如何在 Entity Framework Core 中创建没有主键的 table？

Question

我有一个旧数据库，其中有一些 table 没有主键。现在我将我的旧项目移动到 Asp.Net Core 并使用 Entity Framework Core 2.0.1 Code First 方法。我制作了 table 的模型 class 并尝试使用 Add-Migration 添加迁移，但它给出了以下错误。我认为从技术上讲它的预期行为，但是还有哪些其他替代方法可以让我不需要修改现有的 table 架构。

System.InvalidOperationException: The entity type 'TestTable' requires a primary key to be defined. at Microsoft.EntityFrameworkCore.Infrastructure.ModelValidator.ValidateNonNullPrimaryKeys(IModel model) at Microsoft.EntityFrameworkCore.Infrastructure.ModelValidator.Validate(IModel model) at Microsoft.EntityFrameworkCore.Infrastructure.RelationalModelValidator.Validate(IModel model) at Microsoft.EntityFrameworkCore.Internal.SqlServerModelValidator.Validate(IModel model) at Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.CreateModel(DbContext context, IConventionSetBuilder conventionSetBuilder, IModelValidator validator) at System.Collections.Concurrent.ConcurrentDictionary2.GetOrAdd(TKey key, Func2 valueFactory) at Microsoft.EntityFrameworkCore.Internal.DbContextServices.CreateModel() at Microsoft.EntityFrameworkCore.Internal.DbContextServices.get_Model()
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactory(FactoryCallSite factoryCallSite, ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor2.VisitCallSite(IServiceCallSite callSite, TArgument argument) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped(ScopedCallSite scopedCallSite, ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor2.VisitCallSite(IServiceCallSite callSite, TArgument argument) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitConstructor(ConstructorCallSite constructorCallSite, ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor2.VisitCallSite(IServiceCallSite callSite, TArgument argument) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped(ScopedCallSite scopedCallSite, ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor2.VisitCallSite(IServiceCallSite callSite, TArgument argument) at Microsoft.Extensions.DependencyInjection.ServiceProvider.<>c__DisplayClass22_0.b__0(ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceProvider.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.Infrastructure.AccessorExtensions.GetService[TService](IInfrastructure1 accessor) at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext(Func1 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.OperationBase.<>c__DisplayClass3_0`1.b__0() at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action) The entity type 'TestTable' requires a primary key to be defined.

型号class:

public class TestTable
{
    [StringLength(255)]
    public string Col1 { get; set; }
    [Required]
    public int Col2 { get; set; }
    [Required]
    public int Col3 { get; set; }
    public DateTime? Col4 { get; set; }
    [Required]
    public int Col5 { get; set; }
    [Required]
    public int Col6 { get; set; }
    [Required]
    public int Col7 { get; set; }
}

我想到了一种解决方案，比如添加一个自动增量标识列作为 PK。请建议一个好的和正确的方法来做到这一点？

[Key]
public int Id { get; set; }

Answer 1

上下文的代码文件中：

protected override void OnModelCreating( DbModelBuilder model_builder )
{
    base.OnModelCreating( model_builder );
    model_builder.Entity<TestTable>().HasKey(
        t => new { t.Id }
    );
}

所以基本上你只需要指定哪些列可以是主键。