ASP.NET Core Web API working with Foreign Keys - api

Question

I'm developing Web Api operations for User Controller and I don't understand why I'm getting the error in the POST method :
The "PK_Section" of the PRIMARY KEY constraint was violated. Unable to insert duplicate key into dbo.Section object. Duplicate key value: (3fa85f64-5717-4562-b3fc-2c963f66afa4).
My IdentityUser model:
public string MiddleName { get; set; }
[Required]
public string Surname { get; set; }
public DateTime BirthDate { get; set; }
public string Address { get; set; }
[Required]
public string UserType { get; set; }
public bool ParentsAgreement { get; set; }
public Section BelongSection { get; set; }
Section Model:
[Required]
public Guid Id { get; set; }
public string Name { get; set; }
public string CoachName { get; set; }
public string SportComplexTitle { get; set; }
[IgnoreDataMember]
public ICollection<User> UsersList { get; set; }
DbContext:
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
//section
modelBuilder.Entity<User>()
.HasOne(s => s.BelongSection)
.WithMany(a => a.UsersList);
modelBuilder.Entity<Section>()
.HasMany(s => s.UsersList)
.WithOne(a => a.BelongSection);
}
And my POST Method:
[HttpPost]
public async Task<ActionResult<User>> Add(User user)
{
try
{
if (user == null)
{
return BadRequest();
}
myDbContext.Users.Add(user);
await myDbContext.SaveChangesAsync();
var result = await myDbContext.Users.Include(o => o.BelongSection).FirstOrDefaultAsync(o
=> o.Id == user.Id);
return result;
}
catch (Exception)
{
throw;
}
}
So, I'm getting the error, that I can't use the Id of the existing already Section in creating User.
My Post method body is:
{
"id": "3fa85f64-5717-4562-b3fc-2c963f66afa6",
"userName": "string",
"normalizedUserName": "string",
"email": "string",
"normalizedEmail": "string",
"emailConfirmed": true,
"passwordHash": "string",
"securityStamp": "string",
"concurrencyStamp": "string",
"phoneNumber": "string",
"phoneNumberConfirmed": true,
"twoFactorEnabled": true,
"lockoutEnd": "2021-04-15T08:31:12.271Z",
"lockoutEnabled": true,
"accessFailedCount": 0,
"name": "string",
"middleName": "string",
"surname": "string",
"birthDate": "2021-04-15T08:31:12.271Z",
"address": "string",
"userType": "string",
"parentsAgreement": true,
"belongSection": {
"id": "3fa85f64-5717-4562-b3fc-2c963f66afa4"
}
}

Answer 1

You could use two ways to add existing child to parent like below:
_context.Section.Attach(user.BelongSection);
Or:
_context.Entry(user.BelongSection).State = EntityState.Unchanged;
Be sure add AsNoTracking() to display the result.
Here is the whole working demo:
[HttpPost]
public async Task<ActionResult<User>> Add(User user)
{
try
{
if (user == null)
{
return BadRequest();
}
//_context.Section.Attach(user.BelongSection);
_context.Entry(user.BelongSection).State = EntityState.Unchanged;
_context.Users.Add(user);
await _context.SaveChangesAsync();
var result = await _context.Users.Include(o => o.BelongSection)
.AsNoTracking()
.FirstOrDefaultAsync(o=> o.Id == user.Id);
return result;
}
catch (Exception)
{
throw;
}
}
Note:
Not sure what is your asp.net core version, remember to add ReferenceLoopHandling.Ignore.
In asp.net core 3.x, System.Text.Json only supports serialization by value and throws an exception for circular references. So you need add Newtonsoft support like below:
services.AddControllers().AddNewtonsoftJson(options =>
{
options.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore;
});
In .Net 5.0,you could also add Newtonsoft support. Besides,System.Text.Json allows seting ReferenceHandler to Preserve:
https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json-preserve-references?pivots=dotnet-5-0