Asociar tablas usando la base de datos Room en Android Studio

Creo en el siguiente Ejemplo de trabajo es una de las formas en que puedes lograr lo que quieres.

El Código

La entidad del experimento (tabla) Experiment.java

@Entity
public class Experiment {

    @PrimaryKey(autoGenerate = true)
    private long experimentId;
    private String experimentName;
    private String experimentDate;

    public Experiment() {
    }

    @Ignore
    public Experiment(String name, String date) {
        this.experimentName = name;
        this.experimentDate = date;
    }

    public long getExperimentId() {
        return experimentId;
    }

    public void setExperimentId(long experimentId) {
        this.experimentId = experimentId;
    }

    public String getExperimentName() {
        return experimentName;
    }

    public void setExperimentName(String experimentName) {
        this.experimentName = experimentName;
    }

    public String getExperimentDate() {
        return experimentDate;
    }

    public void setExperimentDate(String experimentDate) {
        this.experimentDate = experimentDate;
    }
}

• Nada especial excepto quizás el @Ignorar 'd constructor (por conveniencia)

La entidad de prueba Trial.java

@Entity
public class Trial {

    @PrimaryKey(autoGenerate = true)
    private long trialId;
    @ForeignKey(entity = Experiment.class, parentColumns = {BaseColumns._ID},childColumns = "parentExperiment", onDelete = ForeignKey.CASCADE, onUpdate = ForeignKey.CASCADE)
    private long parentExperiment;
    private String trialVariable;
    private String trialResult;

    public Trial() {
    }

    @Ignore
    public Trial(long parentExperimentId, String variable, String result) {
        this.parentExperiment = parentExperimentId;
        this.trialVariable = variable;
        this.trialResult = result;
    }

    public long getTrialId() {
        return trialId;
    }

    public void setTrialId(long trialId) {
        this.trialId = trialId;
    }

    public long getParentExperiment() {
        return parentExperiment;
    }

    public void setParentExperiment(long parentExperiment) {
        this.parentExperiment = parentExperiment;
    }

    public String getTrialVariable() {
        return trialVariable;
    }

    public void setTrialVariable(String trialVariable) {
        this.trialVariable = trialVariable;
    }

    public String getTrialResult() {
        return trialResult;
    }

    public void setTrialResult(String trialResult) {
        this.trialResult = trialResult;
    }
}

• Nada especial excepto quizás el @Ignorar 'd constructor (por conveniencia)

Dao.java (combinado por conveniencia)

public interface Dao {

    @Insert(onConflict = OnConflictStrategy.IGNORE)
    long[] insertExperiments(Experiment... experiments);

    @Insert(onConflict = OnConflictStrategy.IGNORE)
    long insertExperiment(Experiment experiment);

    @Insert(onConflict = OnConflictStrategy.IGNORE)
    long[] insertTrials(Trial... trials);

    @Insert(onConflict = OnConflictStrategy.IGNORE)
    long insertTrial(Trial trial);

    @Update(onConflict = OnConflictStrategy.IGNORE)
    int updateExperiments(Experiment... experiments);

    @Update(onConflict = OnConflictStrategy.IGNORE)
    int updateExperiment(Experiment experiment);

    @Update(onConflict = OnConflictStrategy.IGNORE)
    int updateTrials(Trial... trials);

    @Update(onConflict = OnConflictStrategy.IGNORE)
    int updateTrial(Trial trial);

    @Delete
    int deleteExperiments(Experiment... experiments);

    @Delete
    int deleteExperiment(Experiment experiment);

    @Delete
    int deleteTrials(Trial... trials);

    @Delete
    int deleteTrial(Trial trial);

    @Query("SELECT * FROM Experiment")
    List<Experiment> getAllexperiments();

    @Query("SELECT * FROM Experiment WHERE experimentDate BETWEEN :startdate AND :enddate")
    List<Experiment> getExperimentsInDateRange(String startdate, String enddate);

    @Query("SELECT * FROM Trial")
    List<Trial> getAllTrials();

