EF-Code First：无法创建类型''的常量值。 在此上下文中仅支持原始类型（例如Int32，String和Guid'）

Question

我目前在使用EF代码时遇到一些linq有问题。 我当前的代码工作正常：

我的数据库模型

public class MyDatabase : DbContext
{
     public DbSet<Person> People { get; set; }
     public DbSet<Role> Roles { get; set; }
     public DbSet<Visit> Visits { get; set; }
}

public class Person
{
     public int PersonId { get; set; }
     public string Forename { get; set; }
     public string Surname { get; set; }   
}

public class Visit
{
     public int VisitId { get; set; }
     public string Name {get; set;}
     public int PersonId { get; set; }
     public string VisitStatus { get; set; }
     public virtual Person People { get; set; }  
     //There is a one to many relationship to person
}

public class Role
{
    public Role()
    {
       People = new HashSet<Person>();
    }

    [Key]
    public int RoleId { get; set; }
    public string Name { get; set; }

    public virtual ICollection<Person> People { get; set; }
     //There is a many to many relationship to person
}

我的查询

public IEnumerable<VisitDetails> GetGuestVisiterList()
{
    using (var db = new MyDatabase())
    {
        return (from p in db.People
        where p.Roles.Any(a => a.Name == "Guest")
        select new GuestVisitDetails
            {
                PersonId = p.PersonId,
                Forename = p.Forename,
                Surname = p.Surname,
                NumberOfVisits = db.Visits.Count(v => v.PersonId == p.PersonId && v.VisitStatus != "Complete")
            }).ToList();

    }    
}

我的视图模型

public class GuestVisitDetails
{
    public int PersonId { get; set; }
    public string Forename { get; set; }
    public string Surname { get; set; }
    public int NumberOfVisits { get; set; }
}

但是当我尝试为我的数据库模型使用接口以便我可以进行单元测试时，会出现以下错误：

Unable to create a constant value of type 'MyVisits.Data.Model.Visit'. Only primitive types ('such as Int32, String, and Guid') are supported in this context

我的Datebase界面

public class MyDatabase : DbContext, IDolphinDatabase
{
     public IDbSet<Person> People { get; set; }
     public IDbSet<Role> Roles { get; set; }
     public IDbSet<Visit> Visits { get; set; }
}

public interface IMyDatabase : IDisposable
{
     public IDbSet<Person> People { get; set; }
     public IDbSet<Role> Roles { get; set; }
     public IDbSet<Visit> Visits { get; set; }
}

我的新查询，我创建了一个dbFactory来获取IMyDatabase

public IEnumerable<VisitDetails> GetGuestVisiterList(int paperId)
{
    using (var db = _dbFactory.GetDatabase())
    {
        return (from p in db.People
                where p.Roles.Any(a => a.Name == "Guest")
                select new GuestVisitDetails
                 {
                     PersonId = p.PersonId,
                     Forename = p.Forename,
                     Surname = p.Surname,
                     NumberOfVisits = db.Visits.Count(v => v.PersonId == p.PersonId && v.VisitStatus != "Complete")
                 }).ToList();
    }    
}

