Question

我有两个对象：MailBox和Email。每个接收器都有许多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);

我在这一行得到一个空指针异常email：

mailBoxRealmModel.getEmails().add(email);

例外：

引起：java.lang.NullPointerException：尝试在空对象引用上调用虚方法'boolean io.realm.RealmList.add（io.realm.RealmModel）' 在com.koa.mailbox.MailBoxActivity $ 1.execute（MailBoxActivity.java:123）在io.realm.Realm.executeTransaction（Realm.java:1253）在com.koa.mailbox.MailBoxActivity.test（MailBoxActivity.java:88）在com.koa.mailbox.MailBoxActivity.onCreate（MailBoxActivity.java:71）在android.app.Activity.performCreate（Activity.java:6876）在android.app.Instrumentation.callActivityOnCreate（Instrumentation.java:1135）在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:3207）在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:3350）在android.app.ActivityThread.access $ 1100（ActivityThread.java:222）在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1795）在android.os.Handler.dispatchMessage（Handler.java:102）在android.os.Looper.loop（Looper.java:158）在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。

完整代码片段：

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

或者，如果您希望使用其中一个内存实例存储在realm对象中的更新，则应调用realm.copyToRealmOrUpdate(obj)。

来自documentation的示例：

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

Answer 2

在非托管的RealmObject上，必须手动初始化RealmList字段。

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

mailBoxRealmModel.setEmails(new RealmList<MailBoxRealmModel>());
mailBoxRealmModel.getEmails().add(email);
realm.insertOrUpdate(mailBoxRealmModel);

Android领域处理关系对象中的主键

2 个答案: