Room field initialized at null

Question

I'm editing an existing entity of my project which looks like this (i added the sessionSettings field):

data class Patient(
    
    // ... other fields
    
    @Expose
    @SerializedName("exo_settings")
    @Embedded
    var exoSettingsData: ExoSettingsData? = null,   // already exist

    @Expose
    @SerializedName("session_settings")
    @TypeConverters(SessionSettingsConverters::class)
    var sessionSettings: SessionSettings? = null,   // the new field
    
    /// ... other fields

)

My TypeConverter class:

class SessionSettingsConverters {
    private var gson = Gson()

    @TypeConverter
    fun stringToSessionSettings(data: String?): SessionSettings? {
        if (data.isNullOrEmpty()) {
            return null
        }

        val sessionSettingsType = object : TypeToken<SessionSettings>() {}.type

        return gson.fromJson(data, sessionSettingsType)
    }

    @TypeConverter
    fun sessionSettingsToString(someObject: SessionSettings): String? {
        return gson.toJson(someObject)
    }
}

I added the sessionSettings; which is a basic object containing strings and integers, and it's TypeConverter to ease the integration. My issue is, i need this field to be null by default, because if it is, i'm grabbing data from another source. The problem is if I do so, my unit tests get broken if I do for exemple this:

val patient1 = Patient("1", synkStatus = SynkStatus.DELETED)
centerDatabase.patientDao().savePatient(patient1).test()

It fails (the entity is not saved), but if I initialize a SessionSettings object it works:

val patient1 = Patient("1", synkStatus = SynkStatus.DELETED, sessionSettings = SessionSettings())
centerDatabase.patientDao().savePatient(patient1).test()

So my question is: is there a way to allow saving this entity without initializing this field to keep it null by default ? Or the only way would be to add a boolean to track if this field as been edited or not ?

Thanks

Answer 1

The Issue Your issue appears to be that the TypeConverter will not accept a null when converting a SessionsSettings.

The Fix

Change to use someObject: SessionSettings? i.e. added the ?

Working Example/Demonstration

The following demonstrates the subtle change using code that is based upon your code i.e.:-

data class SessionSettings(
    val ssname: String,
    val ssine: Int
)

@Entity
data class Patient(
    @PrimaryKey
    val patientId: Long?=null,
    val patientName: String?=null,
    var sessionSettings: SessionSettings?,   // the new field
    /// ... other fields
)

class SessionSettingsConverters {
    private var gson = Gson()

    @TypeConverter
    fun stringToSessionSettings(data: String?): SessionSettings? {
        if (data.isNullOrEmpty()) {
            return null
        }
        val sessionSettingsType = object : TypeToken<SessionSettings>() {}.type
        return gson.fromJson(data, sessionSettingsType)
    }
    @TypeConverter
    fun sessionSettingsToString(someObject: SessionSettings?): String? {
        return gson.toJson(someObject)
    }
}

@Dao
interface SO75530351DAO {
    @Insert
    fun insert(patient: Patient): Long
    @Query("SELECT * FROM patient")
    fun getAllPatients(): List<Patient>
}

@TypeConverters(SessionSettingsConverters::class)
@Database(entities = [Patient::class], exportSchema = false, version = 1)
abstract class SO75530351DB: RoomDatabase() {
    abstract fun getDao(): SO75530351DAO
    companion object {
        private var instance: SO75530351DB?=null
        fun getInstance(context: Context): SO75530351DB {
            if (instance==null) {
                instance=Room.databaseBuilder(context,SO75530351DB::class.java,"so75539351.db")
                    .allowMainThreadQueries()
                    .build()
            }
            return instance as SO75530351DB
        }
    }
}

And to use the above:-

    dbx = SO75530351DB.getInstance(this)
    daox = dbx.getDao()

    daox.insert(Patient(patientName = "Fred"))
    daox.insert(Patient(patientName = "Mary", sessionSettings = SessionSettings("SESSION1",10)))
    for(p in daox.getAllPatients()) {
        Log.d("DBINFO","Patient is ${p.patientName} ID is ${p.patientId} ${p.sessionSettings}")
    }

The Log, after running:-

D/DBINFO: Patient is Fred ID is 1 null
D/DBINFO: Patient is Mary ID is 2 SessionSettings(ssname=SESSION1, ssine=10)

The database, via App Inspection, :-