我发现导致问题的是'NumberOfVisits'，但我不确定为什么或如何修复它。

按要求堆栈跟踪

[NotSupportedException: Unable to create a constant value of type 'MyVisits.Data.Model.Visit'. Only primitive types ('such as Int32, String, and Guid') are supported in this context.]
System.Data.Objects.ELinq.ConstantTranslator.TypedTranslate(ExpressionConverter parent, ConstantExpression linq) +902
System.Data.Objects.ELinq.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq) +54
System.Data.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq) +110
System.Data.Objects.ELinq.<>c__DisplayClass77.<TypedTranslate>b__75(Expression e) +11
System.Linq.WhereSelectEnumerableIterator`2.MoveNext() +151
System.Data.Common.CommandTrees.ExpressionBuilder.Internal.EnumerableValidator`3.Validate(IEnumerable`1 argument, String argumentName, Int32 expectedElementCount, Boolean allowEmpty, Func`3 map, Func`2 collect, Func`3 deriveName) +237
System.Data.Common.CommandTrees.ExpressionBuilder.Internal.EnumerableValidator`3.Validate() +46
System.Data.Common.CommandTrees.ExpressionBuilder.Internal.ArgumentValidation.CreateExpressionList(IEnumerable`1 arguments, String argumentName, Boolean allowEmpty, Action`2 validationCallback) +142
System.Data.Common.CommandTrees.ExpressionBuilder.Internal.ArgumentValidation.ValidateNewCollection(IEnumerable`1 elements, DbExpressionList& validElements) +72
System.Data.Objects.ELinq.NewArrayInitTranslator.TypedTranslate(ExpressionConverter parent, NewArrayExpression linq) +121
System.Data.Objects.ELinq.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq) +54
System.Data.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq) +110
System.Data.Objects.ELinq.ConstantTranslator.TypedTranslate(ExpressionConverter parent, ConstantExpression linq) +520
System.Data.Objects.ELinq.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq) +54
System.Data.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq) +110
System.Data.Objects.ELinq.AggregateTranslator.Translate(ExpressionConverter parent, MethodCallExpression call) +86
System.Data.Objects.ELinq.SequenceMethodTranslator.Translate(ExpressionConverter parent, MethodCallExpression call, SequenceMethod sequenceMethod) +14
System.Data.Objects.ELinq.MethodCallTranslator.TypedTranslate(ExpressionConverter parent, MethodCallExpression linq) +102
System.Data.Objects.ELinq.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq) +54
System.Data.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq) +110
System.Data.Objects.ELinq.MemberInitTranslator.TypedTranslate(ExpressionConverter parent, MemberInitExpression linq) +310
System.Data.Objects.ELinq.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq) +54
System.Data.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq) +110
System.Data.Objects.ELinq.ExpressionConverter.TranslateLambda(LambdaExpression lambda, DbExpression input) +80
System.Data.Objects.ELinq.ExpressionConverter.TranslateLambda(LambdaExpression lambda, DbExpression input, DbExpressionBinding& binding) +88
System.Data.Objects.ELinq.OneLambdaTranslator.Translate(ExpressionConverter parent, MethodCallExpression call, DbExpression& source, DbExpressionBinding& sourceBinding, DbExpression& lambda) +85
System.Data.Objects.ELinq.SelectTranslator.Translate(ExpressionConverter parent, MethodCallExpression call) +37
System.Data.Objects.ELinq.SequenceMethodTranslator.Translate(ExpressionConverter parent, MethodCallExpression call, SequenceMethod sequenceMethod) +14
System.Data.Objects.ELinq.MethodCallTranslator.TypedTranslate(ExpressionConverter parent, MethodCallExpression linq) +102
System.Data.Objects.ELinq.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq) +54
System.Data.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq) +110
System.Data.Objects.ELinq.ExpressionConverter.Convert() +16
System.Data.Objects.ELinq.ELinqQueryState.GetExecutionPlan(Nullable`1 forMergeOption) +110
System.Data.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption) +149
System.Data.Objects.ObjectQuery`1.System.Collections.Generic.IEnumerable<T>.GetEnumerator() +44
System.Data.Entity.Internal.Linq.InternalQuery`1.GetEnumerator() +40
System.Data.Entity.Infrastructure.DbQuery`1.System.Collections.Generic.IEnumerable<TResult>.GetEnumerator() +40
System.Collections.Generic.List`1..ctor(IEnumerable`1 collection) +315
System.Linq.Enumerable.ToList(IEnumerable`1 source) +58
MyVisits.Business.<GetGuestVisiterList>c__Binding.Invoke(Object& instance, Arguments arguments, Object aspectArgs) in E:\Visual Studio\Projects\MyVisits_current\MyVisits.Business\VisitService.cs:459
PostSharp.Aspects.Internals.MethodInterceptionArgsImpl`1.Proceed() +23
MvcMiniProfiler.Aop.MiniProfilerAttribute.OnInvoke(MethodInterceptionArgs args) in E:\Visual Studio\Projects\MyVisits_current\MvcMiniProfiler.Aop\MiniProfilerAttribute.cs:17
MyVisits.Business.VisitService.GetGuestVisiterList() in :0
MyVisits.Web.Areas.RegionalAdministrator.Controllers.VisitController.EditVisitor() in E:\Visual Studio\Projects\MyVisits_current\MyVisits.Web\Areas\RegionalAdministrator\Controllers\VisitController.cs:85
lambda_method(Closure , ControllerBase , Object[] ) +101
System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object[] parameters) +17
System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary`2 parameters) +208
Castle.Proxies.ControllerActionInvokerProxy.InvokeActionMethod_callback(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters) +27
Castle.Proxies.Invocations.ControllerActionInvoker_InvokeActionMethod.InvokeMethodOnTarget() +154
Castle.DynamicProxy.AbstractInvocation.Proceed() +56
Glimpse.Mvc3.Interceptor.InvokeActionMethodInterceptor.Intercept(IInvocation invocation) +336
Castle.DynamicProxy.AbstractInvocation.Proceed() +94
Castle.Proxies.ControllerActionInvokerProxy.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters) +214
System.Web.Mvc.<>c__DisplayClass15.<InvokeActionMethodWithFilters>b__12() +55
System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func`1 continuation) +263
System.Web.Mvc.<>c__DisplayClass17.<InvokeActionMethodWithFilters>b__14() +19
System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func`1 continuation) +263
System.Web.Mvc.<>c__DisplayClass17.<InvokeActionMethodWithFilters>b__14() +19
System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodWithFilters(ControllerContext controllerContext, IList`1 filters, ActionDescriptor actionDescriptor, IDictionary`2 parameters) +191
System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName) +343
System.Web.Mvc.Controller.ExecuteCore() +116
System.Web.Mvc.ControllerBase.Execute(RequestContext requestContext) +97
System.Web.Mvc.ControllerBase.System.Web.Mvc.IController.Execute(RequestContext requestContext) +10
System.Web.Mvc.<>c__DisplayClassb.<BeginProcessRequest>b__5() +37
System.Web.Mvc.Async.<>c__DisplayClass1.<MakeVoidDelegate>b__0() +21
System.Web.Mvc.Async.<>c__DisplayClass8`1.<BeginSynchronous>b__7(IAsyncResult _) +12
System.Web.Mvc.Async.WrappedAsyncResult`1.End() +62
System.Web.Mvc.<>c__DisplayClasse.<EndProcessRequest>b__d() +50
System.Web.Mvc.SecurityUtil.<GetCallInAppTrustThunk>b__0(Action f) +7
System.Web.Mvc.SecurityUtil.ProcessInApplicationTrust(Action action) +22
System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +60
System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result) +9
System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +8920029
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +184

