DbContextOptionsBuilder'不包含'usesqlserver'的定义，并且在asp.net core 2.2中没有扩展方法'usesqlserver'？

Question

项目版本：.netcore2.2

我正在使用 .netcore2.2 中的 N 层架构

当我定义下面的配置然后给出错误：

DbContextOptionsBuilder' 不包含 'usesqlserver' 的定义，也没有扩展方法 'usesqlserver'

    public class CustomerDataAccess : DbContext, ICustomerDataAccess
    {

        protected override void OnConfiguring(DbContextOptionsBuilder dbContextOptionsBuilder)
        {
            if (!dbContextOptionsBuilder.IsConfigured && _configuration.GetConnectionString("DMEBaseConnection") != null)
            {
                dbContextOptionsBuilder.UseSqlServer(_configuration.GetConnectionString("connectionstringname")); **//here give an error**
            }
        }

startup.cs

    public class Startup
    {
        // This method gets called by the runtime. Use this method to add services to the container.
        // For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=398940
        public void ConfigureServices(IServiceCollection services)
        {
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.Run(async (context) =>
            {
                await context.Response.WriteAsync("Hello World!");
            });
        }
    }

程序.cs

namespace projectname
{
    public class Program
    {
        public static void Main(string[] args)
        {
            CreateWebHostBuilder(args).Build().Run();
        }

        public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
            WebHost.CreateDefaultBuilder(args)
                .UseStartup<Startup>();
    }
}

见下图：

当我安装这个时：

Install-Package Microsoft.EntityFrameworkCore.SqlServer
Install-Package Microsoft.EntityFrameworkCore.SqlServer -Version 2.2.6
Install-Package Microsoft.EntityFrameworkCore.SqlServer -Version 3.1.2

当前错误：

NU1608: Detected package version outside of dependency constraint: Microsoft.AspNetCore.App 2.2.0 requires Microsoft.EntityFrameworkCore.SqlServer (>= 2.2.0 && < 2.3.0) but version Microsoft.EntityFrameworkCore.SqlServer 3.1.2 was resolved.

projectname-> projectname.BusinessLogic -> projectname.DataAccess -> Microsoft.EntityFrameworkCore (>= 3.1.2) 
 projectname-> Microsoft.AspNetCore.App 2.2.0 -> Microsoft.EntityFrameworkCore (>= 2.2.0 && < 2.3.0).

我在上个中午试图解决这个错误，但错误没有解决

请帮忙？

Answer 1

安装nuget包：

Install-Package Microsoft.EntityFrameworkCore.SqlServer

并将这个指令放在你的类中：

using Microsoft.EntityFrameworkCore;

没有指令或 nuget 包它不起作用

Answer 2

安装 nuget 包

Install-Package Microsoft.EntityFrameworkCore.SqlServer