找不到适合实体类型 MyImage 的构造函数

Question

我收到此异常：

System.InvalidOperationException HResult=0x80131509 消息=找不到适合实体类型“MyImage”的构造函数。以下构造函数的参数无法绑定到实体类型的属性：无法在“MyImage(string name, string country, Image image)”中绑定“image”。Source=Microsoft.EntityFrameworkCore StackTrace：在 Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.ConstructorBindingConvention.Apply(InternalModelBuilder modelBuilder) 在 Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.ConventionDispatcher.ImmediateConventionFrame.OnModelBuilt(InternalModelBuilder modelBuilder) 在 Microsoft.Core Microsoft.EntityFrameworkCore 中的 Metadata.Conventions.Internal.ConventionDispatcher.OnModelBuilt(InternalModelBuilder modelBuilder)。1.ViaFactory(LazyThreadSafetyMode mode) at System.Lazy1.ExecutionAndPublication(LazyHelper executionAndPublication, Boolean useDefaultConstructor) at System.Lazy 1.CreateValue() at Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.GetModel(DbContext context, IConventionSetBuilder conventionSetBuilder, IModelValidator validator) at Microsoft.EntityFrameworkCore.Internal.DbContextServices.CreateModel() at Microsoft.EntityFrameworkCore.Internal.DbContextServices.get_Model() at Microsoft.EntityFrameworkCore.Infrastructure.EntityFrameworkServicesBuilder.<>c.<TryAddCoreServices>b__7_2(IServiceProvider p) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactory(FactoryCallSite factoryCallSite, ServiceProviderEngineScope scope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor2.VisitCallSite(IServiceCallSite callSite, TArgument argument) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitRuntimeResolver.VisitScopes.VisitScoped. ServiceLookup.CallSiteVisitor 2.VisitCallSite(IServiceCallSite callSite, TArgument argument) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitConstructor(ConstructorCallSite constructorCallSite, ServiceProviderEngineScope scope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor2.VisitCallSite(IServiceCallSite callSite, TArgument argument) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped(ScopedCallSite scopedCallSite, ServiceProviderEngineScope scope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped(ScopedCallSite scopedCallSite, ServiceProviderEngineScopescope) at Microsoft.Extensions.VisitorLjectionLjectionCallendS2.VisitCallSite(IServiceCallSite callSite, TArgument argument) at Microsoft.Extensions.DependencyInjection.ServiceLookup.DynamicServiceProviderEngine.<>c__DisplayClass1_0.<RealizeService>b__0(ServiceProviderEngineScope scope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngine.GetService(Type serviceType, ServiceProviderEngineScope serviceProviderEngineScope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope.GetService(Type serviceType) at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType) at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService[T](IServiceProvider provider) at Microsoft.EntityFrameworkCore.DbContext.get_DbContextDependencies() at Microsoft.EntityFrameworkCore.DbContext.get_InternalServiceProvider() at Microsoft.EntityFrameworkCore.DbContext.Microsoft.EntityFrameworkCore.Infrastructure.IInfrastructure<System.IServiceProvider>.get_Instance() at Microsoft.EntityFrameworkCore.Infrastructure.DatabaseFacade.Microsoft.EntityFrameworkCore.Infrastructure.IInfrastructure<System.IServiceProvider>.get_Instance() at Microsoft.EntityFrameworkCore.Internal.InternalAccessorExtensions.GetService[TService](IInfrastructure1 个访问器）在 Microsoft.EntityFrameworkCore.Infrastructure.AccessorExtensions.GetService[TService]（IInfrastructure`1 访问器）在 Microsoft.EntityFrameworkCore.Infrastructure.DatabaseFacade.get_DatabaseCreator() 在 Microsoft.EntityFrameworkCore.Infrastructure.DatabaseFacade.EnsureDeleted() 在 DigitizedApi. .DataInitializer.InitializeData() in D:\School\Webapplicaties IV\DigitizedApi\DigitizedApi\DigitizedApi\Data\DataInitializer.cs：第 27 行 DigitizedApi.Startup.Configure(IApplicationBuilder app, IHostingEnvironment env, DataInitializer dataInitializer) in D \Webappplicaties IV\DigitizedApi\DigitizedApi\DigitizedApi\Startup.cs:line 103

我不知道原因可能是什么。

数据库上下文

    public class ApplicationDbContext : IdentityDbContext {

    public DbSet<MyImage> Images { get; set; }
    public DbSet<Visitor> Visitors { get; set; }

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

    protected override void OnModelCreating(ModelBuilder builder) {
        base.OnModelCreating(builder);
        builder.ApplyConfiguration(new ImageConfiguration());
        builder.ApplyConfiguration(new VisitorConfiguration());
        builder.ApplyConfiguration(new ImageVisitorConfiguration());
    }
}

数据初始化器

        private readonly ApplicationDbContext _dbContext;
    private readonly UserManager<IdentityUser> _userManager;
    private readonly IImageRepository _imageRepository;

    public DataInitializer(ApplicationDbContext context, UserManager<IdentityUser> userManager, IImageRepository imageRepository) {
        _dbContext = context;
        _userManager = userManager;
        _imageRepository = imageRepository;
    }

