ASP.NET MVC 5 Model Navigation Properties Error - asp.net-mvc

Question

So I have two models that I am trying to get working,
public class Contract
{
[Key]
public int Id { get; set; }
public string AwardId { get; set; }
[ForeignKey("Id")]
public virtual ICollection<ContractHistory> contractHistory { get; set; }
}
And
public class ContractHistory
{
[Key]
public int Id { get; set; }
public string AwardId { get; set; }
[ForeignKey("Id")]
public virtual Contract contract { get; set; }
}
There are many ContractHistory related to one Contract.
I keep getting a run-time InvalidCastException with that setup but when I remove the navigation property within the ContractHistory, and modify the Contract navigation property to:
public virtual ContractHistory contractHistory { get; set; }
It performs the join correctly without any errors.
I only have a year of experience working with .NET and at a lose as to what the issue could be. Ideally, I would like to navigate from Contract to a list of ContractHistory and from ContractHistory to one Contract. Worst case would be for me to create independent data repository methods to explicitly pull in these records but would prefer to figure out the solution to this problem for future reference.
Any advice or follow up questions are welcomed and thanks in advance!

Answer 1

Your ContractHistory class does not have a foreign key property.
Furthermore, you don't need to have the ForeignKeyAttribute overtop of public virtual ICollection<ContractHistory> contractHistory { get; set; } because you should be referencing the foreign key in the ContractHistory class.
The ForeignKeyAttribute constructor takes a string as a parameter.
Per MSDN
Parameters
name
Type: System.String
If you add the ForeigKey attribute to a foreign key property, you should specify the name of the associated navigation property. If you add the ForeigKey attribute to a navigation property, you should specify the name of the associated foreign key(s). If a navigation property has multiple foreign keys, use comma to separate the list of foreign key names.
So in your case:
[ForeignKey("Id")]
public virtual Contract contract { get; set; }
You are placing the ForeignKeyAttribute on the navigation property, contract. So essentially your class will search for a property called Id and identify that as the foreign key. But in your class, Id has the Key attribute which means you are declaring that as your primary key.
So in order to resolve this, you need to add another property to your ContractHistory class that will be the foreign key. And then change the string in your ForeignKeyAttribute to the name of that property.
Example:
public class ContractHistory
{
[Key]
public int Id { get; set; }
public string AwardId { get; set; }
public int contractID {get;set;}
[ForeignKey("contractID")]
public virtual Contract contract { get; set; }
}
Hope this helps!

Answer 2

As far as I see you want to implement one-to-many relationship, if so you have to remove the foreginkey attribute from the contract history collection in the contract class, and add contractId property as foreignkey in the contract history class as below:
public class Contract {
[Key]
public int Id { get; set; }
public string AwardId { get; set; }
public virtual ICollection<ContractHistory> contractHistory { get; set; }
}
public class ContractHistory {
[Key]
public int Id { get; set; }
public string AwardId { get; set; }
public int ContractId { get; set;}
[ForeignKey("ContractId")]
public virtual Contract contract { get; set; }
}