任何帮助都会很棒

Answer 1

首先，您应该更改您的实体，以支持您的关系：

public class Person
{
     public int PersonId { get; set; }
     public string Forename { get; set; }
     public string Surname { get; set; } 

     // add a collection-reference to roles
     public virtual ICollection<Role> Roles { get; set; } 

     // add a collection-reference to visites
     public virtual ICollection<Visit> Visits { get; set; }  
}

---

public class Visit
{
     public int VisitId { get; set; }
     public string Name {get; set;}
     public string VisitStatus { get; set; }

     public int PersonId { get; set; }
     public virtual Person People { get; set; }  
     //There is a one to many relationship to person
}

---

public class Role
{
    public Role()
    {
       People = new HashSet<Person>();
    }

    [Key]
    public int RoleId { get; set; }
    public string Name { get; set; }

    public virtual ICollection<Person> People { get; set; }
     //There is a many to many relationship to person
}

你的问题现在解决了。 但您也可以像这样更改查询：

public IEnumerable<VisitDetails> GetGuestVisiterList(int paperId)
{
    using (var db = _dbFactory.GetDatabase())
    {
        return (from p in db.People
                where p.Roles.Any(a => a.Name == "Guest")
                select new GuestVisitDetails
                 {
                     PersonId = p.PersonId,
                     Forename = p.Forename,
                     Surname = p.Surname,
                     NumberOfVisits = p.Visits.Count(v => v.VisitStatus != "Complete")
                 }).ToList();
    }    
}

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