android - ORMLite 中的集合

Question

你好 我想在我的 android 应用程序中使用 ORMlite 保留一些集合数据。例如:

class Person {
  @DatabaseField(generatedId=true)
  private int id;

  @DatabaseField
  private String name;

  @DatabaseField
  private String surname;

  @ForeignCollectionField
  private Collections<Phone> phones;
}

class Phone {
  @DatabaseField(generatedId=true)
  private int id;

  @DatabaseField
  private String number;

  @DatabaseField
  private String type; 
}

我应该怎么做才能持久保存这个集合。

编辑

我按照您告诉我的那样使用 ForeignCollectionField。但是现在我有另一个问题 - 是否可以像那样构造(我稍微改变了类)

@DatabaseTable
public class Student {

    @DatabaseField(generatedId=true)
    private int id;

    @DatabaseField
    private String name;

    @DatabaseField
    private String surname;

    @DatabaseField
    private String semestr;

    @ForeignCollectionField
    private Collection<Adres> adres;
}

public class Adres implements Serializable {

    @DatabaseField(generatedId=true)
    private int id;

    @DatabaseField(foreign=true, columnName="student_id")
    private Student student;

    @DatabaseField
    private String miasto;

    @DatabaseField
    private String ulica;

    @DatabaseField
    private String nr;

    @ForeignCollectionField
    private Collection<Phone> phone;
}

public class Phone {

    @DatabaseField(generatedId=true)
    private int id;

    @DatabaseField
    private String number;

    @DatabaseField(foreign=true, columnName="adres_id" )
    private Adres adres;
}

我构建了这个结构，我把它放在 3 个表格中。

Student queryForStudentMarcin = simpleDao.queryForId(studentMarcin.getId());
Collection<Adres> adres = queryForStudentMarcin.getAdres();

for (Adres a : adres) {
    int id = a.getId();
    String miasto = a.getMiasto();
    String ulica = a.getUlica();
    String nr = a.getNr();
}

然后我这样做并出现错误:

04-03 15:55:58.392: ERROR/AndroidRuntime(6506): FATAL EXCEPTION: main
04-03 15:55:58.392: ERROR/AndroidRuntime(6506): java.lang.NullPointerException
04-03 15:55:58.392: ERROR/AndroidRuntime(6506):     at com.j256.ormlite.field.FieldType.buildForeignCollection(FieldType.java:579)
04-03 15:55:58.392: ERROR/AndroidRuntime(6506):     at com.j256.ormlite.stmt.mapped.BaseMappedQuery.mapRow(BaseMappedQuery.java:58)
04-03 15:55:58.392: ERROR/AndroidRuntime(6506):     at com.j256.ormlite.stmt.SelectIterator.nextThrow(SelectIterator.java:107)
04-03 15:55:58.392: ERROR/AndroidRuntime(6506):     at com.j256.ormlite.stmt.SelectIterator.next(SelectIterator.java:120)
04-03 15:55:58.392: ERROR/AndroidRuntime(6506):     at com.example.orm.MainActivity.dodajDoBazyCollection(MainActivity.java:140)
04-03 15:55:58.392: ERROR/AndroidRuntime(6506):     at com.example.orm.MainActivity$2.onClick(MainActivity.java:66)
04-03 15:55:58.392: ERROR/AndroidRuntime(6506):     at android.view.View.performClick(View.java:2408)
04-03 15:55:58.392: ERROR/AndroidRuntime(6506):     at android.view.View$PerformClick.run(View.java:8816)
04-03 15:55:58.392: ERROR/AndroidRuntime(6506):     at android.os.Handler.handleCallback(Handler.java:587)
04-03 15:55:58.392: ERROR/AndroidRuntime(6506):     at android.os.Handler.dispatchMessage(Handler.java:92)
04-03 15:55:58.392: ERROR/AndroidRuntime(6506):     at android.os.Looper.loop(Looper.java:123)
04-03 15:55:58.392: ERROR/AndroidRuntime(6506):     at android.app.ActivityThread.main(ActivityThread.java:4627)
04-03 15:55:58.392: ERROR/AndroidRuntime(6506):     at java.lang.reflect.Method.invokeNative(Native Method)
04-03 15:55:58.392: ERROR/AndroidRuntime(6506):     at java.lang.reflect.Method.invoke(Method.java:521)
04-03 15:55:58.392: ERROR/AndroidRuntime(6506):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
04-03 15:55:58.392: ERROR/AndroidRuntime(6506):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
04-03 15:55:58.392: ERROR/AndroidRuntime(6506):     at dalvik.system.NativeStart.main(Native Method)

