NullReferenceException与自动生成的表

Question

我有一个由EF自动生成并包含ICollection列表和应该在构造函数中初始化的列表的Exception NullReferenceException ...类的问题，但是当尝试向列表中添加项目时，它会显示Exception。

internal partial class Customer : Person
{

    partial void ObjectPropertyChanged(string propertyName);

    public Customer()
    {
        this.Accounts = new HashSet<Account>();
        this.CustomerUpdates = new HashSet<CustomerUpdate>();
    }

    public virtual ICollection<Account> Accounts { get; set; }
    public virtual ICollection<CustomerUpdate> CustomerUpdates { get; set; }
}

尝试向集合中添加任何项目时抛出该异常。 “ this.Accounts.Add（）”

internal partial class Customer : Person, ICustomer
{
    internal Customer(Guid userId, string firstName, string surname)
        : base(userId, firstName, surname) {  }

    //List of customer accounts
    IEnumerable<IAccount> ICustomer.Accounts
    {
        get { return Accounts.AsEnumerable<IAccount>(); }
    }

    //Open SavingsAccount
    public Account OpenSavingsAccount(decimal amount)
    {
        var account = new AccountSavings();
        account.Debit(amount, "-- Opening Balance --");
        this.Accounts.Add(account);
        return account;           
    }

    //Open LoanAccount
    public Account OpenLoanAccount(decimal amount)
    {
        var account = new AccountLoan(amount);
        account.Debit(amount, "-- Opening Balance --");
        this.Accounts.Add(account);
        return account;
    }

Answer 1

仅当您在查询中使用.Include(o => o.Accounts) ，Entity Framework才会初始化集合。

如果没有，则必须自己初始化列表：

if (this.Accounts == null)
    this.Accounts = new List<Account>();
this.Accounts.Add(account);