java - 相关实体的 GreenDao getter 返回空列表

Question

我有一个 android 应用程序，我在其中使用 greenDAO 为我的数据库建模。我有一个简单的场景，但我不明白如何让它发挥作用。我已经按照文档进行操作，但我一定遗漏了一些东西。

我有 3 个实体:用户、图片和地址。用户有图片和地址。我的 Picture 和 Address getters 总是返回 null。

    userEntity.getPicture(); -> returns null
    userEntity.getAddress(); -> returns null

这是我的 GreenDAO 设置

    Entity userEntity = schema.addEntity("User");
    userEntity.addIdProperty();
    userEntity.addStringProperty("firstName");
    userEntity.addStringProperty("lastName");

    Entity picture = schema.addEntity("Picture");
    picture.addIdProperty();
    picture.addByteArrayProperty("image");
    picture.addStringProperty("imageName");

    Entity address = schema.addEntity("Address");
    address.addIdProperty();
    address.addStringProperty("street");
    address.addIntProperty("houseNumber");
    address.addIntProperty("zipcode");
    address.addStringProperty("city");

    // a user can have multiple pictures but a picture is connected to one user
    Property pictureIdProperty = picture.addLongProperty("userId").getProperty();
    picture.addToOne(userEntity, pictureIdProperty).setName("user");
    userEntity.addToMany(picture, pictureIdProperty).setName("picture");

    // a user can have multiple addresses but an address is only connected to one user
    Property addressIdProperty = address.addLongProperty("userId").getProperty();
    address.addToOne(userEntity, addressIdProperty).setName("user");
    userEntity.addToMany(address, addressIdProperty).setName("address");

这是我测试关系的测试类

    DevOpenHelper helper = new DaoMaster.DevOpenHelper(getApplication(), "relation_test_db", null);
    SQLiteDatabase db = helper.getWritableDatabase();
    DaoMaster daoMaster = new DaoMaster(db);
    this.daoSession = daoMaster.newSession();

    UserDao userDao = this.daoSession.getUserDao();
    PictureDao pictureDao = this.daoSession.getPictureDao();
    AddressDao addressDao = this.daoSession.getAddressDao();

    // clear all data
    userDao.deleteAll();
    pictureDao.deleteAll();
    addressDao.deleteAll();

    /**
     * create data
     */
    User bill = new User(null);
    bill.setFirstName("Bill");
    bill.setLastName("Murray");

    Picture billsPicture = new Picture(null);
    billsPicture.setImage("BillsExamplePictureByteArray".getBytes());
    billsPicture.setImageName("BillsPictureName");

    Address billsAddress = new Address(null);
    billsAddress.setStreet("BillsStreet");
    billsAddress.setHouseNumber(42);
    billsAddress.setZipcode(12345);
    billsAddress.setCity("Wilmette");

    billsPicture.setUser(bill);
    billsAddress.setUser(bill);

    userDao.insert(bill);
    pictureDao.insert(billsPicture);
    addressDao.insert(billsAddress);

    User user = userDao.queryBuilder().list().get(0);
    ArrayList<Picture> billsPictureList = (ArrayList<Picture>) user.getPicture();
    ArrayList<Address> billsAddressList = (ArrayList<Address>) user.getAddress();

    if (billsPictureList == null || billsPictureList.size() == 0) {
        // contact Markus
        Toast.makeText(this, "Contact Stackoverflow", Toast.LENGTH_SHORT).show();
        return;
    }

    if (billsAddressList == null || billsAddressList.size() == 0) {
        // contact Markus
        Toast.makeText(this, "Contact Stackoverflow", Toast.LENGTH_SHORT).show();
        return;
    }

Answer 1

伊曼纽尔，

尝试保存具有一对一关系的对象时，我遇到了一些类似的问题。

在 greenDAO 上花费了相当多的时间后，我发现所有“关系”对象在保存到数据库之前都应该具有其“父级”的适当映射 ID。

所以我建议，如果您查看生成的 Picture 和 Address 实体的 setUser 方法，您会看到一些东西喜欢:

public void setUser(User user) {
    synchronized (this) {
        this.user = user;
        userId = user == null ? null : user.getId();
        user__resolvedKey = userId;
    }
}

关键是 userId = user == null ？ null : 用户.getId();

存在竞争条件，因为您创建的用户对象在实际保存到数据库之前不会获得 ID。如果它没有 ID，则它的关系实体的 setUser 有可能无法正常工作。

在您的情况下，您可以尝试将保存顺序更改为:

//1. Save user to DB, this will give it ID  
userDao.insert(bill);  

//2. Set user entity with ID to its relational entities  
billsPicture.setUser(bill);  
billsAddress.setUser(bill);  

//3. Save relational entities  
pictureDao.insert(billsPicture);  
addressDao.insert(billsAddress);

希望我的回答对您有所帮助。