EF Core 不在子表中插入外键

Question

I have the following classes:

public class PresentingComplaintModel
{ 
    // for presenting complaints only
    [Key]
    public int ComplaintId { get; set; }
    public string Complaint { get; set; }
    public int? PatientId { get; set; }
    public Patient Patient { get; set; }
    public DateTime CreationDate { get; set; }
    public List<PatientComplaintQuestionAnswers> PatientComplaintQuestionAnswers { get; set; }
}

This class has a one-to-many relation to this class:

public class PatientComplaintQuestionAnswers
{ 
    [Key]
    public int Id { get; set; }
    public int? PresentingComplaintQuestionId { get; set; }
    public PresentingComplaintQuestionModel PresentingComplaintQuestionModel { get; set; }
    public bool Answer { get; set; }
    public int ComplaintId { get; set; } //from PresentingComplaintModel
    public PresentingComplaintModel PresentingComplaintModel {get;set;}
}

This class has two foreign keys: PresentingComplaintQuestionId and ComplaintId . The problem is when I insert a PresentingComplaintModel object into the database, the child table ( PatientComplaintQuestionAnswers ) receives data but the ComplaintId is always set to 0. Which means that the ComplaintId is not being populated from the primary key of the PresentingComplaintModel class.

I expect this to have non-zero primary key value. How to fix this problem?

PresentingComplaintModel is hydrated as follows. Here ComplaintId is always 0 as a new record is being created.

PresentingComplaintModel complaint = new();
List<PresentingComplaintQuestionModel> MasterQuestions { get; set; }
public PatientComplaintQuestionAnswers selectedItem1 { get; set; }

protected override async Task OnInitializedAsync()
{
    complaint.PatientComplaintQuestionAnswers = new List<PatientComplaintQuestionAnswers>();
    complaint.Complaint = "";
    complaint.CreationDate = DateTime.Now;
    complaint.PatientId = AppState.SelectedPatient.PatientId;
    MasterQuestions = await DataService.GetPresentingComplaintQuestionsAsync(); //get master questions.

    foreach (var q in MasterQuestions)
    {
        var ans = new PatientComplaintQuestionAnswers();
        ans.ComplaintId = complaint.ComplaintId;
        ans.PresentingComplaintQuestionId = q.PresentingComplaintQuestionId;
        ans.Answer = false;
        ans.PresentingComplaintQuestionModel = q;
        ans.PresentingComplaintModel = complaint; //reciprocal hydrating. see https://stackoverflow.com/questions/72293081/efcore-does-not-insert-foreign-key-in-child-table/72293303#72293303
        complaint.PatientComplaintQuestionAnswers.Add(ans);
    }
}

And then saved to DB:

var res = await DataService.UpdatePresentingComplaintAsync(complaint);
...
...
public async Task<bool> UpdatePresentingComplaintAsync(PresentingComplaintModel complaint)
{
    int res = 0;

    using (var scope = _scopeFactory.CreateScope())
    {
        var context = scope.ServiceProvider.GetRequiredService<ApplicationDbContext>();

        try
        {
            context.PresentingComplaints.Update(complaint);
            res = await context.SaveChangesAsync();
        }
        catch (Exception ex)
        {
        }
    }

    if (res > 0)
        return true;
    else
        return false;
}

And on the database side I see these insertions. Note that the ComplaintId column has all 0s in it:

Answer 1

Usually this is a lack of "reciprocal" hydrating.

public class MyParent()
{
    public MyParent()
    {
         this.TheKids = new List<MyChild>();
    }

    public long MyParentKey {get; set;} /* PK */


    public ICollection<MyChild> TheKids {get;set;}
}

public class MyChild()
{
  public long MyChildKey {get; set;} /* PK */
  public long MyParentKey {get;set;} /* FK to MyParent */

  public MyParent TheMyParent {get;set;} /* navigation property to MyParent */
}

When you hydrate "do not exist in the db yet" entities.. you gotta do some "reciprocal"

MyParent p1 = new MyParent();

MyChild c1 = new MyChild();

/* most people do this */
p1.TheKids.Add(c1);

/* the "reciprocal" that is sometimes missed */
c1.TheMyParent = p1;

(or it can be vice-versa, the child gets "TheMyParent" set, but the child is not added to the MyParent.TheKids collection)

Give that a try (make sure all reciprocals are set)

Note, I have NOT set MyChild.MyParentKey.

I would do it this way if the MyParent does not exist yet.

..

EF allows for a "short cut" of using FK scalars...IF they are known.

For example.

public class Employee()
{
  public long EmployeeKey {get; set;} /* PK */
  public string LastName {get; set;} 
  public string FirstName {get; set;} 
  public long ParentDepartmentKey {get;set;} /* FK to Department */

  public Department ParentDepartment {get;set;} /* navigation property to Department */
}

If I had the above class, and when I added a new Employee..and the Employee had to have its department set to an EXISTING department.

then I could do something like

Employee emp = new Employee();
emp.LastName = "Smith";
emp.FirstName = "Mary";

emp.ParentDepartmentKey = 333; /* an already existing Department */

This way, I do NOT have to fully hydrate the emp.ParentDepartment OBJECT (navigation property) to add the Employee.

So you need to be aware of "what exist and what does not yet exist" when populating your object-graph before giving it to your EF dbcontext and persisting the changes.

Answer 2

Ok, I found the fix. It seems that EFCore is not setting up the foreign key column properly in this case. So I modified the PatientComplaintQuestionAnswers class with explicit ForeignKey attributes:

public class PatientComplaintQuestionAnswers
{ 
    [Key]
    public int Id { get; set; }
    public int? PresentingComplaintQuestionId { get; set; }
    public PresentingComplaintQuestionModel PresentingComplaintQuestionModel { get; set; }
    public bool Answer { get; set; }
    public int ComplaintId { get; set; } //from PresentingComplaintModel
    public PresentingComplaintModel PresentingComplaintModel {get;set;}
}

To

public class PatientComplaintQuestionAnswers
    { //patient answers these questions in the patient presenting complaint form
        [Key]
        public int Id { get; set; }
        [ForeignKey("PresentingComplaintQuestionModel")]
        public int? PresentingComplaintQuestionId { get; set; }
        public PresentingComplaintQuestionModel PresentingComplaintQuestionModel { get; set; }
        public bool Answer { get; set; }
        [ForeignKey("PresentingComplaintModel")]
        public int ComplaintId { get; set; } //from PresentingComplaintModel
        public PresentingComplaintModel PresentingComplaintModel {get;set;}
    }

This fixed the relations and no extraneous columns were generated by EFCore either.