EF InvalidCastException具有一对多关系

Question

I have am getting an InvalidCaseException when adding a one to many relationship entity. It fails on the Add not on the SaveChanges.

Unable to cast object of type 'System.Collections.Generic.List`1[UserAccount]' to type 'UserAccount'.

It is tring to case a collection of X to one instance of X

(Parent or One Entity)

[System.Xml.Serialization.XmlRootAttribute(Namespace="", IsNullable=false), Serializable()]
public class Merchant
{   

    /// <summary>
    /// Standard ID
    /// </summary>
    [Key]
    [DatabaseGenerated(System.ComponentModel.DataAnnotations.Schema.DatabaseGeneratedOption.Identity)]
    public int ID { get; set; }
    [DataType(DataType.Text), MaxLength(100)]
    /// <summary>
    /// UserFriendly Name 
    /// </summary>
    public string MerchantName { get; set; }

    /// Billing Information
    /// </summary>
    public virtual ICollection<BillingTransactions> BillingTransactions { get; set; }

    /// <summary>
    /// List of Accounts for this merchant  (pulled from DBAccounts)
    /// </summary>
    public virtual ICollection<UserAccount> UserAccounts { get; set; }
 }

(The Child or Many)

public class UserAccount
{

    private string loginID;
    [Key]
    [DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
    /// <summary>
    /// Standard ID 
    /// </summary>
    public int ID { get; set; }

    public int MerchantId { get; set; }

    [ForeignKey("ID")]    
    public Merchant Merchant { get; set; }
  //Obviously there are more properties here....
 }

I create the new entity as follows:

 public void CreateNewMerchant(UserAccount useraccount)
    {
        Merchant merchant;
        if (useraccount.Merchant == null) //New unknown merchant
        {
            merchant = new Model.Merchant.Merchant();
            merchant.UserAccounts = new List<UserAccount>();
            merchant.UserAccounts.Add(useraccount);
        }
        else
        {
            merchant = useraccount.Merchant;
        }

        ServiceBase<Merchant> sb = new Core.ServiceBase<Merchant>();
        base.Add(merchant); 
        base.Save();




    }

This is for a wizard like form interface. The first step is to create a useraccount. The next step is to fill in the new merchant information. The Wizard steps are creating the child object useraccount and an empty parent and then creating the parent in the next step.

My code is creating a blank/empty parent and adding the child/useraccount to the empty merchant and adding to the database.

Why am I getting an invalid cast exception?

Answer 1

You need...

[ForeignKey("MerchantId")]
public Merchant Merchant { get; set; }

...instead of [ForeignKey("ID")] which will use the primary key as the foreign key and hence define a one-to-one instead of a one-to-many relationship.