    //public async Task InitializeData() {
    //    _dbContext.Database.EnsureDeleted();
    //    if (_dbContext.Database.EnsureCreated()) {
    //    }
    //}

    public void InitializeData() {
        _dbContext.Database.EnsureDeleted();//error gets thrown here
        if (_dbContext.Database.EnsureCreated()) {
            //MyImage image1 = new MyImage("Parallax1","France",Image.FromFile("DSC_2544c2.jpg"));
            //_imageRepository.Add(image1);

            _imageRepository.SaveChanges();



        }
    }

    private async Task CreateUser(string email, string password) {
        var user = new IdentityUser { UserName = email, Email = email };
        await _userManager.CreateAsync(user, password);
    }
}

MyImage 类

    public class MyImage {

    #region Fields
    private string _name;
    #endregion

    #region Properties
    public int Id { get; set; }
    [Required]
    public string Name {
        get {
            return _name;
        }

        set {
            if (string.IsNullOrEmpty(value) || string.IsNullOrWhiteSpace(value)) {
                throw new ArgumentException("Name cannot be empty.");
            }
            _name = value;
        }
    }
    public int ISO { get; set; }
    public double ShutterSpeed { get; set; }
    public double Aperture { get; set; }
    public string Country { get; set; }
    public string Content { get; set; }
    #endregion

    #region Constructor
    //public MyImage(string name, int iso, double shutterspeed, double aperture, string country, string content) {
    //    Name = name;
    //    ISO = iso;
    //    ShutterSpeed = shutterspeed;
    //    Aperture = aperture;
    //    Country = country;
    //    Content = content;

    //}

    public MyImage(string name, string country, Image image) {
        Name = name;
        ISO = Convert.ToInt32(Encoding.UTF8.GetString(image.GetPropertyItem(0x8828).Value));
        ShutterSpeed = Convert.ToInt64(Encoding.UTF8.GetString(image.GetPropertyItem(0x9201).Value));
        Aperture = Convert.ToInt32(Encoding.UTF8.GetString(image.GetPropertyItem(0x9202).Value)); ;
        Country = country;
        Content = ConvertImage(image);

    }
    #endregion

    #region Methods
    private string ConvertImage(Image imageToConvert) {
        byte[] Ret;
        try {
            using (MemoryStream ms = new MemoryStream()) {
                imageToConvert.Save(ms, imageToConvert.RawFormat);
                Ret = ms.ToArray();
            }
        } catch (Exception ex) {
            throw;
        }
        return Convert.ToBase64String(Ret);
    }
    #endregion
}

配置

    public class ImageConfiguration : IEntityTypeConfiguration<MyImage> {
    public void Configure(EntityTypeBuilder<MyImage> builder) {
        builder.ToTable("Image");

        builder.HasKey(i => i.Id);

        builder.Property(i => i.Name)
            .HasMaxLength(40)
            .IsRequired(true);

        builder.Property(i => i.Country)
            .HasMaxLength(84)
            .IsRequired(true);

        builder.Property(i => i.Content)
            .IsRequired(true);
    }
}

访客类

    public class Visitor {

    #region Fields
    private string _name;
    private string _email;
    private string _telephone;
    #endregion

    #region Properties
    public int Id { get; set; }
    public string Name {
        get {
            return _name;
        }
        set {
            if (string.IsNullOrEmpty(value) || string.IsNullOrWhiteSpace(value)) {
                throw new ArgumentException("Name can't be empty.");
            }
            _name = value;
        }
    }

    public string Email {
        get {
            return _email;
        }
        set {
            if (string.IsNullOrEmpty(value) || string.IsNullOrWhiteSpace(value)) {
                throw new ArgumentException("Email can't be empty.");
            }
            Regex regex = new Regex(@"^([a-zA-Z0-9éèà]+[a-zA-Z0-9.-éèàïëöüäîôûêâù]*)@([a-zA-Z]+)[.]([a-z]+)([.][a-z]+)*$");
            Match match = regex.Match(value);
            if (!match.Success) {
                throw new ArgumentException("Email doesn't have a correct format.");
            }
            _email = value;
        }
    }

    public string Telephone {
        get {
            return _telephone;
        }
        set {
            if (string.IsNullOrEmpty(value) || string.IsNullOrWhiteSpace(value)) {
                throw new ArgumentException("Telephone number can't be empty.");
            }
            Regex regex = new Regex(@"(\+(0)?|00)(9[976]\d|8[987530]\d|6[987]\d|5[90]\d|42\d|3[875]\d|2[98654321]\d|9[8543210]|8[6421]|6[6543210]|5[87654321]|4[987654310]|3[9643210]|2[70]|7|1)\d{1,14}$");
            Match match = regex.Match(value);
            if (!match.Success) {
                throw new ArgumentException("Telephone number doesn't have a correct format. " +
                    "Please make sure you use an international phone number (+44791112345) and dont forget to add the +.");
            }
            _telephone = value;
        }
    }

    public string Country { get; set; }

    public ICollection<LikedImage> Liked { get; private set; }
    public IEnumerable<MyImage> LikedImages => Liked.Select(i => i.Image);
    #endregion