有什么建议吗？

编辑2

问题是从数据库中读取数据。这个程序工作正常，现在很好，但我只是用它来理解 ORMlite。非常感谢 Gray 的帮助。

protected void czytajZBazy() throws SQLException {

    Dao<Student, Integer> simpleDao = getHelper().getSimpleDao();
    Dao<Adres, Integer> adresDao = getHelper().getAdresDao();
    Dao<Phone, Integer> phoneDao = getHelper().getPhoneDao();

    /**
     * wyswietl adresy dla studenta Marcin
     */
    QueryBuilder<Student, Integer> qbStudent = simpleDao.queryBuilder();;
    Where<Student, Integer> where = qbStudent.where();
    where.eq("name", "Marcin");
    PreparedQuery<Student> prepare = qbStudent.prepare();
    CloseableIterator<Student> iterator = simpleDao.iterator(prepare);
    while(iterator.hasNext()){
        Log.v("inside ", "loop");
        Student next = iterator.next();
        Log.v("sudent", ""+next.getId()+" "+next.getName()+" "+next.getSurname());

        QueryBuilder<Adres, Integer> adresQB = adresDao.queryBuilder();
        Where<Adres, Integer> where2 = adresQB.where();

        where2.eq("student_id", next.getId());

        PreparedQuery<Adres> preparedAdres = adresQB.prepare();
        CloseableIterator<Adres> iterator2 = adresDao.iterator(preparedAdres);

        while(iterator2.hasNext()){
            Log.v("iterator po adresie", "!!");
            Adres nextAdres = iterator2.next();
            Log.v("Adres", ""+nextAdres.getId()+" "+nextAdres.getMiasto());
            //wypisz telefony 
            QueryBuilder<Phone, Integer> queryPhone = phoneDao.queryBuilder();
            Where<Phone, Integer> where3 = queryPhone.where();
            where3.eq("adres_id", nextAdres.getId());

            PreparedQuery<Phone> preparedPhone = queryPhone.prepare();
            CloseableIterator<Phone> iterator3 = phoneDao.iterator(preparedPhone);

            while(iterator3.hasNext()){
                Log.v("inside phone iterator", "");
                Phone next2 = iterator3.next();
                Log.v("phone", ""+next2.getId()+" "+next2.getNumber());
            }
            iterator3.close();
        }
        iterator2.close();
    }
    iterator.close();
}

Answer 1

有许多资源和手册可以帮助在 Android 下使用 ORMLite。

http://ormlite.com/docs/android
http://ormlite.com/docs/android-examples

要持久化一个集合，您必须首先为该类获取一个 Dao，然后使用该 Dao 创建每个对象:

Dao<Person, Integer> personDao =
    DaoManager.createDao(androidConnectionSource, Person.class);
for (Person person : personCollection) {
    personDao.create(person);
}

您的 Phone 类也几乎相同。

---

他实际上是在询问如何使用 ORMLite 的 ForeignCollectionField 特性。可以在此处找到相关文档:

http://ormlite.com/docs/foreign-collection

还有一个使用它的示例项目。在上面的示例中，您缺少 Phone 中的 Person 字段。如果这个人有电话对象的集合，那么每个电话对象都需要有一个对应的人。这在 ORMLite 中称为“外部对象”。

http://ormlite.com/docs/foreign-object