“需要领域迁移"，android中的异常，同时从领域db检索值 [英] "realm migration needed", exception in android while retrieving values from realm db

问题描述

我在应用程序中使用Realm作为后端.我创建了一个名为Setting的表.我按照Realm官方网站上给出的步骤在该表中添加了值. 但是，当我要从该表中检索值时，出现异常

I am using Realm as a back end in my application. I have created one table named Setting. I added values in that table, by following the steps given on Realm's official site. But when I am going to retrieve values from that table in, I getting exception

"io.realm.exceptions.RealmMigrationNeededException:必须提供RealmMigration":"realm = Realm.getInstance(getApplicationContext());".

"io.realm.exceptions.RealmMigrationNeededException: RealmMigration must be provided" on the line:" realm=Realm.getInstance(getApplicationContext());".

实际上，我是android和Realm的新手，所以很难理解问题所在.

Actually, I am new to android and Realm, so finding trouble to understand what is problem.

推荐答案

对于Realm的新版本，添加了Realm.init(上下文上下文)

for new versions of Realm, Realm.init(Context context) is added

Realm.init(context);    
RealmConfiguration config = new RealmConfiguration
                                     .Builder()
                                     .deleteRealmIfMigrationNeeded()
                                     .build();

注意:使用此配置选项，任何架构更改都会导致 数据丢失，特别是:

NOTE: With this config option, any schema change will result in loss of data, specifically:

• 添加/删除字段
• 添加了一个新的RealmObject类
• 现有RealmObject被删除
• @Required已添加/删除
• @PrimaryKey已添加/删除
• @Index已添加/删除

• a field is added/removed
• a new RealmObject class is added
• an existing RealmObject is removed
• @Required is added/removed
• @PrimaryKey is added/removed
• @Index is added/removed

因此，主要建议在应用处于开发阶段时使用.

So it's primarily recommended while the app is in the development stage.

或在官方文档之后添加迁移:

Or add a migration following the official docs:

https://realm.io/docs/java/latest/#migrations

例如

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

        if (oldVersion == 0) {
            RealmObjectSchema personSchema = schema.get("Person");
            personSchema
                .addField("fullName", String.class, FieldAttribute.REQUIRED);
            oldVersion++;
            ... 

  // hash code, equals 

还有

Realm.init(context);    
RealmConfiguration config = new RealmConfiguration.Builder() 
                                 .migration(new Migration()) 
                           //      .deleteRealmIfMigrationNeeded()
                                 .build();

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