    @Query("SELECT * FROM Experiment JOIN Trial ON parentExperiment = experimentId")
    List<TrialWithExperiment> getExperimentsWithTrials();


    public class TrialWithExperiment {
        private long experimentId;
        private String experimentName;
        private String experimentDate;
        private long trialId;
        private String trialVariable;
        private String trialResult;

        public long getExperimentId() {
            return experimentId;
        }

        public void setExperimentId(long experimentId) {
            this.experimentId = experimentId;
        }

        public String getExperimentName() {
            return experimentName;
        }

        public void setExperimentName(String experimentName) {
            this.experimentName = experimentName;
        }

        public String getExperimentDate() {
            return experimentDate;
        }

        public void setExperimentDate(String experimentDate) {
            this.experimentDate = experimentDate;
        }

        public void setTrialId(long trialId) {
            this.trialId = trialId;
        }

        public long getTrialId() {
            return trialId;
        }

        public String getTrialVariable() {
            return trialVariable;
        }

        public void setTrialVariable(String trialVariable) {
            this.trialVariable = trialVariable;
        }

        public String getTrialResult() {
            return trialResult;
        }

        public void setTrialResult(String trialResult) {
            this.trialResult = trialResult;
        }
    }
}

• Tenga en cuenta el TrialWithExperiment clase, esto define una combinación de una Prueba y su Experimento.
• Observe cómo los nombres de las columnas son distintos, p. no solo id sino experimentId y ID de prueba los diferencia.
• Observe la última @Query getExperimentsWithTrials() esto devolverá una lista de Pruebas con sus experimentos.

@Database ExperimentDatabase.java

@Database(entities = {Experiment.class, Trial.class}, version = 1,exportSchema = false)
public abstract class ExperimentDatabase extends RoomDatabase {
    public abstract Dao getDao();
} 

Finalmente una actividad que utiliza lo anterior :-

public class MainActivity extends AppCompatActivity {

    ExperimentDatabase mDB;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mDB = Room.databaseBuilder(this,ExperimentDatabase.class,"experimentdb").allowMainThreadQueries().build();
        mDB.getDao().insertExperiments(new Experiment[]{
                new Experiment("Experiment 1","2019-01-01"),
                new Experiment("Experiment 2", "2019-02-01")
        });
        List<Experiment> experiments = mDB.getDao().getExperimentsInDateRange("2019-01-01","2019-12-31");
        for (Experiment e: experiments) {
            Log.d("EXPERIMENTS", "Experiment is " + e.getExperimentName() + " on " + e.getExperimentDate());
        }

        experiments = mDB.getDao().getAllexperiments();
        for (Experiment e: experiments) {
            Log.d("EXPERIMENTS", "Experiment is " + e.getExperimentName() + " on " + e.getExperimentDate());
        }

        for (Experiment e: experiments) {
            mDB.getDao().insertTrial(
                    new Trial(
                            e.getExperimentId(),
                            "Variable for " + e.getExperimentName(),
                            "Result for Experiment on " + e.getExperimentDate()
                    )
            );
        }

        List<Trial> trials = mDB.getDao().getAllTrials();
        for (Trial t: trials ) {
            Log.d("TRIAL ",
                    "Trial is for ExperimentID " + String.valueOf(t.getParentExperiment()) +
                            "\n\tVariable = " + t.getTrialVariable() +
                            "Result = " + t.getTrialResult()
            );
        }


        List<Dao.TrialWithExperiment> trialsWithExperiments = mDB.getDao().getExperimentsWithTrials();

        for (Dao.TrialWithExperiment te:trialsWithExperiments) {
            Log.d(
                    "TRIALWITHEXPERIMENT",
                    "Experiment Name = " + te.getExperimentName() +
                            "\n\tExperiment Date = " + te.getExperimentDate() +
                            "\n\t\tTrial Variable = " + te.getTrialVariable() +
                            "\n\t\tTrial Result = " + te.getTrialResult()
            );

        }
    }
}

Esto :-

• Agrega 2 experimentos (cada ejecución)
• Recupera experimentos en un intervalo de fechas (esto supone un formato de fecha reconocido por SQLite) y los envía al registro.
• Recupera todos los experimentos y los envía al registro.
• Utiliza la Lista de experimentos para agregar una Prueba a cada experimento.
• Recupera todas las Pruebas y las envía al registro.
• Recupera todos los ensayos junto con el experimento principal y los envía al registro.

