entity-framework - 基本 F#/ Entity Framework /通用函数

Question

在开发方面，我是一个完全的初学者，所以对于我对这里术语的理解不佳，提前道歉...

我正在尝试在 SQL 数据库中创建一些非常简单的不相关表，只是为了让我的头脑清醒过来。我想使用 Entity Framework 来引用这些内容，并且我想尽可能减少重复。我试图了解是否有更优雅的方法来执行此操作，这样我就不必每次都重新编写 getter 和 setter:

// First open "System; System.Data; System.Data.Entity; System.ComponentModel.DataAnnotations" 
// Then define "connectionString"
// Then create two simple classes that have no relation to each other, using CLIMutable 
// to help Entity Framework along.

module Model = 
    [<CLIMutable>] type Customer = {[<Key>]Id: int; FirstName: string; LastName: string;}
    [<CLIMutable>] type Item = {[<Key>]Id: int; ItemName: string; ItemDescription: string;}

module Actions =
    open Model
    type Context() =
        inherit DbContext()

        [<DefaultValue>] val mutable customers: DbSet<Customer> 
            member public this.Customers with get() = this.customers
                                           and  set v = this.customers <- v

        [<DefaultValue>] val mutable items: DbSet<Item>
            member public this.Items with get() = this.items
                                           and  set v = this.items <- v

// I would like to be able to add several more very simple classes without having to 
// repetively type out the getters and setters each time. Ideally I'd like to turn the above 
// into a generic function (method? I'm not sure of terminology) that I can call later and 
// pass it my desired parameters in terms of table/object names. However, if I move the code 
// above the Model and replace DbSet<Customer> with DbSet<'T> this won't work since it won't 
// know what type 'T is at this point. I suspect I need a generic function (method?) that 
// I can create a new instance of later and replace the generics with actual values (using 
// reflection?). Is there any way to do this without making Entity Framework get upset?

    let db = new Context()
    db.Database.Connection.ConnectionString <- Settings.connectionString

同样，我想创建一个执行 Add() 和 SaveChanges() 步骤的通用函数下面，但我不确定这是否可行，因为我需要动态替换带有我传入的表名的“客户”或“项目”——以及“t”的类型可能会有所不同，具体取决于调用该函数的内容，我不知道这是否被允许。

    let createCustomer id firstName lastName = 
        let t : Customer = {Id = id;FirstName = firstName; LastName = lastName}
        db.Customers.Add(t) |> ignore
        db.SaveChanges() |> ignore

    let createItem id itemName itemDescription = 
        let t : Item = {Id = id; ItemName = itemName; ItemDescription = itemDescription}
        db.Items.Add(t) |> ignore
        db.SaveChanges() |> ignore

open Actions
[<EntryPoint>]
let main argv =     
    createCustomer 1 "Bob" "Smith"
    createItem 1 "First item" "First item test"

    Console.ReadLine() |> ignore
    0

感谢您的帮助，请理解我的问题可能非常基本，所以如果人们不愿意重写代码但能够为我指出正确的资源方向以供进一步阅读，那就太好了!

[edit] 非常感谢 Fyodor 提供解决方案。关键是在一般引用“db”元素时将“:上下文”类型注释添加到它。此外，我犯了一个愚蠢的错误，即在我的主要论点中没有打开“模型”模块。更新和工作代码如下:

module Model = 
    [<CLIMutable>] type Customer = {[<Key>]Id: int; FirstName: string; LastName: string;}

module Actions =
    open Model
    type Context() =
        inherit DbContext()
        member val Customers: DbSet<Customer> = null with get, set

    let db = new Context()
    db.Database.Connection.ConnectionString <- Settings.connectionString

    let addAndCommit (db : Context) x =
        db.Set().Add x |> ignore
        db.SaveChanges() |> ignore

    let createCustomer id firstName lastName = 
        addAndCommit db {Id = id; FirstName = firstName; LastName = lastName}

open Actions
open Model
[<EntryPoint>]
let main argv =     
    createCustomer 1 "Bob" "Smith"
    Console.ReadLine() |> ignore
    0

Answer 1

首先，要声明带有支持字段的属性，请使用 member val :

type Context() =
    ...
    member val Customers: DbSet<Customer> = null with get, set
    ...

其次，访问一个DbSet特定类型的，您不需要属性。您可以通过 DbContext.Set<'t> 获取方法:

let addAndCommit (db: Context) (x: 't) =
    db.Set<'t>().Add x |> ignore
    db.SaveChanges() |> ignore

let createCustomer id firstName lastName = 
    addAndCommit db {Id = id; FirstName = firstName; LastName = lastName}

但是明确的't注释并不是真正需要的:F# 可以为您推断出来。

let addAndCommit (db: Context) x =
    db.Set().Add x |> ignore
    db.SaveChanges() |> ignore