EF Core 7: The INSERT statement conflicted with the foreign key constraint during SAVECHANGES

Question

I'm having a problem with inserting a parent and child as part of a single SaveChanges().

Below are my two tables:

Company {
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual Collection<User> Users { get; } = new List<User>();
}

User {
    public int Id { get; set; }
    public string FirstName { get; set; } = null!;
    public string LastName { get; set; } = null!;
    public string? Email { get; set; }
    public int CompanyId { get; set; }
    public virtual Company Company { get; set; } = null!
}

I'm using FluentApi to map the relationship:

builder.Entity<User>(entity =>
{
    entity.ToTable("users", "dbo");
    entity.HasOne(d => d.Company).WithMany(p => p.Users).HasForeignKey(d => d.CompanyId);
});

The code I used is:

var company = new Company()
{
    Name = "ABC"
}

_dbContext.Add(company);

var user = new User()
{
    FirstName = "John",
    LastName = "Smith",
    Email = "John.smith@gmail.com"
}
company.Users.Add(user);

_dbContext.Add(user);
_dbContext.SaveChanges();

When I call SaveChanges() I get an error:

SqlException: The INSERT statement conflicted with the FOREIGN KEY constraint "FK_Users_Companies_CompanyId". The conflict occurred in database "EFCore_Demo", table "dbo.Companies", column "Id".

The SQL being generated in the Output console is:

INSERT INTO dbo.Companies (Name)
OUTPUT INSERTED.Id
VALUES (@p0)

INSERT INTO dbo.Users (CompanyId, Email, FirstName, LastName)
OUTPUT INSERTED.Id
VALUES (@p1, @p2, @p3, @p4)

Thank you in advance.

Answer 1

I found the problem. I was not only adding the parent to the dbContext but also adding the children. As such, the children added alone do not have foreign keys, so the solution is to simply add your children to your parent object, and then ONLY "add" your parent to the dbContext.