进行添加迁移时，EntityFramework核心模型关系问题

Question

在asp.net核心项目中使用Package Manager Console进行迁移时，我遇到EntityFramework核心模型关系问题。

添加迁移“添加迁移”时遇到错误。

无法确定由类型为“ ICollection”的导航属性“ College.Users”表示的关系。 手动配置关系，或从模型中忽略此属性。

完全错误

System.InvalidOperationException：无法确定类型为“ ICollection”的导航属性“ College.Users”表示的关系。 手动配置关系，或从模型中忽略此属性。 位于Microsoft.EntityFrameworkCore.Metadata.Context（Model.Context.Model.Context.Context。 Microsoft.EntityFrameworkCore.Internal.DbContextServices.CreateModel 2.GetOrAdd(TKey key, Func ）处的System.Collections.Concurrent.ConcurrentDictionary 2.GetOrAdd(TKey key, Func 2 valueFactory）的IConventionSetBuilder ConventionSetBuilder，IModelValidator验证器）Microsoft.EntityFrameworkCore.Internal.LazyRef 1.get_Value() at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped(ScopedCallSite scopedCallSite, ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceProvider.<>c__DisplayClass16_0.<RealizeService>b__0(ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetService[T](IServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitTransient(TransientCallSite transientCallSite, ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitConstructor(ConstructorCallSite constructorCallSite, ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitTransient(TransientCallSite transientCallSite, ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceProvider.<>c__DisplayClass16_0.<RealizeService>b__0(ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType) at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService[T](IServiceProvider provider) at Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations.AddMigration(String name, String outputDir, String contextType) at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigrationImpl(String name, String outputDir, String contextType) at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.<>c__DisplayClass3_0 1.get_Value() at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped(ScopedCallSite scopedCallSite, ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceProvider.<>c__DisplayClass16_0.<RealizeService>b__0(ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetService[T](IServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitTransient(TransientCallSite transientCallSite, ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitConstructor(ConstructorCallSite constructorCallSite, ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitTransient(TransientCallSite transientCallSite, ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceProvider.<>c__DisplayClass16_0.<RealizeService>b__0(ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType) at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService[T](IServiceProvider provider) at Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations.AddMigration(String name, String outputDir, String contextType) at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigrationImpl(String name, String outputDir, String contextType) at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.<>c__DisplayClass3_0 1.get_Value() at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped(ScopedCallSite scopedCallSite, ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceProvider.<>c__DisplayClass16_0.<RealizeService>b__0(ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetService[T](IServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitTransient(TransientCallSite transientCallSite, ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitConstructor(ConstructorCallSite constructorCallSite, ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitTransient(TransientCallSite transientCallSite, ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceProvider.<>c__DisplayClass16_0.<RealizeService>b__0(ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType) at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService[T](IServiceProvider provider) at Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations.AddMigration(String name, String outputDir, String contextType) at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigrationImpl(String name, String outputDir, String contextType) at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.<>c__DisplayClass3_0 1.b__0 （），位于Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute（Action action）无法确定由类型为“ ICollection”的导航属性“ College.Users”表示的关系。 手动配置关系，或从模型中忽略此属性。

我有以下型号

public class College
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    [JsonProperty("id")]
    public int Id { get; set; }

    [JsonProperty("name")]
    public string CollegeName { get; set; }

    [ForeignKey("Users")]
    [JsonProperty("users")]
    public ICollection<User> Users { get; set; }
}

public class User
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    [JsonProperty("id")]
    public int Id { get; set; }

    [JsonProperty("name")]
    public string UserName { get; set; }

    [JsonProperty("email")]
    public string UserEmail { get; set; }

    [JsonProperty("phone")]
    public string UserPhone { get; set; }

    [ForeignKey("CollegeId")]
    [JsonProperty("college")]
    public College College{ get; set; }
}

请任何人对此问题有所了解。

谢谢

Answer 1

简短答案：您错误地使用了ForeignKey属性。 删除它，您的迁移应开始工作：

public class College
{
    public int Id { get; set; }
    public string CollegeName { get; set; }
    public ICollection<User> Users { get; set; }
}

public class User
{
    public int Id { get; set; }
    public string UserName { get; set; }
    public string UserEmail { get; set; }
    public string UserPhone { get; set; }
    public College College{ get; set; }
}

长答案：在您的示例中，您将在模型上忽略外键ID属性。 相反，您仅包括navigation属性。 按照约定，您可以通过将外键属性命名为与您所引用的类相同的名称并在末尾添加一个ID来包含外键属性。 在您的示例中将是：

public int CollegeId {get;set;}

如果您不想遵循此约定，则可以使用ForeignKeyAttribute。 例如，假设您想命名属性PrimaryCollegeId。 您可以这样使用ForeignKeyAttribute来做到这一点：

public int PrimaryCollegeId {get;set;}
[ForeignKey("PrimaryCollegeId")]
public College College {get;set;}

如果在同一张表之间有多个关系，通常会使用ForeignKeyAttribute。 例如，如果学生同时拥有一所小学和中学作为外键。