必须用@NonNull (复合主键)注释主键

Question

我的Android项目中有以下Java类。

@Entity
public class Daily {

    @PrimaryKey
    private Date dailyId;

    //Other non important attrs, getters, setters, etc.

}

@Entity(primaryKeys = {"dailyId", "dailyDetailId"})
public class DailyDetail {

    private Date dailyId; //which is the value of its unique parent.
    private Long dailyDetailId;

    //Other non important attrs, getters, setters, etc.

}

顺便说一句:我已经添加了类型转换器。

当我试图构建这个项目时，我会得到以下错误：

You must annotate primary keys with @NonNull. "dailyId" is nullable. SQLite considers this a bug and Room does not allow it.

然后，当我按照说明将@NonNull添加到dailyid中时，它是Not-null fields must be initialized (?)

我该怎么解决这个问题？我的想法是初始化两个主键，但是当我尝试向DB插入一个新对象时，这应该是一个问题。

Answer 1

然后，当我按照指令将@NonNull添加到dailyid时，它说非空字段必须初始化(?)

如果用@NonNull对字段进行注释，就会告诉编译器“这个东西永远不会是空的”。但是，Java中未初始化对象的默认值是什么？没错!零。因此，如果用@NonNull对字段进行注释，则必须对其进行初始化，以确保它不会从null开始。

我该怎么解决这个问题？

初始化您的字段。无论是在声明时还是在类构造函数中。

@NonNull
@PrimaryKey
private Date dailyId = new Date(); // Now it's initialized and not null

或

@Entity
public class Daily {

    @NonNull
    @PrimaryKey
    private Date dailyId;

    public Daily() {
        dailyId = new Date(); // Now it's initialized and not null
    }

    // ^- this AND / OR this -v

    // Note here that if using an argument in the constructor, it too must be
    // annotated as @NonNull to tell the compiler that you're setting the value
    // of your non-nullable field to something that won't itself be null
    public Daily(@NonNull Date initialDate) {
        dailyId = initialDate; // Now it's initialized and not null
    }
}

希望这能帮上忙！