无法在带有 CustomType 的查询中转换为 IConvertible

Question

使用 NHibernate 会话运行此代码时：

_session.Query<Order>().SingleOrDefault(o => o.EmployeeNumber == employeeNumber);

我收到以下异常：

Unable to cast object of type 'EmployeeNumber' to type 'System.IConvertible'.

相关代码：

public class Order : FOAggregateRoot
{
    private readonly int _employeeNumber;
    public virtual EmployeeNumber EmployeeNumber => (EmployeeNumber)_employeeNumber;
    private readonly IList<OrderLine> _products;
    public virtual IReadOnlyList<OrderLine> Products => _products.ToList();
    public virtual Price Total => (Price)_products.Sum(line => line.Total);

    public Order(EmployeeNumber employeeNumber) : base(Guid.NewGuid())
    {
        _products = new List<OrderLine>();
        _employeeNumber = employeeNumber;
    }

    protected Order() { }
}

public sealed class EmployeeNumber : SingleValueObject<int>
{
    public EmployeeNumber(int value)
    {
        Value = value;
    }

    public static implicit operator int(EmployeeNumber number)
    {
        return number.Value;
    }

    public static explicit operator EmployeeNumber(int number)
    {
        return new EmployeeNumber(number);
    }
}

public class OrderMap : ClassMap<Order>
{
    public OrderMap()
    {
        Id(Entity.Expressions<Order>.Id);
        Map(x => x.Uid);
        Map(x => x.EmployeeNumber)
            .Unique()
            .CustomType<int>().Access.CamelCaseField(Prefix.Underscore);
        HasMany(x => x.Products)
            .Inverse()
            .Cascade.All()
            .Not.LazyLoad();
    }
}

我有点“理解”为什么会发生这个异常，我可以通过实现IConvertible （我不想要在我的值对象中）或明确地将employeeNumber IConvertible为int来解决它。

但是，我本来希望这段代码开箱即用，特别是因为我在EmployeeNumber定义了一个隐式转换为int operator ，但是 NHibernate 似乎没有使用它。

在这种情况下，是否可以通知 NHibernate 使用此operator ？

是否存在任何其他解决方案？ （理想情况下，如果它编译，它会运行）

我注定要使用两个第一个解决方案（IConvertible/explicit cast）中的一个吗？

Answer 1

解决方案是为我的不同值对象创建我自己的自定义类型：

public sealed class EmployeeNumberUserType : SingleValueObjectType<EmployeeNumber>
{
    protected override NullableType PrimitiveType => NHibernateUtil.Int32;
}

public abstract class SingleValueObjectType<TValueObject> : IUserType where TValueObject : class
{
    public SqlType[] SqlTypes => new[] { PrimitiveType.SqlType };

    public Type ReturnedType => typeof(TValueObject);

    public bool IsMutable => false;

    public object Assemble(object cached, object owner) => cached;

    public object DeepCopy(object value) => value;

    public object Disassemble(object value) => value;

    public new bool Equals(object x, object y) => x?.Equals(y) ?? y?.Equals(x) ?? true;

    public int GetHashCode(object x) => x?.GetHashCode() ?? 0;

    public object NullSafeGet(DbDataReader rs, string[] names, ISessionImplementor session, object owner)
    {
        var obj = PrimitiveType.NullSafeGet(rs, names[0], session, owner);
        if (obj == null) return null;
        else return Activator.CreateInstance(typeof(TValueObject), obj);
    }

    public void NullSafeSet(DbCommand cmd, object value, int index, ISessionImplementor session)
    {
        if (value == null) cmd.Parameters[index].Value = DBNull.Value;
        else cmd.Parameters[index].Value = value.GetType()
                                                .GetProperty("Value", BindingFlags.Instance | BindingFlags.NonPublic)
                                                .GetValue(value);
    }

    public object Replace(object original, object target, object owner) => original;

    protected abstract NullableType PrimitiveType { get; }
}

并在映射中明确使用此自定义类型：

public class OrderMap : ClassMap<Order>
{
    public OrderMap()
    {
        Id(Entity.Expressions<Order>.Id);
        Map(x => x.EmployeeNumber)
            .Unique()
            .CustomType<EmployeeNumberUserType>();
    }
}