    #region Constructor
    public Visitor(string name, string email, string telephone, string country = null) {
        Name = name;
        Email = email;
        Telephone = telephone;
        Country = country;
    }
    #endregion
}

访客配置

public class VisitorConfiguration : IEntityTypeConfiguration<Visitor> {
    public void Configure(EntityTypeBuilder<Visitor> builder) {
        builder.ToTable("Visitors");

        builder.HasKey(v => v.Id);

        builder.Property(v => v.Name)
            .HasMaxLength(50)
            .IsRequired(true);

        builder.Property(v => v.Email)
            .HasMaxLength(70)
            .IsRequired(true);

        builder.Property(v => v.Telephone)
            .HasMaxLength(15)
            .IsRequired(true);
    }
}

交点表

   public class LikedImage {
    #region Properties
    public int ImageId { get; set; }

    public int VisitorId { get; set; }

    public Visitor Visitor { get; set; }

    public MyImage Image { get; set; }
    #endregion
}

它的配置

    public class ImageVisitorConfiguration : IEntityTypeConfiguration<LikedImage> {
    public void Configure(EntityTypeBuilder<LikedImage> builder) {
        builder.HasKey(i => new { i.ImageId, i.VisitorId });

        builder.HasOne(i => i.Visitor)
            .WithMany(v => v.Liked)
            .HasForeignKey(i => i.VisitorId);

        builder.HasOne(i => i.Image)
            .WithMany()
            .HasForeignKey(i => i.ImageId);
    }
}

最后

启动

    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.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);

        services.AddDbContext<ApplicationDbContext>(options =>
          options.UseSqlServer(Configuration.GetConnectionString("DigitizedContext")));

        services.AddScoped<DataInitializer>();
        services.AddScoped<IImageRepository, ImageRepository>();
        services.AddScoped<IVisitorRepository, VisitorRepository>();

        services.AddOpenApiDocument(c => {
            c.DocumentName = "apidocs";
            c.Title = "DigitizedAPI";
            c.Version = "v1";
            c.Description = "The DigitizedAPI documentation description.";
            c.DocumentProcessors.Add(new SecurityDefinitionAppender("JWT Token", new SwaggerSecurityScheme {
                Type = SwaggerSecuritySchemeType.ApiKey,
                Name = "Authorization",
                In = SwaggerSecurityApiKeyLocation.Header,
                Description = "Copy 'Bearer' + valid JWT token into field"
            }));
            c.OperationProcessors.Add(new OperationSecurityScopeProcessor("JWT Token"));
        });

        services.AddIdentity<IdentityUser, IdentityRole>(cfg => cfg.User.RequireUniqueEmail = true).AddEntityFrameworkStores<ApplicationDbContext>();
        services.Configure<IdentityOptions>(options => {

            options.Lockout.DefaultLockoutTimeSpan = TimeSpan.FromMinutes(5);
            options.Lockout.MaxFailedAccessAttempts = 3;
            options.Lockout.AllowedForNewUsers = true;

            options.User.AllowedUserNameCharacters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890-._@+";
            options.User.RequireUniqueEmail = true;
        });

        services.AddAuthentication(x => {
            x.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
        }).AddJwtBearer(x => {
            x.RequireHttpsMetadata = false;
            x.SaveToken = true;
            x.TokenValidationParameters = new TokenValidationParameters {
                ValidateIssuerSigningKey = true,
                IssuerSigningKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(Configuration["Tokens:Key"])),
                ValidateIssuer = false,
                ValidateAudience = false,
                RequireExpirationTime = true
            };
        });

        //change later to the origen of my site
        services.AddCors(options =>
    options.AddPolicy("AllowAllOrigins", builder => builder.AllowAnyOrigin()
));
    }

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

        app.UseMvc();

        app.UseSwaggerUi3();
        app.UseSwagger();

        app.UseCors("AllowAllOrigins");

        //dataInitializer.InitializeData().Wait();
        dataInitializer.InitializeData();
    }
}

非常抱歉，我知道代码很多，但我是一名学生，我的老师有点抛弃了我们，我们需要自己找出问题所在，我不知道哪里出了问题。

提前致谢！

Answer 1

EF.Core 在内部调用实体构造函数，因此 EF.Core 应该以某种方式确定要作为参数传递的内容。EF.Core < 2.1 根本无法注入参数，但从 EF.Core 2.1 开始是可能的 - 如果所有参数与属性具有相同的名称，EF.Core 使用属性值作为参数值（有关更多信息，请参阅文档)：

从 EF Core 2.1 开始，现在可以定义带参数的构造函数，并让 EF Core 在创建实体实例时调用此构造函数。构造函数参数可以绑定到映射属性或各种服务，以促进延迟加载等行为。

在您的情况下，无法解析Image image参数（EF.Core 2.1，旧的 EF.Core 根本不起作用），因此简单的解决方案是向您的MyImage类添加默认构造函数。

Answer 2

我修复了在模型中添加默认构造函数的问题，进入 MyImage 文件类并添加：

public MyImage(){}