El resultado

05-28 10:19:42.770 5750-5750/? D/EXPERIMENTS: Experiment is Experiment 1 on 2019-01-01
05-28 10:19:42.770 5750-5750/? D/EXPERIMENTS: Experiment is Experiment 2 on 2019-02-01
05-28 10:19:42.776 5750-5750/? D/EXPERIMENTS: Experiment is Experiment 1 on 2019-01-01
05-28 10:19:42.776 5750-5750/? D/EXPERIMENTS: Experiment is Experiment 2 on 2019-02-01
05-28 10:19:42.786 5750-5750/? D/TRIAL: Trial is for ExperimentID 1
      Variable = Variable for Experiment 1Result = Result for Experiment on 2019-01-01
05-28 10:19:42.786 5750-5750/? D/TRIAL: Trial is for ExperimentID 2
      Variable = Variable for Experiment 2Result = Result for Experiment on 2019-02-01
05-28 10:19:42.787 5750-5750/? D/TRIALWITHEXPERIMENT: Experiment Name = Experiment 1
      Experiment Date = 2019-01-01
          Trial Variable = Variable for Experiment 1
          Trial Result = Result for Experiment on 2019-01-01
05-28 10:19:42.787 5750-5750/? D/TRIALWITHEXPERIMENT: Experiment Name = Experiment 2
      Experiment Date = 2019-02-01
          Trial Variable = Variable for Experiment 2
          Trial Result = Result for Experiment on 2019-02-01

@Query("SELECT * FROM  Experiment")
List<ExperimentWithTrials> getExperimentsAndTrials();

class ExperimentWithTrials {
    private long experimentId;
    private String experimentName;
    private String experimentDate;
    @Relation(parentColumn = "experimentId", entityColumn = "parentExperiment")
    List<Trial> trials;

    public long getExperimentId() {
        return experimentId;
    }

    public void setExperimentId(long experimentId) {
        this.experimentId = experimentId;
    }

    public String getExperimentName() {
        return experimentName;
    }

    public void setExperimentName(String experimentName) {
        this.experimentName = experimentName;
    }

    public String getExperimentDate() {
        return experimentDate;
    }

    public void setExperimentDate(String experimentDate) {
        this.experimentDate = experimentDate;
    }

    public List<Trial> getTrials() {
        return trials;
    }

    public void setTrials(List<Trial> trials) {
        this.trials = trials;
    }
}

    List<Dao.ExperimentWithTrials> experimentsWithTrials = mDB.getDao().getExperimentsAndTrials();
    for (Dao.ExperimentWithTrials et: experimentsWithTrials ) {
        Log.d(
                "EXPERIMENTANDTRIALS",
                "Experiment Name = " + et.getExperimentName() +
                        "\n\tExperiment Date = " + et.getExperimentDate()
        );
        for (Trial t: et.getTrials()) {
            Log.d(
                    "TRIALFOREXPERIMENT",
                    "\t\tVariable = " + t.getTrialVariable() +
                            "\n\t\tResult = " + t.getTrialResult()
            );
        }
    }
}

05-28 13:05:35.052 6524-6524/? D/EXPERIMENTANDTRIALS: Experiment Name = Experiment 1
      Experiment Date = 2019-01-01
05-28 13:05:35.052 6524-6524/? D/TRIALFOREXPERIMENT:      Variable = Variable for Experiment 1
          Result = Result for Experiment on 2019-01-01
05-28 13:05:35.052 6524-6524/? D/EXPERIMENTANDTRIALS: Experiment Name = Experiment 2
      Experiment Date = 2019-02-01
05-28 13:05:35.052 6524-6524/? D/TRIALFOREXPERIMENT:      Variable = Variable for Experiment 2
          Result = Result for Experiment on 2019-02-01