映射到两个不同的集合类型时引发AutoMapper异常

Question

我正在编写一个使用AutoMapper进行对象映射的ASP.NET Web API服务。我正在针对AbleCommerce购物车软件构建此服务。问题中的服务(目的地)类跟踪用户及其地址。

public class UserModel
{
    public int UserID { get; set; }
    ...
    public List<AddressModel> Addresses { get; set; }
}

public class AddressModel 
{
    public int AddressID { get; set; }
    public int UserID { get; set; }
    ...
    // Contains some of the fields from AbleCommerce Address
}

我的源代码是AbleCommerce包中的User和Address类。我包含了祖先类的类声明，因为我认为泛型约束的使用可能会有问题，但我不能完全确定。

public class User: IPersistable
{
    public int UserId { get; set; }
    ...
    public AddressCollection Addresses 
    {
        get
        {
            // Calls an internal method which creates a new instance
            // of AddressCollection and loads the addresses for the
            // user from the database.
            ...
            return _Addresses;
        }
    }
}

public class Address : IPersistable 
{ 
    public int AddressId { get; set; }
    public int UserId { get; set; }
    ... 
}

public class AddressCollection : PersistentCollection<Address> { ... }

public class PersistentCollection<T> : SortableCollection<T> where T : IPersistable { ... }

public interface IPersistable { ... }

从AbleCommerce类到我的服务类的映射按预期工作。只要我在映射配置中忽略不需要的属性，从我的服务类到AbleCommerce类的映射就可以工作。但是，在Addresses属性的情况下，我不知道如何解决AbleCommerce User类中的AddressCollection和我的服务的UserModel类中的List<AddressModel>之间的差异(从AutoMapper的角度来看)。

当我测试映射配置时，我得到的异常是：

AutoMapper.AutoMapperConfigurationException : The following property on AlfredModel.Models.Classes.AddressModel cannot be mapped: 
    Addresses
Add a custom mapping expression, ignore, add a custom resolver, or modify the destination type AlfredModel.Models.Classes.AddressModel.
Context:
    Mapping to property Addresses from System.Object to AlfredModel.Models.Classes.AddressModel
    Mapping to property Addresses from CommerceBuilder.Users.AddressCollection to System.Collections.Generic.List`1[[AlfredModel.Models.Classes.AddressModel, AlfredModel, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]]
    Mapping to property User from CommerceBuilder.Users.User to AlfredModel.Models.Classes.UserModel
    Mapping from type CommerceBuilder.Orders.Basket to AlfredModel.Models.Classes.BasketModel
Exception of type 'AutoMapper.AutoMapperConfigurationException' was thrown.
   at AutoMapper.ConfigurationStore.DryRunTypeMap(ICollection`1 typeMapsChecked, ResolutionContext context)
   at AutoMapper.ConfigurationStore.DryRunTypeMap(ICollection`1 typeMapsChecked, ResolutionContext context)
   at AutoMapper.ConfigurationStore.DryRunTypeMap(ICollection`1 typeMapsChecked, ResolutionContext context)
   at AutoMapper.ConfigurationStore.DryRunTypeMap(ICollection`1 typeMapsChecked, ResolutionContext context)
   at AutoMapper.ConfigurationStore.AssertConfigurationIsValid(IEnumerable`1 typeMaps)
   at AutoMapper.ConfigurationStore.AssertConfigurationIsValid()
   at AutoMapper.Mapper.AssertConfigurationIsValid()
   at AlfredModelTests.AlfredMapConfigurationTest.Maps_Configured_Correctly() in C:\Users\ntruick\Documents\Visual Studio 2010\Projects\AlfredModel\AlfredModelTests\AlfredMapConfigurationTest.cs:line 21

这让我感到困惑，因为AddressModel类没有一个名为Addresses的属性。很明显我漏掉了什么。如有任何建议、建议或澄清，我们将不胜感激。

Answer 1

我相信我已经找到了一个解决方案。经过大量的挖掘(以及一些值得称赞的地方)，我发现我需要通过为用户地址集合创建一个类型转换器来定义映射：

public class UserAddressesTypeConverter : 
    ITypeConverter<PersistentCollection<Address>, List<AddressModel>
{
    var source = (PersistentCollection<Address>)context.SourceValue;
    var result = new List<AddressModel>();

    foreach (Address address in source.Cast<Address>().ToList()
        result.Add(Mapper.Map<AddressModel>(address));

    return result;
}

我的困惑是基于这样一个事实:我试图直接使用AddressCollection类来完成类似的事情。似乎PersistentCollection上的泛型约束不允许子类正确解析为Address类型。一旦我改变了源代码，它只需要一个简单的LINQ Cast就可以让一切正常工作。