efcore: EFCore 2.1 - System.NullReferenceException: Object reference not set to an instance of an object. at Microsoft.EntityFrameworkCore.Extensions.Internal.EFPropertyExtensions.CreateEFPropertyExpression

I have just upgraded an existing project to EntityFrameworkCore 2.1

A query that was previously working is now throwing a null reference exception. I have put calls to .ToList() at various points through building up my query and it seems to be something to do with the call to automapper ProjectTo.

This doesn’t happen for all my queries though.

This is the exception I am getting:

System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.EntityFrameworkCore.Extensions.Internal.EFPropertyExtensions.CreateEFPropertyExpression(Expression target, Type propertyDeclaringType, Type propertyType, String propertyName, Boolean makeNullable)
   at Microsoft.EntityFrameworkCore.Extensions.Internal.EFPropertyExtensions.CreateEFPropertyExpression(Expression target, IPropertyBase property, Boolean makeNullable)
   at Microsoft.EntityFrameworkCore.Query.ExpressionVisitors.Internal.EntityEqualityRewritingExpressionVisitor.RewriteNullEquality(ExpressionType nodeType, Expression nonNullExpression)
   at Microsoft.EntityFrameworkCore.Query.ExpressionVisitors.Internal.EntityEqualityRewritingExpressionVisitor.VisitBinary(BinaryExpression binaryExpression)
   at System.Linq.Expressions.BinaryExpression.Accept(ExpressionVisitor visitor)
   at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
   at System.Linq.Expressions.ExpressionVisitor.VisitConditional(ConditionalExpression node)
   at System.Linq.Expressions.ConditionalExpression.Accept(ExpressionVisitor visitor)
   at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
   at System.Linq.Expressions.ExpressionVisitor.VisitMemberAssignment(MemberAssignment node)
   at System.Linq.Expressions.ExpressionVisitor.VisitMemberBinding(MemberBinding node)
   at System.Linq.Expressions.ExpressionVisitor.Visit[T](ReadOnlyCollection`1 nodes, Func`2 elementVisitor)
   at System.Linq.Expressions.ExpressionVisitor.VisitMemberInit(MemberInitExpression node)
   at System.Linq.Expressions.MemberInitExpression.Accept(ExpressionVisitor visitor)
   at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
   at Remotion.Linq.Clauses.SelectClause.TransformExpressions(Func`2 transformation)
   at Remotion.Linq.QueryModel.TransformExpressions(Func`2 transformation)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryOptimizer.Optimize(QueryCompilationContext queryCompilationContext, QueryModel queryModel)
   at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.OptimizeQueryModel(QueryModel queryModel, Boolean asyncQuery)
   at Microsoft.EntityFrameworkCore.Query.RelationalQueryModelVisitor.OptimizeQueryModel(QueryModel queryModel, Boolean asyncQuery)
   at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.CreateQueryExecutor[TResult](QueryModel queryModel)
   at Microsoft.EntityFrameworkCore.Storage.Database.CompileQuery[TResult](QueryModel queryModel)
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.CompileQueryCore[TResult](Expression query, IQueryModelGenerator queryModelGenerator, IDatabase database, IDiagnosticsLogger`1 logger, Type contextType)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass13_0`1.<Execute>b__0()
   at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQueryCore[TFunc](Object cacheKey, Func`1 compiler)
   at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQuery[TResult](Object cacheKey, Func`1 compiler)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.Execute[TResult](Expression query)
   at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.Execute[TResult](Expression expression)
   at Remotion.Linq.QueryableBase`1.GetEnumerator()
   at System.Collections.Generic.List`1.AddEnumerable(IEnumerable`1 enumerable)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at Momenta.People.HierarchicalConfiguration.HierarchicalConfigurationController`3.GetConfiguration(ODataQueryOptions`1 queryOptions, Request`1 query) in D:\code\Momenta.People\src\Momenta.People\HierarchicalConfiguration\HierarchicalConfigurationController.cs:line 191
   at lambda_method(Closure , Object )
   at Microsoft.Extensions.Internal.ObjectMethodExecutorAwaitable.Awaiter.GetResult()
   at Microsoft.AspNetCore.Mvc.Internal.ActionMethodExecutor.AwaitableObjectResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
   at System.Threading.Tasks.ValueTask`1.get_Result()
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.InvokeActionMethodAsync()
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.InvokeNextActionFilterAsync()
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.Rethrow(ActionExecutedContext context)
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.InvokeInnerFilterAsync()
   at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.InvokeNextResourceFilter()
   at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.Rethrow(ResourceExecutedContext context)
   at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.InvokeFilterPipelineAsync()
   at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.InvokeAsync()
   at Microsoft.AspNetCore.Builder.RouterMiddleware.Invoke(HttpContext httpContext)
   at Microsoft.AspNetCore.Localization.RequestLocalizationMiddleware.Invoke(HttpContext context)
   at NewOrbit.Mediatr.Authorisation.AspNetCore.AuthorisationFailureMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.StaticFiles.StaticFileMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.HttpProtocol.ProcessRequests[TContext](IHttpApplication`1 application)

Further technical details

EF Core version: 2.1 Database Provider: Microsoft.EntityFrameworkCore.SqlServer Operating system: Windows 10 IDE: Visual Studio 2017 15.7.4)

About this issue

Original URL
State: closed
Created 6 years ago
Comments: 16 (5 by maintainers)

Most upvoted comments

For the original exception message Duplicate of #12738

smitpatel on Aug 1, 2018

The issues appear to have the same underlying cause. I read this issue before submitting mine and failed to see the similarity because I didn’t inspect the sample you provided properly.

Specifically the issue is seen when accessing a collection of a child model within a .Select on a parent model. The issue occurs in this code because the .GroupBy causes a collection of ThingTypeModels to be created, which is then accessed with .First

Removing the Type obviously stops the above condition from being true. You will also find no failure without the .GroupBy, because accessing a singular navigational property is not flawed. e.g. Type.Name

Edit: To clarify: the issue is seen when accessing the child collection requires a JOIN . It appears that JOIN isn’t happening when using .Select to project to a different model.

MattOG on Jul 4, 2018

OK I have managed to reproduce this. Seems to be some combination of a GroupBy call and projecting to a model with a property named Type. Not sure why these specific situations cause this issue.

Can see repro here: https://github.com/hisuwh/EFAutomapperBugRepro

hisuwh on Jul 3, 2018

I’ve done some further investigation and it seems that all of the classes this are failing with have a property called Type. As soon I comment this out of the models I am projecting to it works.

hisuwh on Jul 3, 2018

Try again… This error exhibits behaviour similar to the issue I reported. Using a .ToList() to execute the query before projecting with the .Select() works. Projecting through two objects fails: .Collection().Object.Object.Property … I’m unsure as to why AutoMapper is causing an object graph deep enough to trigger this error from a single .GroupBy(), but maybe the code I have will help find the problem:

https://github.com/MattOG/WebErrorSample

MattOG on Jul 13, 2018

For further investigation, we need repro code which demonstrate the issue without using AutoMapper, OData libs and pure EF Core query.

smitpatel on Jul 6, 2018

Worth noting that I tried without the group by clause also and this works fine so it seems to be some combination of these things

hisuwh on Jul 3, 2018