Map enum to string set default enum value via HasDefaultValueSql

[wangpengxpy]

First，mapping enum to tinyint is fine，code show as below

    public class Blog
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public Color Color { get; set; }
        public List<Post> Posts { get; set; }
    }

    public enum Color : byte
    {
        Black = 1,
        Red,
        Blue
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
         modelBuilder.Entity<Blog>(b => 
         {
              b.Property(p => p.Color).HasDefaultValueSql("1");
         });
    }

but map to string can not work，code show as below

    public class Blog
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public Color Color { get; set; }
        public List<Post> Posts { get; set; }
    }

    public enum Color
    {
        Black = 1,
        Red,
        Blue
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
         modelBuilder.Entity<Blog>(b => 
         {
              b.Property(p => p.Color).HasColumnType("VARCHAR(20)").HasDefaultValueSql("Black");
        });
    }

The follow exception：

Microsoft.Data.SqlClient.SqlException: "The name" Black "is not allowed in this context. Valid expressions include constants, constant expressions, and variables (in some contexts). Column names are not allowed.

More details：

EF Core version: 3.1.1
Database provider: (Microsoft.EntityFrameworkCore.SqlServer)
Target framework: (.NET Core 3.1)
Operating system: Windows 10
IDE: (Visual Studio 2019 16.4.4)

[ajcvickers]

@wangpengxpy HasDefaultValueSql requires the raw SQL literal expression. Try .HasDefaultValueSql("'Black'"), or use .HasDefaultValue("Black") which will create the SQL literal from the given string.

[wangpengxpy]

@ajcvickers thanks your reply
use HasDefaultValueSql("'Black'") works，but try HasDefaultValue("Black") before and will throw an exception：System.InvalidOperationException:“Cannot set default value 'Black' of type 'System.String' on property 'Color' of type 'Model.Color' in entity type 'Blog'.” ,so I think using HasDefaultValue support is the best way in this case.Does it need improvement?

[ajcvickers]

@wangpengxpy Thanks for the additional info.

Team: I can reproduce the issue with HasDefaultValue("Black"). Stack trace:

"C:\Program Files\dotnet\dotnet.exe" C:/Stuff/MyRepros/AllTogetherNow/Local/bin/Debug/netcoreapp3.1/Local.dll
Unhandled exception. System.InvalidOperationException: Cannot set default value 'Black' of type 'System.String' on property 'Color' of type 'Color' in entity type 'Blog'.
   at Microsoft.EntityFrameworkCore.RelationalPropertyExtensions.ConvertDefaultValue(IProperty property, Object value)
   at Microsoft.EntityFrameworkCore.RelationalPropertyExtensions.SetDefaultValue(IMutableProperty property, Object value)
   at Microsoft.EntityFrameworkCore.RelationalPropertyBuilderExtensions.HasDefaultValue(PropertyBuilder propertyBuilder, Object value)
   at Microsoft.EntityFrameworkCore.RelationalPropertyBuilderExtensions.HasDefaultValue[TProperty](PropertyBuilder`1 propertyBuilder, Object value)
   at SomeDbContext.<>c.<OnModelCreating>b__0_0(EntityTypeBuilder`1 b) in C:\Stuff\MyRepros\AllTogetherNow\Local\Local.cs:line 49
   at Microsoft.EntityFrameworkCore.ModelBuilder.Entity[TEntity](Action`1 buildAction)
   at SomeDbContext.OnModelCreating(ModelBuilder modelBuilder) in C:\Stuff\MyRepros\AllTogetherNow\Local\Local.cs:line 47
   at Microsoft.EntityFrameworkCore.Infrastructure.ModelCustomizer.Customize(ModelBuilder modelBuilder, DbContext context)
   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.Infrastructure.DatabaseFacade.get_Dependencies()
   at Microsoft.EntityFrameworkCore.Infrastructure.DatabaseFacade.EnsureDeleted()
   at ThreeOne.Main() in C:\Stuff\MyRepros\AllTogetherNow\Local\Local.cs:line 22

[wangpengxpy]

@ajcvickers，thanks for reopening，I hope this problem can be improved

[ajcvickers]

@wangpengxpy The team pointed out to me that my suggestion to use .HasDefaultValue("Black") was incorrect. Because the property is an enum in the model, the enum value should be used here. For example, .HasDefaultValue(Color.Black). EF then does the conversion to string based on the mapping.

[johnwc]

@ajcvickers @tonysneed what about when you use scaffolding with a db first scenario, and use handlebars to set an entity's property to an enum? EF scaffolding automatically applies the .HasDefaultValue(0) to the property in OnModelCreating and throws the InvalidOperationException immediately.

[ErikEJ]

@johnwc That would be a Handlebars issue

[johnwc]

@ErikEJ How so? The error is occurring so early, I cannot overwrite the default value within the OnModelCreatingPartial method with the actual enum value. And there is no way for me to tell the scaffolding to not generate HasDefaultValue calls.

[ErikEJ]

@johnwc Maybe you should consider T4 templates?

[johnwc]

@ErikEJ do you have an example repo I can check out T4 templates with ef core scaffolding? What is the purpose of HasDefaultValue being called anyways for a db first scaffold entity? Why does EF need to know what the default value is, when the database is going to apply it anyways?

[ErikEJ]

I have some samples here: ErikEJ/EFCorePowerTools#1499