我正在将代码优先 POCO 与 EF4、CTP5 结合使用。我有一张表，里面有很多列(超过 100 列)。我想将表拆分为多种类型(又名“表拆分”)，这样我就不必每次需要一些基本信息时都获取所有数据。

我似乎无法使用 Google 找到与此相关的任何文档。我找到了对概念“表拆分”的引用，并且我还看到了如何使用 EDMX 文件执行此操作，但没有代码优先的示例。

我希望它会像定义另一个实体类型一样简单，并将它们关联起来，就像您关联任何其他导航属性一样......

public class User
{
    public int UserID { get; set; }
    public string UserName { get; set; }
    [ForeignKey("UserID")]
    public virtual UserDetails Details { get; set; }
}

public class UserDetails
{
    public int UserID { get; set; }
    public string MoreData { get; set; }
    [ForeignKey("UserID")]
    public virtual User User { get; set; } // nice to have, but not required
}

我这样调用它......

return (from u in Context.Users  // <-- error occurs here
        where u.UserID == userID
        select u).FirstOrDefault();

不幸的是，这似乎不起作用。执行此操作时出现以下错误...

[IndexOutOfRangeException: Index was outside the bounds of the array.]
   System.Data.Entity.ModelConfiguration.Conventions.Edm.PropertyMaxLengthConvention.System.Data.Entity.ModelConfiguration.Conventions.Edm.IEdmConvention<System.Data.Edm.EdmAssociationType>.Apply(EdmAssociationType associationType, EdmModel model) +598
   System.Data.Entity.ModelConfiguration.Configuration.EdmConventionDispatcher.Dispatch(TEdmDataModelItem item) +100
   System.Data.Entity.ModelConfiguration.Configuration.EdmConventionDispatcher.VisitEdmAssociationType(EdmAssociationType item) +22
   System.Data.Entity.ModelConfiguration.Edm.Services.DataModelItemVisitor.VisitCollection(IEnumerable`1 collection, Action`1 visitMethod) +267
   System.Data.Entity.ModelConfiguration.Edm.Services.EdmModelVisitor.VisitAssociationTypes(EdmNamespace edmNamespace, IEnumerable`1 associationTypes) +75
   System.Data.Entity.ModelConfiguration.Edm.Services.EdmModelVisitor.VisitEdmNamespace(EdmNamespace item) +91
   System.Data.Entity.ModelConfiguration.Configuration.EdmConventionDispatcher.VisitEdmNamespace(EdmNamespace item) +32
   System.Data.Entity.ModelConfiguration.Edm.Services.DataModelItemVisitor.VisitCollection(IEnumerable`1 collection, Action`1 visitMethod) +267
   System.Data.Entity.ModelConfiguration.Edm.Services.EdmModelVisitor.VisitNamespaces(EdmModel model, IEnumerable`1 namespaces) +75
   System.Data.Entity.ModelConfiguration.Edm.Services.EdmModelVisitor.VisitEdmModel(EdmModel item) +47
   System.Data.Entity.ModelConfiguration.Configuration.EdmConventionDispatcher.VisitEdmModel(EdmModel item) +45
   System.Data.Entity.ModelConfiguration.Configuration.ConventionsConfiguration.ApplyModel(EdmModel model) +254
   System.Data.Entity.ModelConfiguration.ModelBuilder.Build(DbProviderManifest providerManifest, DbProviderInfo providerInfo, Boolean validateModel) +257
   System.Data.Entity.ModelConfiguration.ModelBuilder.Build(DbConnection providerConnection) +172
   System.Data.Entity.Internal.LazyInternalContext.CreateModel() +62
   System.Lazy`1.CreateValue() +361
   System.Lazy`1.LazyInitValue() +104
   System.Lazy`1.get_Value() +89
   System.Data.Entity.Internal.LazyInternalContext.InitializeContext() +358
   System.Data.Entity.Internal.InternalContext.Initialize() +16
   System.Data.Entity.Internal.InternalContext.GetEntitySetAndBaseTypeForType(Type entityType) +16
   System.Data.Entity.Internal.Linq.InternalSet`1.Initialize() +61
   System.Data.Entity.Internal.Linq.InternalSet`1.get_Provider() +15
   System.Data.Entity.Infrastructure.DbQuery`1.System.Linq.IQueryable.get_Provider() +13
   System.Linq.Queryable.Where(IQueryable`1 source, Expression`1 predicate) +63
   TourFactory.Web.AgentWebsite.Models.Websites.WebsiteRepository.GetUser(Int32 userID) in C:\Code\hdtf\TF4\Web\AgentWebsite\Models\Websites\WebsiteRepository.cs:28
   TourFactory.Web.AgentWebsite.Controllers.WebsiteController.get_Agent() in C:\Code\hdtf\TF4\Web\AgentWebsite\Controllers\WebsiteController.cs:42
   TourFactory.Web.AgentWebsite.Controllers.WebsiteController.OnActionExecuting(ActionExecutingContext filterContext) in C:\Code\hdtf\TF4\Web\AgentWebsite\Controllers\WebsiteController.cs:55
   System.Web.Mvc.Controller.System.Web.Mvc.IActionFilter.OnActionExecuting(ActionExecutingContext filterContext) +39
   System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func`1 continuation) +81
   System.Web.Mvc.<>c__DisplayClass17.<InvokeActionMethodWithFilters>b__14() +61
   System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodWithFilters(ControllerContext controllerContext, IList`1 filters, ActionDescriptor actionDescriptor, IDictionary`2 parameters) +305
   System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName) +830
   System.Web.Mvc.Controller.ExecuteCore() +136
   System.Web.Mvc.ControllerBase.Execute(RequestContext requestContext) +232
   System.Web.Mvc.ControllerBase.System.Web.Mvc.IController.Execute(RequestContext requestContext) +39
   System.Web.Mvc.<>c__DisplayClassb.<BeginProcessRequest>b__5() +68
   System.Web.Mvc.Async.<>c__DisplayClass1.<MakeVoidDelegate>b__0() +44
   System.Web.Mvc.Async.<>c__DisplayClass8`1.<BeginSynchronous>b__7(IAsyncResult _) +42
   System.Web.Mvc.Async.WrappedAsyncResult`1.End() +141
   System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, Object tag) +54
   System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, Object tag) +40
   System.Web.Mvc.<>c__DisplayClasse.<EndProcessRequest>b__d() +61
   System.Web.Mvc.SecurityUtil.<GetCallInAppTrustThunk>b__0(Action f) +31
   System.Web.Mvc.SecurityUtil.ProcessInApplicationTrust(Action action) +56
   System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +110
   System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result) +38
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +8841105
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +184

删除 User.Details 属性会使错误消失，但我无法使用 EF4 的漂亮导航功能。

最佳答案

使用复杂类型 是将一个表映射到多个类型的唯一方法。但是，Code First(和一般的 EF)不支持复杂类型的延迟/延迟加载。换句话说，每次您从数据库中读取实体时，EF 总是会填充复杂类型:

public class User
{
    public int UserID { get; set; }
    public string UserName { get; set; }
    public UserDetails Details { get; set; }
}

[ComplexType]
public class UserDetails
{
    public string MoreData { get; set; }
}

为您的大表实现延迟加载的唯一方法是将其真正拆分为多个表，然后您可以使用一对一关联将其映射回多个实体。

有关 EF Code First CTP 中复杂类型的更多信息，请查看这篇文章:
Associations in EF Code First CTP5: Part 1 – Complex Types

https://stackoverflow.com/questions/4739717/