在ASP.NET MVC3项目中编写多态对象

Question

我的问题的本质是如何用MVC3和Ninject以合理的方式组合这些对象(见下文)(尽管我不确定DI应该在解决方案中发挥作用).我无法透露我的项目的真实细节,但这是一个近似,说明了问题/问题.在VB或C#中的答案表示赞赏!

我有几种不同的产品,具有各种各样的特性,但它们都需要在目录中表示.每个产品类在我的数据库中都有一个对应的表.商品具有一些特定于商品的属性,因此拥有自己的表.我已经为目录条目定义了一个接口,其目的是调用DescriptionText属性将根据底层的具体类型给出非常不同的结果.

Public Class Clothing
    Property Identity as Int64
    Property AvailableSizes As List(Of String)
    Property AvailableColor As List(Of String)
End Class

Public Class Fasteners
    Property Identity as Int64
    Property AvailableSizes As List(Of String)
    Property AvailableFinishes As List(Of String)
    Property IsMetric As Boolean
End Class

Public Interface ICatalogEntry
    Property ProductId as Int64
    Property PublishedOn As DateTime
    Property DescriptionText As String
End Interface

鉴于DescriptionText是表示层关注的问题,我不想在我的产品类中实现ICatalogEntry接口.相反,我想将其委托给某种格式化程序.

Public Interface ICatalogEntryFormatter
    Property DescriptionText As String
End Interface

Public Class ClothingCatalogEntryFormatter
    Implements ICatalogEntryFormatter

    Property DescriptionText As String
End Class

Public Class FastenerCatalogEntryFormatter
    Implements ICatalogEntryFormatter

    Property DescriptionText As String
End Class

在一个控制器的某个地方会有这样的代码:

Dim entries As List(Of ICatalogEntry)
                   = catalogService.CurrentCatalog(DateTime.Now)

在某个地方的视图中会有这样的代码:

<ul>
@For Each entry As ICatalogEntry In Model.Catalog
    @<li>@entry.DescriptionText</li>
Next
</ul>

所以问题是构造函数是什么样的？如何设置它以便在适当的位置实例化适当的对象.看起来像仿制药或DI可能有助于此,但我似乎有一个心理障碍.我想出的唯一想法是将一个ProductType属性添加到ICatalogEntry,然后实现这样的工厂:

Public Class CatalogEntryFactory
    Public Function Create(catEntry as ICatalogEntry) As ICatalogEntry
        Select Case catEntry.ProductType
        Case "Clothing"
            Dim clothingProduct = clothingService.Get(catEntry.ProductId)
            Dim clothingEntry = New ClothingCatalogEntry(clothingProduct)
            Return result
        Case "Fastener"
            Dim fastenerProduct = fastenerService.Get(catEntry.ProductId)
            Dim fastenerEntry = New FastenerCatalogEntry(fastenerProduct)
            fastenerEntry.Formatter = New FastenerCatalogEntryFormatter
            Return fastenerEntry
    ...     
    End Function
End Class

Public ClothingCatalogEntry
    Public Sub New (product As ClothingProduct)
        Me.Formatter =  New ClothingCatalogEntryFormatter(product)
    End Sub

    Property DescriptionText As String
        Get
            Return Me.Formatter.DescriptionText
        End Get
    End Property
End Class

...FastenerCatalogEntry is omitted but you get the idea...

Public Class CatalogService
    Public Function CurrentCatalog(currentDate as DateTime)
        Dim theCatalog As List(Of ICatalogEntry)
                                  = Me.repository.GetCatalog(currentDate)

        Dim theResult As New List(Of ICatalogEntry)

        For Each entry As ICataLogEntry In theCatalog
            theResult.Add(factory.Create(entry))
        Next

        Return theResult
    End Function
End Class

恕我直言,除了必须为每个新产品类别更改工厂外,我并没有真正得到这些代码的任何气味.然而,我的直觉说这是旧的做事方式,而现在DI和/或仿制药可以更好地做到这一点.关于如何处理这个问题的建议非常感谢(关于更好标题的建议......)

Answer 1

因此，我做了一些小改动，使用 Ninject Factory 扩展使其正常工作。最大的变化是我的实体有足够的信息来显示任一类型（在我设计的示例中为衣服或紧固件），如果该项目实际上是衣服，则紧固件特定属性将为空，反之亦然。

Public Interface IDescribable
    ReadOnly Property DescriptionText As String
End Interface

Public Enum ProductType
    CLOTHING
    FASTENER
End Enum

Public Interface ICatalogEntry
    Inherits IDescribable
    ReadOnly Property ProductId As Int64
    ReadOnly Property PublishedOn As DateTime
    ReadOnly Property ProductType As ProductType
End Interface

Public Class CatalogEntryEntity
    Public Property ProductId As Long
    Public Property ProductType As ProductType
    Public Property PublishedOn As Date
    Public Property DescriptionText As String
    Public Property Color As String
    Public Property Finish As String
    Public Property IsMetric As Boolean
End Class

然后，我可以定义我的目录服务，如下所示：

Public Class CatalogService
    Private ReadOnly _factory As ICatalogEntryFactory
    Private ReadOnly _repository As CatalogRepository

    Public Sub New(entryFactory As ICatalogEntryFactory, repository As CatalogRepository)
        Me._factory = entryFactory
        Me._repository = repository
    End Sub

    Public Function CurrentCatalog(currentDate As DateTime) As List(Of ICatalogEntry)
        Dim items = Me._repository.GetCatalog()
        Return (From item In items Select _factory.Create(item.ProductType.ToString(), item)).ToList()
    End Function
End Class

Public Interface ICatalogEntryFactory
    Function Create(bindingName As String, entity As CatalogEntryEntity) As ICatalogEntry
End Interface

假设我像这样设置绑定，Ninject 将提供工厂（这太棒了！）：

theKernel.Bind(Of ICatalogEntry)().To(Of ClothingCatalogEntry)().Named("CLOTHING")
theKernel.Bind(Of ICatalogEntry)().To(Of FastenerCatalogEntry)().Named("FASTENER")
theKernel.Bind(Of ICatalogEntryFactory)().ToFactory(Function() New UseFirstParameterAsNameInstanceProvider())

为了简洁起见，我省略了 FastenerCatalogEntry；ClothingCatalogEntry 是这样的：

Public Class ClothingCatalogEntry   
    Public Sub New(ByVal entity As CatalogEntryEntity)
...

这篇文章对我解决这个问题最有帮助。我完全按照此处所示使用 UseFirstParameterAsNameInstanceProvider 。