CS0311 C# 该类型不能用作泛型类型或方法中的类型参数“TContext”。实体框架核心

Question

我指定了我在 Startup.cs 文件的实体项目中创建的上下文类和我为 connectionString 创建的 connectionString 数据。但是为什么我会收到这个错误？

错误消息：严重性代码描述项目文件行抑制状态错误 CS0311 类型“Microsoft.ApplicationInsights.Extensibility.Implementation.UserContext”不能用作泛型类型或方法“EntityFrameworkServiceCollectionExtensions.AddDbContext(IServiceCollection, Action, ServiceLifetime, ServiceLifetime)'。没有从“Microsoft.ApplicationInsights.Extensibility.Implementation.UserContext”到“Microsoft.EntityFrameworkCore.DbContext”的隐式引用转换。EntityFramework2 C:\Users\xsamu\source\repos\EntityFramework2\EntityFramework2\Startup.cs 29 活动

启动类：

namespace EntityFramework2
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllersWithViews();
            services.AddDbContext<UserContext>(options => options.UseSqlServer(Configuration.GetConnectionString("DevConnection")));
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Home/Error");
                // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
                app.UseHsts();
            }
            app.UseHttpsRedirection();
            app.UseStaticFiles();

            app.UseRouting();

            app.UseAuthorization();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllerRoute(
                    name: "default",
                    pattern: "{controller=Home}/{action=Index}/{id?}");
            });
        }
    }
}

实体配置：

namespace EntityFramework2
{
    public class EntityConfiguration : IEntityTypeConfiguration<User>
    {
        public void Configure(EntityTypeBuilder<User> builder)
        {
            builder.HasOne<Department>(navigationExpression: s => s.Name)
                .WithOne(sa => sa.User)
                .HasForeignKey<Department>(sa => sa.DepartmentId);

            builder.HasOne<Title>(navigationExpression: s => s.TitleCode)
               .WithOne(sa => sa.User)
               .HasForeignKey<Title>(sa => sa.TitleId);

            builder.HasOne<Position>(navigationExpression: s => s.PositionCode)
               .WithOne(sa => sa.User)
               .HasForeignKey<Position>(sa => sa.PositionId);
        }
    }
}

Answer 1

没有从“Microsoft.ApplicationInsights.Extensibility.Implementation.UserContext”到“Microsoft.EntityFrameworkCore.DbContext”的隐式引用转换。

该消息告诉您，您的UserContext类不继承自DbContext，这是强制性的。

它应该是这样的：

public class BloggingContext : DbContext
{
    public BloggingContext(DbContextOptions<BloggingContext> options)
        : base(options)
    { }

    public DbSet<Blog> Blogs { get; set; }
}

有关更多信息，请参阅EF Core 教程和配置 DbContext。