實體框架6中的多重關係變化從1對多到1對0或0..1

Question

我正在與具有1對多關係的兩個實體County和Patient一起工作。

public class County 
{ 
    public int CountyId { get; set; } // Primary Key 
    public string CountyName { get; set;) // A unique index column 
    public virtual ICollection<Patient> Patients { get; set; } 
} 

public class CountyMap : EntityTypeConfiguration<County> 
{ 
    public CountyMap() 
    { 
     ToTable("Counties"); 
     HasKey(c => c.CountyId); 
     Property(c => c.CountyId).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity); 
      Property(c => c.CountyName).IsRequired().HasMaxLength(50).HasColumnAnnotation("Index", 
       new IndexAnnotation(new IndexAttribute("IX_Counties", 1) { IsUnique = true })); 
    } 
} 

public class Patient 
{ 
    public int PatientId { get; set; } 
    public string PatientLastName { get; set; } 
    public string PatientFirstName { get; set; } 
    public string CountyName { get; set; } 
    public int CountyId { get; set; } // Foreign key to Counties table 
    public virtual County County { get; set; } // Navigation property 
} 

public class PatientMap: EntityTypeConfiguration<Patient> 
{ 
    public PatientMap() 
    { 
      ToTable("Patients"); 
      HasKey(p => p.PatientId); 
      Property(p => p.PatientId).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity); 
      Property(p => p.PatientLastName).IsRequired().HasMaxLength(50); 
      Property(p => p.PatientFirstName).IsRequired().HasMaxLength(50); 
      Property(p => p.CountyId).IsRequired(); 
      HasRequired(p => p.County).WithMany(c => c.Patients).HasForeignKey(p => p.CountyId); 
    } 
} 

public class AppContext : DbContext 
{ 
    public AppContext() 
     : base("name=AppContext") 
    { 
    } 

    public virtual DbSet<County> Counties { get; set; } 
    public virtual DbSet<Patient> Patients { get; set; } 

    protected override void OnModelCreating(DbModelBuilder modelBuilder) 
    { 
     modelBuilder.Configurations.Add(new CountyMap()); 
     modelBuilder.Configurations.Add(new PatientMap()); 
    } 
} 

public class PatientUOW 
{ 
    public Patient CreatePatient(Patient patient) 
    { 
     string errorMessage = String.Empty; 
     Patient patientReturned = null; 
     County county = null; 

     try 
     { 
      using (AppContext ctx = new AppContext()) 
      { 
       // ONLY Pre-existing counties are permitted 
       county = ctx.Counties.Where(c => c.CountyName == patient.CountyName).SingleOrDefault<County>(); 

       county.Patients.Add(patient); 
       ctx.SaveChanges(); // An exception is thrown here 

      } 
     } 
     catch (Exception err) 
     { 
     } 
    } 
} 

異常消息是：

多重約束侵犯。 角色'Patient_County_Target'的關係'ArielOperations.Domain.Concrete.Patient_County'具有 多重性1或0..1。

在縣實體的調試器顯示：

和

誰能解釋這裏發生了什麼？我在這裏和其他地方看到了幾個條目，而且沒有一條似乎有效。

謝謝。

Answer 1

我能解決我的問題。關鍵似乎是爲了避免在縣中添加患者時嘗試創建新的縣記錄。爲了實現這一點，我沒有將County實例傳遞給CreatePatient方法。新患者只包含目標縣的CountyId。

Patient newPatient = new Patient 
{ 
    PatientLastName = "Doe", 
    PatientFirstName = "Jane", 
    CountyName = "Denton", 
    CountyId = 4 
}; 

我們可以在這個newPatient實例現在傳遞給CreatePatient方法。

public Patient CreatePatient(Patient patient) 
{ 
    string errorMessage = String.Empty; 
    Patient patientReturned = null; 
    County county = null; 

    try 
    { 
      using (AppContext ctx = new AppContext()) 
      { 
       // ONLY Pre-existing counties are permitted 
       county = ctx.Counties.Where(c => c.CountyName == patient.CountyName).SingleOrDefault<County>(); 
       ctx.Patients.Add(patient); 
       ctx.SaveChanges(); 
       patientReturned = patient; 
      } 
    } // end try 
    catch (Exception err) 
    { 
     errorMessage = err.Message; 
    } // end catch (Exception err) 

    return patientReturned; 
} // end public Patient CreatePatient(Patient patient) 

這似乎工作，甚至通過外鍵將患者連接到縣記錄。看來EF在這裏做了一些事情來達到預期目的。