How to Save Foreign Keys in Room Database

Question

I have the following Model class that i want to store in Room Database:

I don't know much but i think i need to use foreign key here. Though i dont have much idea, its just a guess.

If you can give a detailed explanation,

 public class EarthquakeData { public List < Feature > features; public class Feature { public String type; public Properties properties; // public Geometry geometry; public String id; public class Properties { public double mag; public String place; public Object time; public Object updated; public Object tz; public String url; public String detail; public int felt; public double cdi; public double mmi; public String alert; public String status; public int tsunami; public int sig; public String net; public String code; public String ids; public String sources; public String types; public int nst; public double dmin; public double rms; public double gap; public String magType; public String type; public String title; } } }

I have saved only a simple class in Room database like the following class:

 @Entity(tableName = "notes") public class Note { @PrimaryKey @NonNull private String id; @NonNull @ColumnInfo(name = "note") private String mNote; public Note(@NonNull String id, @NonNull String mNote) { this.id = id; this.mNote = mNote; } @NonNull public String getId() { return id; } @NonNull public String getNote() { return this.mNote; } }

But i don't know to save the first type of model class in Room which is very complex for me because it consists of objects within a class.

Answer 1

From what I understand you have the following relationships:

1 EarthquakeData - Many Features
and
1 Feature - 1 Properties

So you could model it this way:

Table Features(id: PrimaryKey, earthquake_data_id: ForeignKey, ...)

and Table Feature(id: PrimaryKey, properties_id: ForeignKey, ...)

With Room entities this would look something like this for the features:

@Entity(
    tableName = "features",
    foreignKeys = [
        ForeignKey(
            entity = EarthquakeDataEntity::class,
            parentColumns = ["id"],
            childColumns = ["earthquake_data_id"],
            onDelete = ForeignKey.CASCADE, // See documentation for other operations
            onUpdate = ForeignKey.CASCADE
        )
    ]
class Features {
    ...
}

Check out the ForeignKey official documentation for the parameters