带有种子的添加迁移引发“未提供值”异常

Question

我正在尝试创建一个包，该包将帮助使用 JSON 文件中的数据为数据库播种，这些文件可以手动创建或从旧数据库中提取。目前，我创建了一个通用类SeedCreator<T>，它从给定文件（实体名称加上.json）中检索JSON，并将其反序列化为给定类型的对象。这部分工作正常。

为了使这个过程尽可能动态化，我通过使用命名空间Entities 识别所有类来对项目中的实体使用反射。有了这个，我遍历检索到的List 并检查 JSON 文件是否存在。如果是，我将路径和泛型类型传递给SeedsCreator 类。在运行Add-Migration 时进行调试时，数据会按照我对 JSON 文件的预期返回，但在变量modelBuilder 返回后，我收到错误The seed entity for entity type 'Table1' cannot be added because there was no value provided for the required property 'Id'.

如果我手动输入以下内容，它就可以正常工作。

modelBuilder.Entity(typeof(Table1)).HasData(data);

任何帮助将不胜感激。特别是如果我是盲人并且做了一些非常简单和愚蠢的事情。

public class Seeds
{
    public ModelBuilder CreateSeeds(ModelBuilder modelBuilder)
    {
        var entities = (from t in Assembly.GetExecutingAssembly().GetTypes()
                       where t.Namespace != null && (t.IsClass && t.Namespace.Contains("Entities"))
                       select t).ToList();

        foreach (var type in entities)
        {
            if (File.Exists("./Seeds/" + type.Name + ".json"))
            {
                Type[] typeArr = { type };
                var seeds = typeof(SeedCreator<>).MakeGenericType(typeArr);
                var activatedSeeds = Activator.CreateInstance(seeds);
                var data = seeds.GetMethod("GetSeeds")?.Invoke(activatedSeeds, new object[] { "./Seeds/" + type.Name + ".json" });
                modelBuilder.Entity(type).HasData(data);
            }
        }

        return modelBuilder;
    }
}

public class SeedCreator<T>
{
    public List<T> GetSeeds(string jsonPath)
    {
        using (var sr = new StreamReader(jsonPath))
            return JsonConvert.DeserializeObject<List<T>>(sr.ReadToEnd());
    }
}

public class Table1
{
    public int Id { get; set; }
}

在 DbContext 内部

using (var dataSeed = new Seeds()) modelBuilder = dataSeed.CreateSeeds(modelBuilder);

示例 JSON 文件 (Table1.json)

[
  {
    "id": 1
  },
  {
    "id": 2
  }
]

堆栈跟踪

System.InvalidOperationException: The seed entity for entity type 'Table1' cannot be added because there was no value provided for the required property 'Id'. at Microsoft.EntityFrameworkCore.Infrastructure.ModelValidator.ValidateData(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.Metadata.Conventions.Internal.ValidatingConvention.Apply(InternalModelBuilder modelBuilder) at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.ConventionDispatcher.ImmediateConventionScope.OnModelBuilt(InternalModelBuilder modelBuilder) at Microsoft.EntityFrameworkCore.ModelBuilder.FinalizeModel() at System.Lazy`1.ViaFactory(LazyThreadSafetyMode mode) at System.Lazy`1.ExecutionAndPublication(LazyHelper executionAndPublication, Boolean useDefaultConstructor) at System.Lazy`1.CreateValue() at Microsoft.EntityFrameworkCore.Internal.DbContextServices.CreateModel() at Microsoft.EntityFrameworkCore.Internal.DbContextServices.get_Model() at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped(ScopedCallSite scopedCallSite, ServiceProviderEngineScope scope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitConstructor(ConstructorCallSite constructorCallSite, ServiceProviderEngineScope scope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped(ScopedCallSite scopedCallSite, ServiceProviderEngineScope scope) 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.Internal.InternalAccessorExtensions.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.OperationBase.<>c__DisplayClass3_0`1.<Execute>b__0() at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)

Answer 1

你正陷入典型的params object[] 陷阱。

HasData 方法有 2 个重载 - 一个带有 params object[] data，另一个带有 IEnumerable<object> data。由于反射调用，您的data 变量的类型是object。因此，您使用 single 项 object[] 调用第一个重载，其中包含您的 data。

如果您想知道为什么异常消息告诉您没有为属性提供值，那么解释很简单。 HasData 不要求传递的对象与被播种的实体类型相同。这是为了允许指定实体类中不存在但数据播种所需的阴影属性。因此，它允许您传递包含所有实体属性的任何匿名或具体类型。

因此它试图反映传递对象的实际类型并找到属性Id。由于在您的情况下传递的单个对象的实际类型是List<TEntity>，当然它没有Id 属性，因此出现异常消息。

话虽如此，修复当然是调用正确的HasData 重载（使用IEnumerable<object> data）：

modelBuilder.Entity(type).HasData((IEnumerable<object>)data);