Question

如何查询另一个领域对象内的领域对象的大小

我有两个领域类Competition和User。 User是领域类，也包含在Competition中：

open class Competition (@PrimaryKey var competitionId: String?=null,
                      var user: User? =null): RealmObject()

open class User(@PrimaryKey var userId: String?=null,
                      var name: String? =null): RealmObject()

在某个时候，我想在竞赛中的特定CompetitionId中获得User的大小，而我对自己认为微不足道的问题却遇到了挑战

这是我尝试过的

var userObj = realm.where<Competition>().equalTo(
                "competitionId", competitionId
            ).findFirst().user.realm.where<User>().findAll().size

这给了我

kotlin.KotlinNullPointerException

Stacktrace：

2019-03-12 16:03:25.112 22028-22028/co.keepnet.bass W/System.err: kotlin.KotlinNullPointerException
2019-03-12 16:03:25.113 22028-22028/co.keepnet.bass W/System.err:     at co.keepnet.bass.ui.MainActivity$onClick$1.execute(MainActivity.kt:41)
2019-03-12 16:03:25.113 22028-22028/co.keepnet.bass W/System.err:     at io.realm.Realm.executeTransaction(Realm.java:1431)
2019-03-12 16:03:25.113 22028-22028/co.keepnet.bass W/System.err:     at co.keepnet.bass.ui.MainActivity.onClick(MainActivity.kt:37)
2019-03-12 16:03:25.113 22028-22028/co.keepnet.bass W/System.err:     at co.keepnet.bass.data.adapter.CompetitionsAdapter$onBindViewHolder$1.onClick(CompetitionsAdapter.kt:75)
2019-03-12 16:03:25.113 22028-22028/co.keepnet.bass W/System.err:     at android.view.View.performClick(View.java:6897)
2019-03-12 16:03:25.113 22028-22028/co.keepnet.bass W/System.err:     at android.view.View$PerformClick.run(View.java:26101)
2019-03-12 16:03:25.113 22028-22028/co.keepnet.bass W/System.err:     at android.os.Handler.handleCallback(Handler.java:789)
2019-03-12 16:03:25.113 22028-22028/co.keepnet.bass W/System.err:     at android.os.Handler.dispatchMessage(Handler.java:98)
2019-03-12 16:03:25.113 22028-22028/co.keepnet.bass W/System.err:     at android.os.Looper.loop(Looper.java:164)
2019-03-12 16:03:25.114 22028-22028/co.keepnet.bass W/System.err:     at android.app.ActivityThread.main(ActivityThread.java:6944)
2019-03-12 16:03:25.114 22028-22028/co.keepnet.bass W/System.err:     at java.lang.reflect.Method.invoke(Native Method)
2019-03-12 16:03:25.114 22028-22028/co.keepnet.bass W/System.err:     at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327)
2019-03-12 16:03:25.114 22028-22028/co.keepnet.bass W/System.err:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374)

Answer 1

我的意思是，相当琐碎，如果，您可以利用Realm的功能来发挥自己的优势（我认为3.5.0+）。

open class User(): RealmObject() {
    @PrimaryKey var userId: String? = null

    var name: String? = null

    @LinkingObjects("user")
    val userOfCompetitions: RealmResults<Competition>? = null
}

然后

val userCount = realm.where<User>()
                     .equalTo("userOfCompetitions.competitionId", competitionId)
                     .count()

查询领域类子对象的大小-Kotlin

1 个答案: