How To Save Enum Field In The Database Room?

I must write the value from the enum enumeration to the database. An error occurs during compilation. What am I doing wrong? Cannot figure out how to save this field into database

Solution 1:

You can make a convert to each enum, like this:

classConverters{

     @TypeConverterfuntoHealth(value: String) = enumValueOf<Health>(value)

     @TypeConverterfunfromHealth(value: Health) = value.name
}

Or if you prefer store it as SQL integer, you can use ordinal too:

classConverters{

    @TypeConverterfuntoHealth(value: Int) = enumValues<Health>()[value]

    @TypeConverterfunfromHealth(value: Health) = value.ordinal
}

Unfortunatally, there is no way to use generics Enum<T> to accomplish this since unbound generics will raise an error Cannot use unbound generics in Type Converters.

Android Room team could seriously add an annotation and a generator for Enums to their kapt compiler.

Finally, annotate a database class, entity class, dao class, dao method, dao method parameter or entity field class with this:

@TypeConverters(Converters::class)

Solution 2:

To fix this annotate your Database class with @TypeConverters annotation (and not your enum class).

Example:

@Database(entities = arrayOf(User::class), version = 1)
@TypeConverters(Converters::class)abstractclassAppDatabase : RoomDatabase() {
    abstractfunuserDao(): UserDao
}

Check https://developer.android.com/training/data-storage/room/referencing-data

Solution 3:

This is no longer an issue in version 2.3.0-alpha4: "Room will now default to using an Enum to String and vice versa type converter if none is provided. If a type converter for an enum already exists, Room will prioritize using it over the default one."

"If a one-way type converter for reading already exists for the Enum, Room might accidentally use the built-in String to Enum converter which might not be desired. This is a known issue and can be fixed by making it a two-way converter."

Solution 4:

Enum class;

enumclassPriority {
HIGH,
MEDIUM,
LOW
}

Converter class;

classConverter{

@TypeConverterfunfromPriority(priority: Priority): String {
    return priority.name
}

@TypeConverterfuntoPriority(priority: String): Priority {
    return Priority.valueOf(priority)
}

}

usage;

@Database(entities = [MyData::class], version = 1, exportSchema = false)
@TypeConverters(Converter::class)
abstract class MyDatabase : RoomDatabase() {

  // todo

}

Solution 5:

For java developers

The Enum

publicenumHealth {
    NONE(-1),
    VERY_BAD(0);

    publicfinalint value;

    Health(int newValue) {
        value = newValue;
    }

    publicintgetValue(){
        return value;
    }
}

The type converter

publicclassHealthConverter {

    /**
     * Convert Health to an integer
     */
    @TypeConverter
    publicstaticintfromHealthToInt(Health value){
        return value.ordinal();
    }

    /**
     * Convert an integer to Health
     */
    @TypeConverter
    publicstatic Health fromIntToHealth(int value){
        return (Health.values()[value]);
    }

}