EF代码优先多个0到多

Question

I'm unable to add a second one-to-many (I'd prefer a zero-to-many)relationship to my class....

I'm also using the Entity First framework. I'm also using a single model with 4 different views. 2 of them should have a second x-to-many relationship with class A, and the other 2 should have a one-to-many relationship with class B. Here's how my classes look:

public class Request
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int ID { get; set; }
        ... 
        other properties
        ...         
        public virtual ICollection<OrderBasic> Orders { get; set; }
        public virtual ICollection<OrderExtended> ExtendedOrders { get; set; }

    public Request()
    {
        Orders = new List<OrderBasic>();
        ExtendedOrders = new List<OrderExtended>();
    }       
}

public class OrderBasic
{
    public int ID { get; set; }         
    ... 
    specific OrderBasic properties
    ...

    public int RequestRefId { get; set; }

    [ForeignKey("RequestRefId")]
    public virtual Request Request { get; set; }
}

public class OrderExtended
{
    public int ID { get; set; }         
    ... 
    specific OrderExtended properties
    ...
    public int RequestRefId { get; set; }

    [ForeignKey("RequestRefId")]
    public virtual Request Request { get; set; }
}

View which renders a different PartialView depending on the specific type of order I want. Works without issues for the BasicOrder type.

@model RFP_MVC.Models.Request

@using (Html.BeginForm()) 
{
    @Html.AntiForgeryToken()

    <div class="form-horizontal">
        <legend>General info:</legend>
        @Html.ValidationSummary(true, "", new { @class = "text-danger" })

    //Request Model properties...


        <table class="table table-striped" id="orderTable">
            <thead>
                <tr>
                    <th>Material</th>
                    <th>Quantity</th>
                    <th>Unit</th>
                    <th></th>
                </tr>
            </thead>
            <tbody id="OrderZone">
                @foreach (var row in Model.ExtendedOrders)
                {
                    Html.RenderPartial("~/Views/Orders/OrderExtendedCreate.cshtml", row);
                }
            </tbody>
        </table>
        <button class="btn btn-sm btn-success" type="button" id="addOrder">Add order</button>

        <div class="form-group">
            <div class="col-md-offset-2 col-md-10">
                <input type="submit" value="Create" class="btn btn-default" />
            </div>
        </div>
    </div>
}

DbContext class:

namespace RFP_MVC.DAL
{
    public class DatabaseContext : DbContext
    {
        public DbSet<Shipment> shipments { get; set; }
        public DbSet<Request> requests { get; set;  }
        public DbSet<OrderBasic> basicOrders { get; set; }
        public DbSet<OrderExtended> extendedOrders { get; set; }
    }
}

I then generate 4 different views based on a propery requestType. Two views have a collection of OrderBasic, the two other views should implement OrderExtended I then use a partial view to render properties of the order model. As long as I implement just the OrderBasic collection, I have no issues. When I add the second order model (OrderExtended) I receive the following EF related error:

An exception of type 'System.ArgumentNullException' occurred in EntityFramework.dll but was not handled in user code. Additional information: Value cannot be null.

The problem appears when I try to display the Index of a certain View, even if it's that of a completely unrelated model (Shipment in this case).

Answer 1

Looks like I found the the culprit. My model contains a file upload:

    [DataType(DataType.Upload)]
    public HttpPostedFileBase Attachment { get; set; }

Which yielded the following error as soon as I tried to add a migration:

Value cannot be null.
Parameter name: entitySet

HttpPostedFileBase isn't supported by EF. I'll have to add a property which just stores a reference to the file location, instead of storing the actual file in my DB. Something like this:

 [NotMapped]
 [DataType(DataType.Upload)]
 public HttpPostedFileBase Attachment{ get; set; } //file to pass to controller
 public string FilePath { get; set;  } //reference to file path