customId;}@Generated(hash = 191667629)public MyOrder() {}public Long getId() {return this.id;}public void setId(Long id) {this.id = id;}public String getDate() {return this.date;}public void setDate(String date) {this.date = date;}public Long getCustomId() {return this.customId;}public void setCustomId(Long customId) {this.customId = customId;}}

其中customId，会用User的主键来当做此表的外键

然后再修改一下之前的User.java, 如下所示：

/*** Created by Danny.姜 on 17/6/20.** @Entity 用于标识这是一个需要Greendao帮我们生成代码的bean* @Id 标明主键，括号里可以指定是否自增* @Property 用于设置属性在数据库中的列名（默认不写就是保持一致）* @NotNull 非空*/@Entity   //  用于标识这是一个需要Greendao帮我们生成代码的bean
public class User {@Id(autoincrement = true)private Long id;@Property(nameInDb = "user_name")@NotNullprivate String name;@Convert(columnType = String.class, converter = StringConverter.class)private List<String> nickNames;@Transientprivate int temp;@ToMany(referencedJoinProperty = "customId")private List<MyOrder> orders;/** Used for active entity operations. */@Generated(hash = 1507654846)private transient UserDao myDao;/** Used to resolve relations */@Generated(hash = 2040040024)private transient DaoSession daoSession;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;}public List<String> getNickNames() {return this.nickNames;}public void setNickNames(List<String> nickNames) {this.nickNames = nickNames;}/*** Convenient call for {@link org.greenrobot.greendao.AbstractDao#refresh(Object)}.* Entity must attached to an entity context.*/@Generated(hash = 1942392019)public void refresh() {if (myDao == null) {throw new DaoException("Entity is detached from DAO context");}myDao.refresh(this);}/*** Convenient call for {@link org.greenrobot.greendao.AbstractDao#update(Object)}.* Entity must attached to an entity context.*/@Generated(hash = 713229351)public void update() {if (myDao == null) {throw new DaoException("Entity is detached from DAO context");}myDao.update(this);}/*** Convenient call for {@link org.greenrobot.greendao.AbstractDao#delete(Object)}.* Entity must attached to an entity context.*/@Generated(hash = 128553479)public void delete() {if (myDao == null) {throw new DaoException("Entity is detached from DAO context");}myDao.delete(this);}/** Resets a to-many relationship, making the next get call to query for a fresh result. */@Generated(hash = 1446109810)public synchronized void resetOrders() {orders = null;}/*** To-many relationship, resolved on first access (and after reset).* Changes to to-many relations are not persisted, make changes to the target entity.*/@Generated(hash = 1892052450)public List<MyOrder> getOrders() {if (orders == null) {final DaoSession daoSession = this.daoSession;if (daoSession == null) {throw new DaoException("Entity is detached from DAO context");}MyOrderDao targetDao = daoSession.getMyOrderDao();List<MyOrder> ordersNew = targetDao._queryUser_Orders(id);synchronized (this) {if(orders == null) {orders = ordersNew;}}}return orders;}/** called by internal mechanisms, do not call yourself. */@Generated(hash = 2059241980)public void __setDaoSession(DaoSession daoSession) {this.daoSession = daoSession;myDao = daoSession != null ? daoSession.getUserDao() : null;}@Generated(hash = 411979277)public User(Long id, @NotNull String name, List<String> nickNames) {this.id = id;this.name = name;this.nickNames = nickNames;}@Generated(hash = 586692638)public User() {}
}

其中orders是List< MyOrder>类型，因此需要建立oMany的关系。 
使用@ToMany(referencedJoinProperty = “customId”)表示在MyOrder表中可以创建多条记录，同时customId是同样的

具体使用

重新整理布局文件：

<?xml version="1.0" encoding="utf-8"?>
<ScrollViewxmlns:android="http://schemas.android.com/apk/res/android"android:layout_width="match_parent"android:layout_height="match_parent"><LinearLayoutandroid:layout_width="match_parent"android:layout_height="match_parent"android:orientation="vertical"><EditTextandroid:id="@+id/editUserName"android:hint="please input user name"android:layout_width="match_parent"android:layout_height="wrap_content" /><EditTextandroid:id="@+id/editUserNickName1"android:hint="please input user name"android:layout_width="match_parent"android:layout_height="wrap_content" /><EditTextandroid:id="@+id/editUserNickName2"android:hint="please input user name"android:layout_width="match_parent"android:layout_height="wrap_content" /><Buttonandroid:text="创建数据库"android:onClick="createDatabase"android:layout_width="match_parent"android:layout_height="wrap_content" /><Buttonandroid:text="插入数据"android:onClick="insert"android:layout_width="match_parent"android:layout_height="wrap_content" /><Buttonandroid:text="查询数据"android:onClick="query"android:layout_width="match_parent"android:layout_height="wrap_content" /><Buttonandroid:text="查询所有"android:onClick="queryAllOrders"android:layout_width="match_parent"android:layout_height="wrap_content" /><ListViewandroid:id="@+id/listView"android:layout_width="match_parent"android:layout_height="match_parent"></ListView></LinearLayout>
</ScrollView>

