The INSERT statement conflicted with the FOREIGN KEY constraint - entity-framework

Question

I'm rather new to Entity Framework (code-first). Here are my two entities-
public class Employee
{
public Employee() { }
public long Id {get; set;}
public string Fullname {get; set;}
public virtual ICollection<Attendance> Attendances { get; set; }
}
public class Attendance
{
public Attendance() { }
public DateTime CheckinDateTime { get; set; }
public DateTime? CheckoutDateTime { get; set; }
public long EmployeeId { get; set; }
[ForeignKey("Id")]
public virtual Employee Employee{ get; set; }
}
Employee has one-to-many relation with Attendance.
I've tried to create a new Attendance data-
var attendance = new Attendance()
{ EmployeeId = 1,
CheckinDateTime = today.CurrentDateTime
};
DbContext.Attendances.Add(attendance);
DbContext.SaveChanges(); //Exception here.
I have an Employee record in database.
Why I'm getting the exception?

Answer 1

Code First enables you to describe a model by using C# or Visual Basic .NET classes. The basic shape of the model is detected by using conventions. Conventions are sets of rules that are used to automatically configure a conceptual model based on class definitions when working with Code First. The conventions are defined in the System.Data.Entity.ModelConfiguration.Conventions namespace.
You can further configure your model by using data annotations or the fluent API. Precedence is given to configuration through the fluent API followed by data annotations and then conventions. For more information see Data Annotations, Fluent API - Relationships, Fluent API - Types & Properties and Fluent API with VB.NET.
Here you find more about Entity Framework Code First Conventions
You set wrong ids name as FK and PK, you need add primary key for Attendance also,follow code first conventions name, change your model like:
public class Employee
{
public Employee()
{
Attendances = new List<Attendance>();
}
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public long EmployeeId { get; set; }
public string Fullname { get; set; }
public virtual ICollection<Attendance> Attendances { get; set; }
}
public class Attendance
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public long AttendanceId { get; set; }
public DateTime CheckinDateTime { get; set; }
public DateTime? CheckoutDateTime { get; set; }
[Required]
[ForeignKey("Employee")]
public long EmployeeId { get; set; }
public virtual Employee Employee { get; set; }
}
ForeignKey attribute is applied on Attendance navigation property to specify foreignkey property name for Attendance property.
Without DataAnnotation we can use Fluent API for configuration our relationship. Ofcourse you need use code first convention names
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
//one-to-many
modelBuilder.Entity<Attendance>()
.HasRequired<Employee>(e => e.Employee) // Attendance entity requires Employee
.WithMany(a => a.Attendances); // Employee entity includes many Attendances entities
}
If your model not contains convention name, using Fluent API can use .HasForeignKey() and set specific name FK
public class Attendance
{
public long AttendanceId { get; set; }
public DateTime CheckinDateTime { get; set; }
public DateTime? CheckoutDateTime { get; set; }
//Not first code convention name
public long EmpId { get; set; }
public virtual Employee Employee { get; set; }
}
.
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
//one-to-many
modelBuilder.Entity<Attendance>()
.HasRequired<Employee>(e => e.Employee)
.WithMany(a => a.Attendances)
.HasForeignKey(e => e.EmpId);
}