EF Core中的枚举列表

Question

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; }
}

但当我运行add-migration AudienceType时，我会得到以下错误：

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：我看到了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呢？

Answer 1

要将枚举值列表表示为逗号分隔的字符串，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()
);
}

Answer 2

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);
}

它使用以下两个类别：

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())
{
}
}

Answer 3

因为enum不是一个类，所以需要编写一个新的类来封装它。

您可以创建一个新类：

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

然后在您的Restaurant:中

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中进行转换。

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。他们之间会有一对多的关系。