Android Realm 处理关系对象中的主键

Question

我有两个对象:MailBox 和 Email。每个 Receiver 都有很多 Emails。

public class MailBoxRealmModel extends RealmObject {

    @PrimaryKey
    private long id;

    private String name;
    private String mailboxId;
    private RealmList<EmailRealmModel> emails;
}

public class EmailRealmModel extends RealmObject {

    @PrimaryKey
    private long EmailId;

    private String Name;
    private String Text;
    private String Tag;
    private int Type;
    private String Time;
    private int Status;
}

如何在向 MailBoxRealmModel 添加电子邮件时使用 **realm.insertOrUpdate**？

EmailRealmModel email = new EmailRealmModel();
email.setMessageId(emailID);

realm.insertOrUpdate(email );

mailBoxRealmModel.getEmails().add(email);

我在这一行收到一个空指针异常 email:

mailBoxRealmModel.getEmails().add(email);

异常(exception):

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean io.realm.RealmList.add(io.realm.RealmModel)' on a null object reference at com.koa.mailbox.MailBoxActivity$1.execute(MailBoxActivity.java:123) at io.realm.Realm.executeTransaction(Realm.java:1253) at com.koa.mailbox.MailBoxActivity.test(MailBoxActivity.java:88) at com.koa.mailbox.MailBoxActivity.onCreate(MailBoxActivity.java:71) at android.app.Activity.performCreate(Activity.java:6876) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1135) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3207) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3350)  at android.app.ActivityThread.access$1100(ActivityThread.java:222)  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1795)  at android.os.Handler.dispatchMessage(Handler.java:102)  at android.os.Looper.loop(Looper.java:158)  at android.app.ActivityThread.main(ActivityThread.java:7229)  at java.lang.reflect.Method.invoke(Native Method)

Answer 1

使用现有主键创建新 RealmObject 的正确方法是使用 realm.createObject(EmailRealmModel.class, emailID) 方法。

完整代码 fragment :

realm.beginTransaction();
EmailRealmModel email = realm.createObject(EmailRealmModel.class, emailID);
mailBoxRealmModel.getEmails().add(email);
realm.commitTransaction();

或者，如果您希望使用 inmemory 实例之一将更新存储在 Realm 对象中，您应该调用 realm.copyToRealmOrUpdate(obj)。

示例来自 documentation :

// For create managed proxy, you should wrap EmailRealmModel object by call copyToRealmXXX
EmailRealmModel email = realm.copyToRealmOrUpdate(new EmailRealmModel(id));
mailBoxRealmModel.getEmails().add(email);