小编Des*_*ino的帖子

我在这里按照EntityFrameworkCore教程 https://docs.efproject.net/en/staging/platforms/aspnetcore/new-db.html 但是当我到达教程的创建数据库部分 https://docs.efproject .net/en/staging/platforms/aspnetcore/new-db.html #create-your-database 并运行命令Add-Migration MyFirstMigration我收到以下错误:

Cannot execute this command because Microsoft.EntityFrameworkCore.Design is not installed. Install the version of that package that matches the installed version of Microsoft.EntityFrameworkCore and try again.

我尝试安装Microsoft.EntityFrameworkCore.Design以及Microsoft.EntityFrameworkCore.SqlServer.Design NuGet上的每个版本但仍然得到相同的错误.

我还尝试使用该命令在NuGet PM之外运行

• dotnet恢复
• dotnet ef migrations添加MyFirstMigration

并得到以下错误:

Unhandled Exception: System.MissingMethodException: Entry point not found in assembly 'Microsoft.EntityFrameworkCore.Design, Version=1.1.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60'.

我尝试了所有我能想到的东西,并在互联网上到处寻找,但仍然没有找到答案.

我有两种类型,它们共享一个命名值.

type Type1 = 
    {
        p1: int;
        p2: int;
    } 
type Type2 = 
    {
        p1 : int;
        p3 : int;
    }

是否可以创建仅更改此命名值(p1)并返回新记录的函数？

我试过这么远:

type IType = 
    abstract member p1: int;

type Type1 = 
    {
        p1: int;
        p2: int;
    } 
    interface IType with
        member this.p1 = this.p1

type Type2 = 
    {
        p1 : int;
        p3 : int;
    }
    interface IType with
        member this.p1 = this.p1

let changeP1ToTen (value: 'a when 'a :> IType) = 
    let newValue = {value with p1 = …

我刚刚开始使用F#,我的大脑已经破碎,试图弄清楚如何使用它的类型,而不必采用OO类型的编程.

这是我的情况我基本上想要创建一个方法,我提供类型和Id,它返回给我数据库中的对象.

所以基本上这就是我到目前为止所得到的.

let client = MongoClient()
let database = client.GetDatabase("testdb")

let lowerCase (str : string) = 
    str.ToLower()

let nameOf (classType: Type) = 
    classType.Name

let nameTypeOf<'a> = 
    nameOf typeof<'a>   

let getCollection<'a> =
    let collectionName = nameTypeOf<'a> |> lowerCase
    database.GetCollection<'a> collectionName

let dbSelect<'a> id = 
    let collection = getCollection<'a>
    collection.Find(fun(x) -> x.Id = id).First()

所以我的问题是使用dbSelect,显然它不编译,因为x是通用的,基本上我想创建一个带有Id的接口,所有我的对象都与它接口.我知道如何使用类和继承来实现它,但我避免在cop库之外使用实例化的类.如果有的话,最好的功能方法是什么.

这就是我所期待的

type IDbObject = 
    abstract Id: string

type Item = 
    {
        Id: string
        Name: string
    }
    interface IDbObject with
        member x.Id = x.Id

let item = …

所以我有一个简单的对象

type DbObject() = 
    member val Id = ObjectId.GenerateNewId().ToString() with get, set
    member val Name = "" with get, set
type Item() =
    inherit DbObject()
    member val Description = "" with get, set
    member val Refs : list<string> = [] with get, set

当我将它插入到我的 MongoDB 数据库中时，这工作得很好，但是每当我尝试接收它时，我都会收到以下错误。

System.FormatException: An error occurred while deserializing the Material property of class Item: Type 'Microsoft.FSharp.Collections.FSharpList`1[[System.String, System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]]' does not have a suitable constructor or Add method. ---> MongoDB.Bson.BsonSerializationException: Type 'Microsoft.FSharp.Collections.FSharpList`1[[System.String, System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, …