Insert entities one-to-many relation in Room Android

Question

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!

You can use type converters , see https://stackoverflow.com/a/51083865/6478047 — Manohar, Feb 12 '20 at 13:10

score 2 · Accepted Answer · answered Feb 12 '20 at 12:10

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
    }
}

Insert entities one-to-many relation in Room Android

1 Answers1