从基础扩展数据库对象/下传

Question

我正在学习F#，为了变得更流利，我正在重写一个后端/数据访问层，这个程序目前正在使用C#和ORM。我正在使用SqlDataProvider类型提供程序(顺便说一句，我也很喜欢它)。

我在F#中搜索的部分类类型没有显示出任何有希望的结果。部分类的原因是要向从Sql类型提供程序返回的数据库对象添加一些基本功能。到目前为止，我只是从Sql类型提供程序返回的类型继承，并以这种方式添加功能。但是，当我从函数返回查询结果时，它返回的是基类，而不是派生类。

我不想使用反射在两个对象的属性之间映射，但我也不希望在每次创建新方法时返回一个“新fooObject {. }”并列出每个属性。

所以我在这里，在这个世界上一切都是美好的源头。我是不是遗漏了一些可以用于部分类创建的东西？是否有一种简单的方法(不使用反射)将返回的对象映射到派生对象？我是不是完全错过了一些很棒的功能？

type DbContext = SqlDataConnection<ConnectionString="~">

//Database objects 
type Address() = 
    //inheriting base class from SqlDataProvider
    inherit DbContext.ServiceTypes.Address()

    //Adding common functionality
    member this.Add()  =
        use db = DbContext.GetDataContext()
        db.Address.InsertOnSubmit this
        db.DataContext.SubmitChanges()

    member this.Remove() = 
        use db = DbContext.GetDataContext()
        db.Address.DeleteOnSubmit this
        db.DataContext.SubmitChanges()

    member this.Update() =
        use db = DbContext.GetDataContext()
        let mutable old = query {for a in db.Address do
                                 where (a.AddressId = this.AddressId)}
                                 |> Seq.exactlyOne 
        old <- this
        db.Address.Context.SubmitChanges()

     //this method only returns the base object
    static member GetAll() =
        use db = DbContext.GetDataContext()
        db.Address |> Seq.toList

     //as does this one
    static member Find addressId = 
        use db = DbContext.GetDataContext()
        let add = new Address()
        query {for a in db.Address do where (a.AddressId = addressId)}
        |> Seq.exactlyOne

Answer 1

F#用类型扩展做这种事

type DbContext.ServiceTypes.Address with
    member this.Add() =
        use db = DbContext.GetDataContext()
        db.Address.InsertOnSubmit this
        db.DataContext.SubmitChanges()

    member this.Remove() = 
        use db = DbContext.GetDataContext()
        db.Address.DeleteOnSubmit this
        db.DataContext.SubmitChanges()

    member this.Update() =
        use db = DbContext.GetDataContext()
        let mutable old = query {for a in db.Address do
                                 where (a.AddressId = this.AddressId)}
                                 |> Seq.exactlyOne 
        old <- this
        db.Address.Context.SubmitChanges()

注意，类型扩展(以这种格式)只能从F#代码中访问。如果您需要与C#/VB.Net进行互操作，则应该使用“正常”扩展方法：

[<Extension>]
type ExtraCSharpStyleExtensionMethodsInFSharp () =
    [<Extension>]
    static member this.Add (address:DbContext.ServiceTypes.Address)  =
        use db = DbContext.GetDataContext()
        db.Address.InsertOnSubmit address
        db.DataContext.SubmitChanges()

    [<Extension>]
    member this.Remove (address:DbContext.ServiceTypes.Address) = 
        use db = DbContext.GetDataContext()
        db.Address.DeleteOnSubmit address
        db.DataContext.SubmitChanges()

    [<Extension>]
    member this.Update (address:DbContext.ServiceTypes.Address) =
        use db = DbContext.GetDataContext()
        let mutable old = query {for a in db.Address do
                                    where (a.AddressId = this.AddressId)}
                                    |> Seq.exactlyOne 
        old <- address
        db.Address.Context.SubmitChanges()

至于GetAll和Find方法，我很想创建一个功能像GetAllAddresses和FindAddress这样的模块。

总的来说，存储库模式在F#中有点笨拙。