io.realm.exceptions.RealmMigrationNeededException：由于以下错误，需要迁移： - 添加了“SaveMessage”类

Question

我正在开发新应用，但出现以下异常

java.lang.RuntimeException：无法启动活动 组件信息{com.example.myapplication/com.example.myapplication.MessengerActivity}： io.realm.exceptions.RealmMigrationNeededException：迁移是 由于以下错误而需要： - 添加了“SaveMessage”类。 在 android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3102) 在 android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3237) 在 android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:81) 在 android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 在 android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 在 android.app.ActivityThread$H.handleMessage(ActivityThread.java:1929) 在 android.os.Handler.dispatchMessage(Handler.java:106) 在 android.os.Looper.loop(Looper.java:209) 在 android.app.ActivityThread.main(ActivityThread.java:7021) 在 java.lang.reflect.Method.invoke（本机方法） 在 com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:486) 在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:872) 引起：io.realm.exceptions.RealmMigrationNeededException：由于以下错误需要迁移： - 添加了“SaveMessage”类。 在 io.realm.internal.OsSharedRealm.nativeGetSharedRealm（本机方法） 在 io.realm.internal.OsSharedRealm.(OsSharedRealm.java:171) 在 io.realm.internal.OsSharedRealm.getInstance(OsSharedRealm.java:241) 在 io.realm.BaseRealm.(BaseRealm.java:136) 在 io.realm.BaseRealm.(BaseRealm.java:103) 在 io.realm.Realm.(Realm.java:163) 在 io.realm.Realm.createInstance(Realm.java:499) 在 io.realm.RealmCache.doCreateRealmOrGetFromCache(RealmCache.java:341) 在 io.realm.RealmCache.createRealmOrGetFromCache(RealmCache.java:284) 在 io.realm.Realm.getDefaultInstance(Realm.java:407) 在 com.example.myapplication.MessengerActivity.onCreate(MessengerActivity.java:92) 在 android.app.Activity.performCreate(Activity.java:7650) 在 android.app.Activity.performCreate(Activity.java:7639) 在 android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1295) 在 android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3077)

下面是我的代码：

Realm.init(this);
        realm = Realm.getDefaultInstance();
        realm.beginTransaction();

        User userModel =  realm.createObject(User.class);


        Integer userId = Integer.valueOf("0");
        String userName = "Michael";

        userModel.setId(userId);
        userModel.setName(userName);
        //userModel.setIcon("icon");
        Integer userId1 = Integer.valueOf("1");
        String userName1 = "Lily";



        userModel.setId(userId1);
        userModel.setName(userName1);


        realm.commitTransaction();


        RealmResults<User> userModels = realm.where(User.class).findAll();
        for (User user : userModels) {
            Integer getId = Integer.valueOf(user.getId());
            String getName = user.getName();
            realm.commitTransaction();

        }

        SaveMessage saveModel = realm.createObject(SaveMessage.class);


       Integer saveId = Integer.valueOf("0");
       String savedName = "Michael";
        Integer saveIds = Integer.valueOf("1");
        String savedNames = "Lily";
        saveModel.setmId(saveId);
        saveModel.setmUsername(savedName);
        saveModel.setmContent("content");
        saveModel.ismRightMessage("isRightMessage");
        Date now = Calendar.getInstance().getTime();
        saveModel.setDate(now);
        realm.commitTransaction();



        RealmResults<SaveMessage> savesModels = realm.where(SaveMessage.class).findAll();
        for (SaveMessage saveMessage : savesModels) {
            Integer getId = saveMessage.getId();
            String getName = saveMessage.getUsername();
            String getContent = saveMessage.getContent();
            Date date = saveMessage.getDate();
            String rightMessage = String.valueOf(saveMessage.ismRightMessage());

            realm.commitTransaction();

