Microsoft.EntityFrameworkCore.SqlServer依赖关系无法解决

Question

I am trying to install Entity Framework Core in VS 2015, Update 3, so I can reverse-engineer EF models from an existing database. I am following the directions from Microsoft, here: https://docs.microsoft.com/en-us/ef/core/get-started/aspnetcore/existing-db .

However, as soon as this line is added to my project.json file:

    "Microsoft.EntityFrameworkCore.SqlServer":  "1.1.0" 

I get a "Package restore failed" error in my References, saying the dependency could not be resolved. I get this same error no matter what version I specify.

Below is the full content of my package.json file - the only line I added is the one mentioned above. All the rest are there by default when I create the project from the "New ASP.NET Core Web Application" template.

I have tried adding a reference to Microsoft.EntityFrameworkCore, as suggested here: How to resolve the dependency on Microsoft.EntityFrameworkCore.SqlServer and Microsoft.EntityFrameworkCore.Tools? , but I get the same error message with regard to that reference (again, no matter what version I specify).

Can anyone explain what the problem is, and how a person is supposed to be able to figure this out from the minimal information provided?

{
    "dependencies": {
        "Microsoft.NETCore.App": {
            "version": "1.0.1",
            "type": "platform"
        },
        "Microsoft.ApplicationInsights.AspNetCore": "1.0.0",
        "Microsoft.AspNetCore.Diagnostics": "1.0.0",
        "Microsoft.AspNetCore.Mvc": "1.0.1",
        "Microsoft.AspNetCore.Razor.Tools": {
            "version": "1.0.0-preview2-final",
            "type": "build"
        },
        "Microsoft.AspNetCore.Routing": "1.0.1",
        "Microsoft.AspNetCore.Server.IISIntegration": "1.0.0",
        "Microsoft.AspNetCore.Server.Kestrel": "1.0.1",
        "Microsoft.AspNetCore.StaticFiles": "1.0.0",
        "Microsoft.Extensions.Configuration.EnvironmentVariables": "1.0.0",
        "Microsoft.Extensions.Configuration.Json": "1.0.0",
        "Microsoft.Extensions.Logging": "1.0.0",
        "Microsoft.Extensions.Logging.Console": "1.0.0",
        "Microsoft.Extensions.Logging.Debug": "1.0.0",
        "Microsoft.Extensions.Options.ConfigurationExtensions": "1.0.0",
        "Microsoft.VisualStudio.Web.BrowserLink.Loader": "14.0.0",
        "Microsoft.EntityFrameworkCore.SqlServer":  "1.1.0"
    },

  "tools": {
    "BundlerMinifier.Core": "2.0.238",
    "Microsoft.AspNetCore.Razor.Tools": "1.0.0-preview2-final",
    "Microsoft.AspNetCore.Server.IISIntegration.Tools": "1.0.0-preview2-final"
  },

  "frameworks": {
    "netcoreapp1.0": {
      "imports": [
        "dotnet5.6",
        "portable-net45+win8"
      ]
    }
  },

  "buildOptions": {
    "emitEntryPoint": true,
    "preserveCompilationContext": true
  },

  "runtimeOptions": {
    "configProperties": {
      "System.GC.Server": true
    }
  },

  "publishOptions": {
    "include": [
      "wwwroot",
      "**/*.cshtml",
      "appsettings.json",
      "web.config"
    ]
  },

  "scripts": {
    "prepublish": [ "bower install", "dotnet bundle" ],
    "postpublish": [ "dotnet publish-iis --publish-folder %publish:OutputPath% --framework %publish:FullTargetFramework%" ]
  }
}

Answer 1

Turns out the problem for me was an invalid package source. I removed the invalid source in the NuGet Package Manager, and I was then able to add the reference.