小编ifo*_*ooi的帖子

我有基础抽象Goods类和继承Book类.

abstract class Goods
{
    public decimal weight; 
    string Title, BarCode;
    double Price;
    public Goods(string title, string barCode, double price)
    {
        Title = title;
        BarCode = barCode;
        Price = price;
    }
}

abstract class Book : Goods
{
    protected int NumPages;
    public Book(string title, string barCode, double price, int numPages)
        : base(title, barCode, price)
    {
        NumPages = numPages;
        weight = 1;
    }
    public override void display()
    {
        base.display();
        Console.WriteLine("Page Numbers:{0}", NumPages);
    }

}

我应该写title, …

我想做adapter模板。
Move()中有错误AutoToTravelAdapter；方法 我该如何override和inherit运输方法？我尝试使用虚拟但它不起作用。我在两个适配器中更改为 public override void Move() 并且有效！谢谢，佐哈尔·佩莱德！

using System;

namespace Adapter
{

    class Program
    {
        static void Main(string[] args)
        {
            Traveller traveller = new Traveller();
            Transport camelTransport = new CamelToTravelAdapter();
            Transport autoTransport = new AutoToTravelAdapter();
            traveller.Travel(camelTransport);
            traveller.Travel(autoTransport);
            Console.Read();
        }
    }

     public class Transport
    {
       virtual public   void Move() { Console.WriteLine("trans Moves"); }
    }
    class Auto
    {
        public void Drive()
        {
            Console.WriteLine("Car drive");
        }
    }
    class Traveller
    {
        public void …

System.InvalidOperationException: The instance of entity type 'ProjectAssignment' cannot be tracked because another instance with the same key value for {'ProjectID'} is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see the conflicting key values.
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IdentityMap`1.Add(TKey key, InternalEntityEntry entry)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.St

我制作了一个带有Worker（ID和其他列）和Project（ID和其他列）Entity和ProjectAssignment（许多ID分配给许多Workers）的项目。但是，当我尝试获取ProjectAssignment数据时，会出现Application Insights中的错误。奇怪的是，该ID并未更早出现。

这是https://github.com/Streamc/ContosoObserve1/tree/master/Proj_s

 context.Database.EnsureCreated();

  var ProjectAssignments = new ProjectAssignment[]
             {
                    new ProjectAssignment
                    {
                        ProjectID = Projects.Single( i => i.ID == 1).ID,
                        WorkerID …

 Either target .NET Core 2.0 or lower, or use a version of the .NET SDK that supports .NET Core 2.1.    Microsoft.AspNetCore.Identity.Test  C:\Program Files\dotnet\sdk\2.1.4\Sdks\Microsoft.NET.Sdk\build\Microsoft.NET.TargetFrameworkInference

我尝试构建Microsoft示例https://github.com/aspnet/Identity/tree/dev/samples/IdentitySample.Mvc

我安装了Netcore SDK 2.1.4

dotnet --info 显示2.0.5

为什么会出现错误？

我尝试在 SQL Server 中执行 SQL-1999 样式递归

 CREATE TABLE addressparts(
    AddrPartId INTEGER NOT NULL,
    ParentID INTEGER NOT NULL,
    AddrPartTypeId VARCHAR(30),
    Name VARCHAR(30),
    constraint PK_OBJECTS primary key (AddrPartId))

insert into addressparts values (1, 0, 'country','Zimbabwe');
insert into addressparts values (2, 1, 'city','zi');
insert into addressparts values (3, 2, 'subcity','kalkli');
insert into addressparts values (4, 2, 'subcity','kalkli1');

我想要选择递归查询

WITH 
 Rec (AddrPartId, ParentID, AddrPartTypeId, name)
 AS (
   SELECT AddrPartId, ParentID, AddrPartTypeId, name FROM addressparts
   UNION ALL
   SELECT Rec.AddrPartId, Rec.ParentID, rec.AddrPartTypeId, Rec.name
    FROM Rec
    inner …

我尝试为Visual Studio 2017做Razor ContosoUniversity(最初在ContsoObserve中重命名)并得到错误我的.csproj是

