值不能为空 - 内存数据库.Net答案

【问题标题】：Value cannot be null - In-Memory Database .Net值不能为空 - 内存数据库.Net
【发布时间】：2022-01-03 16:35:26
【问题描述】：

我正在尝试使用内存数据库，但收到以下消息：

System.ArgumentNullException: '值不能为空。（范围 '来源'）'

我阅读了很多与此问题相关的类似问题，但每篇文章都与连接字符串有关，我认为我不能使用连接字符串，因为它是内存数据库。我做错了什么？我留下我的代码：

DbInitializer.cs - 在这个类中出现错误

public static class DbInitializer
{
    public static void Initialize(IServiceProvider serviceProvider)
    {
        using (var _context = new AppDBContext(serviceProvider.GetRequiredService<DbContextOptions<AppDBContext>>()))
        {
            if (_context.AgentsRole.Any()) //In this line appears the error
                return;
            _context.AgentsRole.AddRange(
                    new Agent { Id = 1, Role_Name = "David Lopez", Is_Active = true, Role_Description = "This is a test for David Lopez" },
                    new Agent { Id = 2, Role_Name = "James Norris", Is_Active = false, Role_Description = "This is a test for James Norris" },
                    new Agent { Id = 3, Role_Name = "Jhon Norris", Is_Active = true, Role_Description = "This is a test for Jhon Norris" },
                    new Agent { Id = 4, Role_Name = "James Norr", Is_Active = true, Role_Description = "This is a test for James Norr" }
                );
            _context.SaveChanges();
        }
    }
}

Startup.cs:

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

        public IConfiguration Configuration { get; }

        public void ConfigureServices(IServiceCollection services)
        {
            services.AddDbContext<AppDBContext>(options=> options.UseInMemoryDatabase(databaseName: "InMemory_DB"));
            services.AddControllers();
            services.AddSwaggerGen();
        }

        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.UseHttpsRedirection();

            app.UseRouting();

            app.UseAuthorization();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllers();
            });
            app.UseSwagger();
            app.UseSwaggerUI(c =>
            {
                c.SwaggerEndpoint("/swagger/v1/swagger.json", "My Test1 Api v1");
            });
        }
    }

Program.cs:

public class Program
    {
        public static void Main(string[] args)
        {
            var host = CreateHostBuilder(args).Build();

            using (var scope = host.Services.CreateScope())
            {
                var services = scope.ServiceProvider;
                var context = services.GetRequiredService<AppDBContext>();
                DbInitializer.Initialize(services);
            }
            host.Run();
        }

        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                });
    }

Controller.cs:

[ApiController]
[Route("api/[controller]")]
public class AgentRoleController : ControllerBase
{
    private readonly ILogger<AgentRoleController> _logger;
    private readonly AppDBContext _context;
    public AgentRoleController(ILogger<AgentRoleController> logger, AppDBContext context)
    {
        _logger = logger;
        _context = context;
    }
    [HttpGet]
    [SwaggerOperation("GetAgentsRole")]
    [SwaggerResponse((int)HttpStatusCode.OK)]
    [SwaggerResponse((int)HttpStatusCode.NotFound)]
    public IEnumerable<Agent> Get()
    {
        return _context.AgentsRole;
    }
}

AppDBContext.cs:

public class AppDBContext : DbContext
{
    public AppDBContext(DbContextOptions<AppDBContext> options)
        :base(options)
    {
       
    }
    public DbSet<Agent> AgentsRole;
}

【问题讨论】：

public DbSet<Agent> AgentsRole; 在什么时候初始化？我在任何地方都看不到。如果它没有初始化，你会得到一个异常
您需要做的不仅仅是“多读”。你需要fix it。
@Charlieface 当我询问对象是否退出 DBInitializer 时，我初始化了 AgentsRole，在该行中出现错误，如果答案为 false，它将值添加到表和 AgentsRole 将不会空的，不是吗？
_context.AgentsRole.Any() 不会初始化它，您需要实际创建一个对象并将其存储在该变量中。请注意，@DourHighArch 上面的链接也有助于ArgumentNullException

标签： sql .net entity-framework in-memory-database

【解决方案1】：

解决方法在AppDBContext.cs中，我错过了AgentsRole的初始化，解决方法是：

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

    }
    public DbSet<Agent> AgentsRole { get; set; } // I added this Part!
}

【讨论】：