EF Core 中的枚举列表

问题描述 投票：0回答：4

是否可以在使用 EF Core 的项目中使用枚举列表来存储数据？

我的枚举：

   public enum AudienceType
    {
        Child,
        Teen,
        [Display(Name ="Young Adult")]
        YoungAdult,
        Adult,
        Elderly
    }

使用枚举的类：

public class Restaurant
{
    public int Id { get; set; }
    [Required, StringLength(80)]
    public string Name { get; set; }
    [Display(Name="Select the target audiences")]
    public List<AudienceType> AudienceTypes { get; set; }
}

但是当我运行

add-migration AudienceType
时，我收到以下错误：

PM> add-migration AudienceType
Build started...
Build succeeded.
System.InvalidOperationException: The property 'Restaurant.AudienceTypes' could not be mapped, because it is of type 'List<AudienceType>' which is not a supported primitive type or a valid entity type. Either explicitly map this property, or ignore it using the '[NotMapped]' attribute or by using 'EntityTypeBuilder.Ignore' in 'OnModelCreating'.
   at Microsoft.EntityFrameworkCore.Infrastructure.ModelValidator.ValidatePropertyMapping(IModel model, IDiagnosticsLogger`1 logger)
   at Microsoft.EntityFrameworkCore.Infrastructure.ModelValidator.Validate(IModel model, IDiagnosticsLogger`1 logger)
   at Microsoft.EntityFrameworkCore.Infrastructure.RelationalModelValidator.Validate(IModel model, IDiagnosticsLogger`1 logger)
   at Microsoft.EntityFrameworkCore.SqlServer.Internal.SqlServerModelValidator.Validate(IModel model, IDiagnosticsLogger`1 logger)
   at Microsoft.EntityFrameworkCore.Metadata.Conventions.ValidatingConvention.ProcessModelFinalized(IConventionModelBuilder modelBuilder, IConventionContext`1 context)
   at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.ConventionDispatcher.ImmediateConventionScope.OnModelFinalized(IConventionModelBuilder modelBuilder)
   at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.ConventionDispatcher.OnModelFinalized(IConventionModelBuilder modelBuilder)
   at Microsoft.EntityFrameworkCore.Metadata.Internal.Model.FinalizeModel()
   at Microsoft.EntityFrameworkCore.ModelBuilder.FinalizeModel()
   at Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.CreateModel(DbContext context, IConventionSetBuilder conventionSetBuilder)
   at Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.GetModel(DbContext context, IConventionSetBuilder conventionSetBuilder)
   at Microsoft.EntityFrameworkCore.Internal.DbContextServices.CreateModel()
   at Microsoft.EntityFrameworkCore.Internal.DbContextServices.get_Model()
   at Microsoft.EntityFrameworkCore.Infrastructure.EntityFrameworkServicesBuilder.<>c.<TryAddCoreServices>b__7_3(IServiceProvider p)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactory(FactoryCallSite factoryCallSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSiteMain(ServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitCache(ServiceCallSite callSite, RuntimeResolverContext context, ServiceProviderEngineScope serviceProviderEngine, RuntimeResolverLock lockType)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScopeCache(ServiceCallSite singletonCallSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(ServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitConstructor(ConstructorCallSite constructorCallSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSiteMain(ServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitCache(ServiceCallSite callSite, RuntimeResolverContext context, ServiceProviderEngineScope serviceProviderEngine, RuntimeResolverLock lockType)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScopeCache(ServiceCallSite singletonCallSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(ServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.Resolve(ServiceCallSite callSite, ServiceProviderEngineScope scope)
   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.Internal.InfrastructureExtensions.GetService[TService](IInfrastructure`1 accessor)
   at Microsoft.EntityFrameworkCore.Infrastructure.AccessorExtensions.GetService[TService](IInfrastructure`1 accessor)
   at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext(Func`1 factory)
   at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext(String contextType)
   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.AddMigration.<>c__DisplayClass0_0.<.ctor>b__0()
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.<>c__DisplayClass3_0`1.<Execute>b__0()
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)
The property 'Restaurant.AudienceTypes' could not be mapped, because it is of type 'List<AudienceType>' which is not a supported primitive type or a valid entity type. Either explicitly map this property, or ignore it using the '[NotMapped]' attribute or by using 'EntityTypeBuilder.Ignore' in 'OnModelCreating'.