<Project Sdk="Microsoft.NET.Sdk.Web">
  <PropertyGroup>
    <TargetFramework>netcoreapp2.0</TargetFramework>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Design" Version="2.0.1" />
    <PackageReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Tools" Version="2.0.1" />
    <PackageReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Utils" Version="2.0.1" />
  </ItemGroup>
  <ItemGroup>
    <PackageReference Update="Microsoft.NETCore.App" Version="2.0.4" />
  </ItemGroup>
  <ItemGroup>
        <DotNetCliToolReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Tools" Version="2.0.1" />
    </ItemGroup>
</Project>

我在NuGet中安装了所有软件包

当我

dotnet aspnet-codegenerator razorpage -m Student -dc SchoolContext -udl -outDir Pages\Students --referenceScriptLibraries

得到

建立失败.Data\SchoolContext.cs(5,17):错误CS0234:命名空间"Microsoft"中不存在类型或命名空间名称"EntityFrameworkCore"(您是否缺少程序集引用？)[C:\ Users\STR\source\repos\ContosoObserve\ContosoObserve\ContosoObserve.csproj] Pages\About.cshtml.cs(5,32):错误CS0234:命名空间"Microsoft.AspNetCore.Mvc"中不存在类型或命名空间名称"RazorPages"(是你吗？缺少程序集引用？)[C:\ Users\STR\source\repos\ContosoObserve\ContosoObserve\ContosoObserve.csproj] Pages\Contact.cshtml.cs(5,32):error CS0234:类型或命名空间名称'RazorPages'在命名空间 'Microsoft.AspNetCore.Mvc'(？是否缺少的组件参考)不存在[C:\用户\ STR \源\回购\ ContosoObserve\ContosoObserve\ContosoObserve.csproj]页\ Error.cshtml.cs( 6,32):错误CS0234:命名空间"Microsoft.AspNetCore.Mvc"中不存在类型或命名空间名称"RazorPages"(您是否缺少程序集引用？)[C:\ Users\STR\source\repos\Conto soObserve\ContosoObserve\ContosoObserve.csproj] Pages\Index.cshtml.cs(6,32):错误CS0234:命名空间"Microsoft.AspNetCore.Mvc"中不存在类型或命名空间名称"RazorPages"(你错过了吗？程序集引用？)[C:\ Users\STR\source\repos\ContosoObserve\ContosoObserve\ContosoObserve.csproj] Program.cs(7,28):error CS0234:命名空间中不存在类型或命名空间名称"Hosting" 'Microsoft.AspNetCore'(您是否缺少程序集引用？)[C:\ Users\STR\source\repos\ContosoObserve\ContosoObserve\ContosoObserve.csproj] Program.cs(8,28):error CS0234:类型或命名空间名称"配置"在名称空间"Microsoft.Extensions"中不存在(您是否缺少程序集引用？)[C:\ Users\STR\source\repos\ContosoObserve\ContosoObserve\ContosoObserve.csproj] Program.cs(9, 28):错误CS0234:命名空间"Microsoft.Extensions"中不存在类型或命名空间名称"Logging"(您是否缺少程序集引用？)[C:\ Users\STR\source\repos\C ontosoObserve\ContosoObserve\ContosoObserve.csproj] Startup.cs(5,28):错误CS0234:命名空间"Microsoft.AspNetCore"中不存在类型或命名空间名称"Builder"(您是否缺少程序集引用？)[C :\ Users\STR\source\repos\ContosoObserve\ContosoObserve\ContosoObserve.csproj] …

Here is example of Albahari

public class Stack
{
int position;
object[] data = new object[10]; // Why 10 nor 1? 
public void Push (object obj) { data[position++] = obj; } //do not understood; Why there is no loop
public object Pop() { return data[--position]; } //do not understood Why there is no loop
}

Stack stack = new Stack();
stack.Push ("sausage");
string s = (string) stack.Pop(); // Downcast, so explicit cast is needed
Console.WriteLine (s); // sausage

I rewrote …

我有

CmdString = "insert into Team_table (name1, name2, result1, result2) (select t1.name,t2.name,NULL,NULL from teams t2 cross join teams t1)";

我把它分成两列,按压输入就像输入一样

CmdString = "insert into Team_table (name1, name2, result1, result2) 
(select t1.name,t2.name,NULL,NULL from teams t2 cross join teams t1)";

errore出现了

我怎么解决这个问题？