Insert entities one-to-many relation in Room Android

Hanna :

Help please! I have a problem only with insert pojos in databes with relation one-to-many. I have pojos and misunderstood how insert all list in database???

@Entity
data class Street(
    @PrimaryKey(autoGenerate = true)
    var id: Int = 0
) {
    @Ignore
    var houses: List<House>? = listOf()
}

@Entity
data class House(
    @PrimaryKey(autoGenerate = true)
    var id: Int = 0,
    var streetId: Int
) {
    @Ignore
    var flats: List<Flat>? = listOf()
}

@Entity
data class Flat(
    @PrimaryKey(autoGenerate = true)
    var id: Int = 0,
    var houseId: Int
)

Please help me guys!

Alex Grebennikov :

You need to remove @Ignore annotations and use type converters.

IMHO it is better to save only the ids of the pojo and not the whole object e.g.

@Entity
data class House(
    @PrimaryKey(autoGenerate = true)
    var id: Int = 0,
    var streetId: Int,
    var flatIds: List<Int>? = listOf()
)

And when you need all those flats just query the FlatDao by those ids

---

If you still want to save whole object you can convert it to Gson and then convert back

class YourObjectConverter {

    @TypeConverter
    fun listToJson(value: List<YourObject>?): String {

        return Gson().toJson(value)
    }

    @TypeConverter
    fun jsonToList(value: String): List<YourObject>? {

        val objects = Gson().fromJson(value, List<YourObject>::class.java) as Array<YourObject>
        val list = objects.toList()
        return list
    }
}