更新： 我了解如何使用值转换来处理枚举，如下所示：

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    base.OnModelCreating(modelBuilder);

    var converter = new EnumToStringConverter<AudienceType>();

    modelBuilder
        .Entity<Restaurant>()
        .Property(e => e.AudienceTypes)
        .HasConversion(converter);
}

但是如何处理枚举列表？

list asp.net-core enums ef-core-3.1
4个回答
5
投票

要将枚举值列表表示为逗号分隔的字符串，您可以使用值转换。

最简单的“内联”选项：

// In DbContext class
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
  modelBuilder
      .Entity<Restaurant>()
      .Property(e => e.AudienceTypes)
      .HasConversion(
          v => string.Join(",", v.Select(e => e.ToString("D")).ToArray()),
          v => v.Split(new[] { ',' })
            .Select(e =>  Enum.Parse(typeof(AudienceType), e))
            .Cast<AudienceType>()
            .ToList()
      );
}
3
投票

我发现这篇文章很有帮助，这导致了以下解决方案：

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);

        var converter = new EnumCollectionJsonValueConverter<AudienceType>();
        var comparer = new CollectionValueComparer<AudienceType>();

        modelBuilder.Entity<Restaurant>()
          .Property(e => e.AudienceTypes)
          .HasConversion(converter)
          .Metadata.SetValueComparer(comparer);
   }

它使用以下两个类：

public class EnumCollectionJsonValueConverter<T> : ValueConverter<ICollection<T>, string> where T : Enum
{
    public EnumCollectionJsonValueConverter() : base(
      v => JsonConvert
        .SerializeObject(v.Select(e => e.ToString()).ToList()),
      v => JsonConvert
        .DeserializeObject<ICollection<string>>(v)
        .Select(e => (T)Enum.Parse(typeof(T), e)).ToList())
    {
    }
   }

public class CollectionValueComparer<T> : ValueComparer<ICollection<T>>
{
    public CollectionValueComparer() : base((c1, c2) => c1.SequenceEqual(c2),
      c => c.Aggregate(0, (a, v) => HashCode.Combine(a, v.GetHashCode())), c => (ICollection<T>)c.ToHashSet())
    {
    }
}
0
投票

因为enum不是类，所以需要自己写一个新的类来封装它。

您可以创建一个新班级：

public class Audience
{
    public int Id { get; set; }
    public AudienceType AudienceType { get; set; }
}

然后在你的

Restaurant
：

    public class Restaurant
{
    public int Id { get; set; }
    [Required, StringLength(80)]
    public string Name { get; set; }
    [Display(Name="Select the target audiences")]
    public List<Audience> Audiences{ get; set; }
}

如果需要转换，可以在dbcontext中转换。

   modelBuilder.Entity<Audience>().Property(b => b.AudienceType).HasConversion(
            v => v.ToString(), v => (AudienceType)Enum.Parse(typeof(AudienceType), v));

然后迁移并更新数据库。您将获得它们之间的一对多关系。

0
投票

从 EF Core 8.0 开始，这一切现在都是自动的！ 您无需执行任何操作，系统会自动处理。

如果您希望您的 

enum
成为 
string
，请按照此处的文档操作：

https://learn.microsoft.com/en-us/ef/core/modeling/value-conversions?tabs=data-annotations#collections-of-primitives

并使用此序列化器选项：

var jsonSerializerOptions = new JsonSerializerOptions
{
    Converters =
    {
        new JsonStringEnumConverter()
    }
};
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