        }

我的 SaveMessage 模型类：

@RealmClass
public class SaveMessage extends RealmObject {


    private int mId;
    private String mUsername;
    private String mContent;
    private Date mCreatedAt;
    private boolean mRightMessage;
    private String mPictureString;
    private String mType;

    public SaveMessage(int id, String username, String content, Date createdAt, boolean isRightMessage) {
        mId = id;
        mUsername = username;
        mContent = content;
        mCreatedAt = createdAt;
        mRightMessage = isRightMessage;
    }

    public SaveMessage() {

    }

    public int getId() {
        return mId;
    }

    public String getUsername() {
        return mUsername;
    }

    public String getContent() {
        return mContent;
    }

    public Date getDate() {
        return mCreatedAt;
    }

    public void setDate(Date createdAt) {


        mCreatedAt = createdAt;
    }




    public boolean ismRightMessage() {
        return mRightMessage;
    }

    public int getmId() {
        return mId;
    }

    public void setmId(int mId) {
        this.mId = mId;
    }

    public String getmUsername() {
        return mUsername;
    }

    public void setmUsername(String mUsername) {
        this.mUsername = mUsername;
    }

    public String getmContent() {
        return mContent;
    }

    public void setmContent(String mContent) {
        this.mContent = mContent;
    }


    public boolean ismRightMessage(String isRightMessage) {
        return mRightMessage;
    }

    public void setmRightMessage(boolean mRightMessage) {
        this.mRightMessage = mRightMessage;
    }

    public String getPictureString() {
        return mPictureString;
    }

    public void setPictureString(String pictureString) {
        mPictureString = pictureString;
    }

    public String getType() {
        return mType;
    }

    public void setType(String type) {
        mType = type;
    }



}

Answer 1

您在领域架构中添加了一个新模型，因此您需要迁移您的数据库。你可以这样做：

  public class RealmUtility {
       private static final int SCHEMA_V_PREV = 1;// previous schema version
        private static final int SCHEMA_V_NOW = 2;// change schema version if any change happened in schema


        public static int getSchemaVNow() {
            return SCHEMA_V_NOW;
        }


        public static RealmConfiguration getDefaultConfig() {
            return new RealmConfiguration.Builder()
                    .schemaVersion(SCHEMA_V_NOW)
                    .deleteRealmIfMigrationNeeded()// if migration needed then this methoud will remove the existing database and will create new database
                    .build();
        }
}

如果您不想删除现有数据库并愿意在现有数据库中添加新模型，请这样做：

  public class RealmMigrations implements RealmMigration {

        @Override
        public void migrate(DynamicRealm realm, long oldVersion, long newVersion) {
            final RealmSchema schema = realm.getSchema();

            if (oldVersion == 1) {
                final RealmObjectSchema saveMessage = 
                     schema.get("SaveMessage");
                      if(saveMessage==null){
                      saveMessage=realmSchema.create("SaveMessage");}
                      saveMessage.addField("mId", int.class);
                   // all field add here similarly
                         oldVersion++;
            }
        }
    }

    public static RealmConfiguration getDefaultConfig() {
            return new RealmConfiguration.Builder()
                    .schemaVersion(SCHEMA_V_NOW)
                     .migration(new RealmMigrations())               
                    .build();
        }

然后像这样初始化领域：

Realm realm = Realm.getInstance(RealmUtility.getDefaultConfig());

Answer 2

在领域迁移期间，我收到以下错误：-

java.lang.RuntimeException: Unable to create application com.merqueo.app.AppController: io.realm.exceptions.RealmMigrationNeededException: Migration is required due to the following errors:

Property 'User.departmentId' has been made optional.
Property 'User.taskId' has been made optional.

原因是模型有一个可为空的字段，但迁移向 DB 添加了一个不可为空的字段。

解决方案第一：-

String::class.javaObjectType which will give you the wrapper class

第二个：-

realm.schema.get("Class")?.apply {
    addField("departmentId", String::class.java).setNullable("departmentId", true)
    addField("taskId", String::class.java).setNullable("taskId", true)
}