如何将Room TypeConverter应用于实体的单个字段? [英] How to apply Room TypeConverter to a single field of an entity?

问题描述

我一直在尝试将TypeConverter应用于Room数据库实体的单个字段的不同解决方案，但出现错误

I have been trying different solutions for applying a TypeConverter to a single field of a Room database entity but I am getting an error

Cannot figure out how to save this field into database. You can consider adding a type converter for it.

当我将转换器应用于这样的实体时:

When I apply the converter to the entity like this:

@Entity(tableName = DBKey.calendarDayTable)
@TypeConverters(DateStringConverter::class)
data class CalendarDay(

    @PrimaryKey
    val date: Date
)

一切正常，但是当我将其应用于这样的领域时:

everything works as expected, but when I apply it to the field like this:

@Entity(tableName = DBKey.calendarDayTable)
data class CalendarDay(

    @PrimaryKey
    @TypeConverters(DateStringConverter::class)
    val date: Date
)

我收到上述错误.

DateStringConverter类为:

class DateStringConverter {
    private val formatter = SimpleDateFormat("yyyy-MM-dd")

    @TypeConverter
    fun dateFromString(value: String): Date {
        return formatter.parse(value)!!
    }

    @TypeConverter
    fun dateToString(date: Date): String {
        return formatter.format(date)
    }
}

我正在使用Room版本2.2.5，并用Kotlin编写应用程序. Room的依赖项为:

I am using the Room version 2.2.5 and writing the app in Kotlin. The dependencies for Room are:

implementation "androidx.room:room-runtime:$room_version"
kapt "androidx.room:room-compiler:$room_version"
implementation "androidx.room:room-ktx:$room_version"

是否可以仅将DateStringConverter应用于CalendarDay实体的date字段，还是必须将其应用于整个实体?

Is there a way that I can apply DateStringConverter only to the date field of the CalendarDay entity, or do I have to apply it to the whole entity?

推荐答案

您必须指定将注释应用于字段

You must specify that the annotation should be applied to the field

@field:TypeConverters(DateStringConverter::class)
val date: Date

如果未指定使用场所目标，则根据所使用注释的@Target注释选择目标.如果有多个适用目标，则使用以下列表中的第一个适用目标:

If you don't specify a use-site target, the target is chosen according to the @Target annotation of the annotation being used. If there are multiple applicable targets, the first applicable target from the following list is used:

• param(构造函数参数)；
• 财产；
• 字段.

• param (constructor parameter);
• property;
• field.

https://kotlinlang.org/docs/reference /annotations.html#annotation-use-site-targets

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