修改MainActivity.java如下：

public class MainActivity extends AppCompatActivity {private DaoMaster daoMaster;private DaoSession daoSession;private UserDao userDao;private EditText editName;private ListView listView;private ArrayAdapter<String> adapter;private List<String> list = new ArrayList<>();private EditText editNickName1;private EditText editNickName2;private MyOrderDao orderDao;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);editName = ((EditText) findViewById(R.id.editUserName));editNickName1 = ((EditText) findViewById(R.id.editUserNickName1));editNickName2 = ((EditText) findViewById(R.id.editUserNickName2));listView = ((ListView) findViewById(R.id.listView));adapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1, list);listView.setAdapter(adapter);}public void createDatabase(View view) {DaoMaster.DevOpenHelper helper = new DaoMaster.DevOpenHelper(this, "user.db");daoMaster = new DaoMaster(helper.getWritableDb());daoSession = daoMaster.newSession();userDao = daoSession.getUserDao();orderDao = daoSession.getMyOrderDao();}public void insert(View view) {User user = new User();user.setName(editName.getText().toString());List<String> nickNames = new ArrayList<>();String nickName1 = editNickName1.getText().toString();String nickName2 = editNickName2.getText().toString();nickNames.add(nickName1);nickNames.add(nickName2);user.setNickNames(nickNames);long insertID = userDao.insert(user);if (insertID >= 0) {Toast.makeText(this, "插入 User 成功", Toast.LENGTH_SHORT).show();insertOrders(insertID);} else {Toast.makeText(this, "插入User 失败", Toast.LENGTH_SHORT).show();}}private void insertOrders(long userId) {MyOrder myOrder1 = new MyOrder(null, new Date() + "", userId);MyOrder myOrder2 = new MyOrder(null, new Date() + "", userId);long orderId1 = orderDao.insert(myOrder1);long orderId2 = orderDao.insert(myOrder2);if (orderId1 >= 0 && orderId2 >= 0) {Toast.makeText(this, "插入 MyOrder 成功", Toast.LENGTH_SHORT).show();}}public void query(View view) {List<User> users = userDao.queryBuilder().list();list.clear();for (User user : users) {String name = user.getName();List<String> nickNames = user.getNickNames();for (String nickName : nickNames) {Log.e("TAG", "query " + name + " : " + nickName);}list.add(user.getName());}adapter.notifyDataSetChanged();}public void queryAllOrders(View view) {List<User> users = userDao.loadAll();for (User user : users) {List<MyOrder> orders = user.getOrders();for (MyOrder order : orders) {Log.e("TAG", "get user " + user.getName() + " order " + order.getDate());}}}
}

解释一下：在insert方法中当插入User数据成功之后会拿到一个插入的ID，然后拿着这个ID，向MyOrder表格中插入两条MyOrder的数据。

运行成功之后，看一下数据库中的数据内容如下： 

 

可以看到在user.db中会创建USER和MY_ORDER两张表格

USER表格内容如下： 

 

在USER表格中存在两条记录，ID分别是1，2 名字依次是danny， jiang

MY_ORDER表格内容如下： 

 

因为有两条User的记录，每一个User又有两条Order的记录。 因此在MY_ORDER表格中存在4条记录主键是1,2,3,4 但是customId只有1和2

GreenDao另外一个强大的地方就在于建立多表关联之后， 查询数据也会方便很多。

我们知道在User中保存了List< MyOrder>的集合， 那我在查处所有的User集合之后，在这些User数据集合中会有MyOrder的数据吗？？ 答案是肯定的 
在queryAllOrders方法中我查询的事UserDao中的数据，但是通过此UserDao还是能获取MyOrder的信息，打印log如下所示： 

具体使用方式，可以参考GreenDaoDemos ： GreenDaoDemos

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