Android Realm处理关系对象中的主键 [英] Android Realm Handling Primary Key in Relational Object
问题描述
我有两个对象:MailBox
和Email
.每个接收方都有许多Emails
.
I have two objects: MailBox
and Email
. Each Receiver has many 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;
}
将电子邮件添加到MailBoxRealmModel时如何使用**realm.insertOrUpdate**
?
How can one use **realm.insertOrUpdate**
when adding email to MailBoxRealmModel?
EmailRealmModel email = new EmailRealmModel();
email.setMessageId(emailID);
realm.insertOrUpdate(email );
mailBoxRealmModel.getEmails().add(email);
我在此行上得到一个空指针异常email
:
I am getting a null pointer exception email
on this line:
mailBoxRealmModel.getEmails().add(email);
例外:
原因:java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法"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) 在java.lang.reflect.Method.invoke(本机方法)
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)
推荐答案
使用现有主键创建新RealmObject的正确方法是用法realm.createObject(EmailRealmModel.class, emailID)
方法.
Proper way to create a new RealmObject with existing primary key is usage realm.createObject(EmailRealmModel.class, emailID)
method.
完整代码片段:
realm.beginTransaction();
EmailRealmModel email = realm.createObject(EmailRealmModel.class, emailID);
mailBoxRealmModel.getEmails().add(email);
realm.commitTransaction();
或者,如果您希望使用一个内存实例之一将更新存储在领域对象中,则应调用realm.copyToRealmOrUpdate(obj)
.
Or, if you wish update stored in realm object using one of inmemory instances, you should call realm.copyToRealmOrUpdate(obj)
.
// For create managed proxy, you should wrap EmailRealmModel object by call copyToRealmXXX
EmailRealmModel email = realm.copyToRealmOrUpdate(new EmailRealmModel(id));
mailBoxRealmModel.getEmails().add(email);
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