c# - Entity Framework 核心 : Cannot add migrations: No parameterless constructor

Question

我的数据项目引用:(Entity Framework Core)

    <Project Sdk="Microsoft.NET.Sdk">    
      <PropertyGroup>
        <TargetFramework>netcoreapp1.1</TargetFramework>
      </PropertyGroup>    
      <ItemGroup>
        <PackageReference Include="Microsoft.AspNetCore.Identity.EntityFrameworkCore" Version="1.1.1" />
        <ProjectReference Include="..\Butv.Core\Butv.Core.csproj" />
        <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="1.0.3" />
<PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer.Design" Version="1.1.1" PrivateAssets="All" />      
        <PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="1.0.0" />    
      </ItemGroup>
      <ItemGroup>
        <DotNetCliToolReference Include="Microsoft.EntityFrameworkCore.Tools.DotNet" Version="1.0.0" />  
      </ItemGroup>
      <ItemGroup>
        <Folder Include="Migrations\" />
      </ItemGroup>
    </Project>

数据库上下文:

public class ApplicationDbContext : IdentityDbContext<ApplicationUser>
{
     public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options) : base(options) { }

     protected override void OnModelCreating(ModelBuilder modelBuilder)
     {  ....
     }
}
public class ApplicationUser : IdentityUser
{
}

每次我尝试命令

dotnet ef migrations add Init --verbose

，我得到了错误。在我将数据项目与主项目分开之前，它曾经工作得很好。

Microsoft.EntityFrameworkCore.Design.OperationException: No parameterless constr uctor was found on 'ApplicationDbContext'. Either add a parameterless constructo r to 'ApplicationDbContext' or add an implementation of 'IDbContextFactory' in the same assembly as 'ApplicationDbContext'. ---> System.Mi ssingMethodException: No parameterless constructor defined for this object. at System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOn ly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandleInternal& ctor, Bo olean& bNeedSecurityCheck)

Answer 1

我遇到了同样的问题。我已经在正常迁移的项目上得到了它。从某个时候开始，它开始给我这个错误。问题出在启动项目 选择中。选择一个项目作为启动项目，您在其中将 Entity Framework 配置为用作服务。

This can help