System.Linq.Expressions - 由于对象的当前状态，操作无效

Question

在我的 ASP.NET Core MVC 应用程序中，我在跟踪引用其他 LINQ 查询的 LINQ 查询时遇到上述错误。为了这篇文章的简单起见，为了简洁起见，我在这里修改了代码，因为实际查询太长且太复杂。 问题：错误的可能原因是什么？我应该在哪里进一步调试问题？如果有帮助，错误详细信息如下所示。

视图模型：

public class MyViewModel
{
    public string Prop1 { get; set; }
    public int Prop2 { get; set; }
}

控制器：

public ActionResult Index()
{
    var vm = (from q5 in LINQ_Qry5
             join q4 in LINQ_Qry4 on q5.SomeID equals q4.SomeID
             select new MyViewModel { Prop1= q5.property1, Prop2 = q4.property2}).ToList();
            return View(vm);
}

错误详情：

  Message=Operation is not valid due to the current state of the object.
  Source=System.Linq.Expressions
  StackTrace:
       at System.Linq.Expressions.MethodCallExpression2.GetArgument(Int32 index)
       at System.Dynamic.Utils.ListArgumentProvider.get_Item(Int32 index)
       at Microsoft.EntityFrameworkCore.Query.ExpressionVisitors.Internal.QueryFlattener.Flatten(MethodCallExpression methodCallExpression)
       at Microsoft.EntityFrameworkCore.Query.RelationalQueryModelVisitor.OptimizeJoinClause(JoinClause joinClause, QueryModel queryModel, Int32 index, Action baseVisitAction, MethodInfo operatorToFlatten, Boolean outerJoin)
       at Microsoft.EntityFrameworkCore.Query.RelationalQueryModelVisitor.VisitJoinClause(JoinClause joinClause, QueryModel queryModel, Int32 index)
       at Remotion.Linq.QueryModelVisitorBase.VisitBodyClauses(ObservableCollection`1 bodyClauses, QueryModel queryModel)
       at Remotion.Linq.QueryModelVisitorBase.VisitQueryModel(QueryModel queryModel)
       at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.VisitQueryModel(QueryModel queryModel)
       at Microsoft.EntityFrameworkCore.Query.RelationalQueryModelVisitor.VisitQueryModel(QueryModel queryModel)
       at Microsoft.EntityFrameworkCore.Query.Internal.SqlServerQueryModelVisitor.VisitQueryModel(QueryModel queryModel)
       at Microsoft.EntityFrameworkCore.Query.ExpressionVisitors.RelationalEntityQueryableExpressionVisitor.VisitSubQuery(SubQueryExpression expression)
       at Microsoft.EntityFrameworkCore.Query.ExpressionVisitors.ExpressionVisitorBase.Visit(Expression node)
       at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.ReplaceClauseReferences(Expression expression, IQuerySource querySource, Boolean inProjection)
       at Microsoft.EntityFrameworkCore.Query.RelationalQueryModelVisitor.CompileMainFromClauseExpression(MainFromClause mainFromClause, QueryModel queryModel)
       at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.VisitMainFromClause(MainFromClause fromClause, QueryModel queryModel)
       at Remotion.Linq.QueryModelVisitorBase.VisitQueryModel(QueryModel queryModel)
       at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.VisitQueryModel(QueryModel queryModel)
       at Microsoft.EntityFrameworkCore.Query.RelationalQueryModelVisitor.VisitQueryModel(QueryModel queryModel)
       at Microsoft.EntityFrameworkCore.Query.Internal.SqlServerQueryModelVisitor.VisitQueryModel(QueryModel queryModel)
       at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.CreateQueryExecutor[TResult](QueryModel queryModel)
    --- End of stack trace from previous location where exception was thrown ---
       at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()

Answer 1

我打算把它作为评论，但它说的字符太多。

无论如何，从我对这个错误的谷歌搜索来看，问题似乎在于您的任何一个（或一些）变量为 null 或 empty。

确保以下几点：

1. 您的 join 不返回 null 或空序列
2. 你的q5和q4中的property1和property2存在且不为空
3. 也许还可以确保当 vm 为空或 null 时View(vm) 不是问题。

---

我查看的一些链接：

UpdateException: Operation is not valid due to...

MonoTouch & LINQ - Operation is not valid due to the current state of the object

Answer 2

var vm = (from q5 in LINQ_Qry5
             join q4 in LINQ_Qry4 on q5.SomeID equals q4.SomeID
             select new MyViewModel() { Prop1= q5.property1, prop2 = q4.property2}).ToList();
            return View(vm);