How can I fetch list item and add to room database?

Question

Here is the code snippet in where Results data class contains list of objects:

@Entity(tableName = "objects_table")
data class Subscriber(

    @PrimaryKey(autoGenerate = true)
    @ColumnInfo(name = "object_id")
    var id: Int,
    @ColumnInfo(name = "object_name")
    var name: Results?,
    @ColumnInfo(name = "detected_time")
    var confidence: Results?

)

I tried Type converter but simililar error:

    @TypeConverter
fun restoreList(listOfString: String?): List<String?>? {
    return Gson().fromJson<List<String?>>(listOfString, object : TypeToken<List<String?>?>() {}.type)
}

@TypeConverter
fun saveList(listOfString: List<String?>?): String? {
    return Gson().toJson(listOfString)
}

The error is

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

Thanks in advance!

Does this answer your question? [Android room persistent library - TypeConverter error of error: Cannot figure out how to save field to database"](https://stackoverflow.com/questions/44582397/android-room-persistent-library-typeconverter-error-of-error-cannot-figure-ou) — Ryan M, Feb 25 '22 at 22:59

score 0 · Accepted Answer · answered Oct 19 '20 at 11:23

0

the type converter needed is type converter for the "Results" class not the String list you did

answered Oct 19 '20 at 11:23

Ramy Ibrahim

656
4
19

score 0 · Answer 2 · answered Oct 19 '20 at 11:51

Seems like you forgot to apply your TypeConverter class to your room database.

For example:

Database (note: you can have multiple TypeConverters)

@TypeConverters(
    value = [
        MyTypeConverters::class,
        MyOtherTypeConverters::class
    ]
) 
abstract class MyDatabase : RoomDatabase() {
    ...
}

TypeConverter

class MyTypeConverters {
    @TypeConverter
    fun restoreList(listOfString: String?): List<String?>? {
        return Gson().fromJson<List<String?>>(listOfString, object : TypeToken<List<String?>?>() {}.type)
    }

    @TypeConverter
    fun saveList(listOfString: List<String?>?): String? {
        return Gson().toJson(listOfString)
    }
}

score 0 · Answer 3 · answered Oct 19 '20 at 12:15

Add @Embedded annotation to your reference type variable.

Like that:

@Entity(tableName = "objects_table")
data class Subscriber(

    @PrimaryKey(autoGenerate = true)
    @ColumnInfo(name = "object_id")
    var id: Int,
    @Embedded(prefix = "name_")
    var name: Results?,
    @Embedded(prefix = "confidence_")
    var confidence: Results?
)

How can I fetch list item and add to room database?

3 Answers3