Dapper returning zero GUID

Question

Dapper constantly returns the default value instead of the ID. What could be the problem and how to fix it? (Dapper + PostgreSQL)

Can you explain to me what is the problem?

public async Task<Appointment?> GetByIdWithPatientAndDoctorAsync(Guid id)
{
    await using var connection = new NpgsqlConnection(connectionString);
    await connection.OpenAsync();
    const string query = """
                             select a.*, 
                                    p.*, 
                                    d.*, 
                                    c.*, 
                                    s.name as specializationname
                             from 
                                 appointments a
                             inner join 
                                 patients p on a.patientid = p.id
                             inner join 
                                 doctors d on a.doctorid = d.id
                             inner join 
                                 clinics c on a.clinicid = c.id
                             inner join 
                                 specializations s on d.specializationid = s.id
                             where 
                                 a.id = @Id
                         """;

    var appointments = await connection.QueryAsync<Appointment, Patient, Doctor, Clinic, Specialization, Appointment>(
        query,
        (appointment, patient, doctor, clinic, specialization) =>
        {
            appointment.Patient = patient;
            doctor.Specialization = specialization;
            appointment.Doctor = doctor;
            appointment.Clinic = clinic;
            return appointment;
        },
        new { Id = id },
        splitOn: "id, id, id, specializationname");

    return appointments.FirstOrDefault();
}

public class Appointment : Entity
{
    public Appointment() {}
    public Appointment(DateTime date, Guid patientId, Guid doctorId, Guid clinicId, AppointmentStatus appointmentStatus)
    {
        Date = date;
        PatientId = patientId;
        DoctorId = doctorId;
        ClinicId = clinicId;
        AppointmentStatus = appointmentStatus;
    }

    public DateTime Date { get; set; }
    public Guid PatientId { get; set; }
    public Patient Patient { get; set; }
    public Guid DoctorId { get; set; }
    public Doctor Doctor { get; set; }
    public Guid ClinicId { get; set; }
    public Clinic Clinic { get; set; }
    public AppointmentStatus AppointmentStatus { get; set; }
}

public abstract class Entity
{
    protected Entity() {}

    protected Entity(Guid id)
    {
        Id = id;
    }
    
    public Guid Id { get; }
}

I've already tried playing with splitOn and leading through as ID to another name and nothing helped.

Answer 1

As mentioned in the comment, in the Entity class the Id property doesn't contain a setter. Thus it is not assigned with value, as default it is Guid.Empty.

Add setter should resolve the problem.

public abstract class Entity
{
    protected Entity() {}

    protected Entity(Guid id)
    {
        Id = id;
    }
    
    public Guid Id { get; set; }
}