问询RealmList的remove方法作用：User与Task 1:N关联场景

Great question—this is a frequent point of confusion when working with Realm's relational models! Let's break it down clearly:

When you call remove() on a managed RealmList (like the one returned by RealmUser.getTasks()), it only breaks the relationship/link between the RealmUser and the specific RealmTask object—it does not delete the RealmTask itself from the Realm database.

Why is that? #

Realm's 1:N relationships are reference-based. A single RealmTask could potentially be linked to other objects (even in your 1:N setup, it might exist independently in the database without any parent references). Realm doesn't assume you want to delete the child object just because you remove it from a parent's list.

Example to clarify the difference #

// Get a managed RealmUser and its tasks
RealmUser managedUser = realm.where(RealmUser.class)
    .equalTo("id", targetUserId)
    .findFirst();

// Grab a task from the user's list
RealmTask taskToModify = managedUser.getTasks().get(0);

// 1. This only removes the task from the user's RealmList—task still exists in Realm
managedUser.getTasks().remove(taskToModify);

// 2. This actually deletes the task from the Realm database entirely
taskToModify.deleteFromRealm();

If you want to delete child objects when removing them from the list #

If your use case requires deleting the RealmTask when it's removed from the user's list, you'll need to do this explicitly in a Realm transaction:

realm.executeTransaction(r -> {
    RealmTask taskToDelete = managedUser.getTasks().get(0);
    managedUser.getTasks().remove(taskToDelete);
    taskToDelete.deleteFromRealm();
});

Alternatively, if you want child objects to be automatically deleted when the parent is deleted (cascade delete), you can use Realm's @CascadeOnDelete annotation (available in Realm Java 5.0 and later) on your RealmList field:

public class RealmUser extends RealmObject {
    // ... other fields
    @CascadeOnDelete
    private RealmList<RealmTask> tasks;
    // ... getters/setters
}

内容的提问来源于stack exchange，提问作者elnino