CODEWITHSUNDEEP
androidmvvmandroid-room
Sagar Balyan
Sagar Balyan

Reputation: 658

How to Save Foreign Keys in Room Database

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.

Upvotes: 0

Views: 87

Answers (1)

R&#243;bert Nagy
R&#243;bert Nagy

Reputation: 7700

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

Upvotes: 1

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