Entity Framework throwing InvalidOperationException when trying to load child tables

Question

I am using Entity Framework with asp .net mvc. I have a repository class that initializes an instance of the entities in the constructor. Let's say I have the familiar customers table that has 1 to many rows in an orders table: Customer has many orders.

I have tried the following 2 ways to load the orders associated with customer, but without success.

Attempt 1: Use Include
Result: Throws InvalidOperationException "The Value property has already been set on this EntityReference. More than one related object cannot be added to an EntityReference".

public List<Customer> GetCustomerList()
{
  return _database.CustomerSet.Include("Orders").ToList();
}

Attempt 2: Use Load
Result: Same exception, thrown on cust.Orders.Load()

public List<Customer> GetCustomerList()
{
  List<Customer> customers = _database.CustomerSet.ToList();
  foreach(Customer cust in customers)
  {
     if(!cust.Orders.IsLoaded)
     {
        cust.Orders.Load();
     }
  }
}

Is anyone familiar with this exception? Any suggestions on what might be the cause of this?

After using profiler, I know that it executes this query successfully to get all customers:

SELECT 1 AS [C1], [Extent1].[Name] AS [Name] .... 
FROM [dbo].[Customer] AS [Extent1]

Executes this query to get orders associated with the first customer (id=31):

SELECT 1 AS [C1], [Extent1].[ID] AS [ID] ... 
FROM [dbo].[Orders] AS [Extent1] 
WHERE [Extent1].[Customer_ID] = 31

It blows up after this, when it's associating the data pulled back from this query to the Customer model.

Answer 1

Looks like your assotiation is wrong and EF thinks that Customer can have only 1 order.