Question

我有一个奇怪的问题，基本上我有这个代码：

var langauges = (from l in context.languages 
                 where Model.LanguageIDs.Contains(l.LanguageID) 
                 select l)
                .ToList<language>();

我不知道为什么，但我总是收到错误：

System.NullReferenceException：未将对象引用设置为对象的实例

事情是它以前工作，但之后我将我的所有应用程序升级到MVC5和EF6，它开始崩溃这个代码。

虽然如果我检查Model.Langauges，它有几个ID，所以没关系。

我也完成了背景。语言和所有人都有id。

我也是这样写的：

var langauges = (from l in context.languages 
                 where 1==l.LanguageID 
                 select l)
                .ToList<language>();

这也有效，所以我真的不明白，我做错了什么？

任何人都可以详细说明......？

堆栈跟踪：

   at MySql.Data.Entity.SqlGenerator.Visit(DbPropertyExpression expression)
   at MySql.Data.Entity.SqlGenerator.Visit(DbInExpression expression)
   at System.Data.Entity.Core.Common.CommandTrees.DbInExpression.Accept[TResultType](DbExpressionVisitor`1 visitor)
   at MySql.Data.Entity.SqlGenerator.VisitBinaryExpression(DbExpression left, DbExpression right, String op)
   at MySql.Data.Entity.SqlGenerator.Visit(DbAndExpression expression)
   at System.Data.Entity.Core.Common.CommandTrees.DbAndExpression.Accept[TResultType](DbExpressionVisitor`1 visitor)
   at MySql.Data.Entity.SelectGenerator.Visit(DbFilterExpression expression)
   at System.Data.Entity.Core.Common.CommandTrees.DbFilterExpression.Accept[TResultType](DbExpressionVisitor`1 visitor)
   at MySql.Data.Entity.SqlGenerator.VisitInputExpression(DbExpression e, String name, TypeUsage type)
   at MySql.Data.Entity.SelectGenerator.VisitInputExpressionEnsureSelect(DbExpression e, String name, TypeUsage type)
   at MySql.Data.Entity.SelectGenerator.Visit(DbProjectExpression expression)
   at System.Data.Entity.Core.Common.CommandTrees.DbProjectExpression.Accept[TResultType](DbExpressionVisitor`1 visitor)
   at MySql.Data.Entity.SelectGenerator.GenerateSQL(DbCommandTree tree)
   at MySql.Data.MySqlClient.MySqlProviderServices.CreateDbCommandDefinition(DbProviderManifest providerManifest, DbCommandTree commandTree)
   at System.Data.Entity.Core.Common.DbProviderServices.CreateDbCommandDefinition(DbProviderManifest providerManifest, DbCommandTree commandTree, DbInterceptionContext interceptionContext)
   at System.Data.Entity.Core.Common.DbProviderServices.CreateCommandDefinition(DbCommandTree commandTree, DbInterceptionContext interceptionContext)
   at System.Data.Entity.Core.EntityClient.Internal.EntityCommandDefinition..ctor(DbProviderFactory storeProviderFactory, DbCommandTree commandTree, DbInterceptionContext interceptionContext, IDbDependencyResolver resolver, BridgeDataReaderFactory bridgeDataReaderFactory, ColumnMapFactory columnMapFactory)
   at System.Data.Entity.Core.EntityClient.Internal.EntityProviderServices.CreateCommandDefinition(DbProviderFactory storeProviderFactory, DbCommandTree commandTree, DbInterceptionContext interceptionContext, IDbDependencyResolver resolver)
   at System.Data.Entity.Core.EntityClient.Internal.EntityProviderServices.CreateDbCommandDefinition(DbProviderManifest providerManifest, DbCommandTree commandTree, DbInterceptionContext interceptionContext)
   at System.Data.Entity.Core.Common.DbProviderServices.CreateCommandDefinition(DbCommandTree commandTree, DbInterceptionContext interceptionContext)
   at System.Data.Entity.Core.Objects.Internal.ObjectQueryExecutionPlanFactory.CreateCommandDefinition(ObjectContext context, DbQueryCommandTree tree)
   at System.Data.Entity.Core.Objects.Internal.ObjectQueryExecutionPlanFactory.Prepare(ObjectContext context, DbQueryCommandTree tree, Type elementType, MergeOption mergeOption, Boolean streaming, Span span, IEnumerable`1 compiledQueryParameters, AliasGenerator aliasGenerator)
   at System.Data.Entity.Core.Objects.ELinq.ELinqQueryState.GetExecutionPlan(Nullable`1 forMergeOption)
   at System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClassb.<GetResults>b__a()
   at System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction[T](Func`1 func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess)
   at System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClassb.<GetResults>b__9()
   at System.Data.Entity.Infrastructure.DefaultExecutionStrategy.Execute[TResult](Func`1 operation)
   at System.Data.Entity.Core.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption)
   at System.Data.Entity.Core.Objects.ObjectQuery`1.<System.Collections.Generic.IEnumerable<T>.GetEnumerator>b__0()
   at System.Lazy`1.CreateValue()
   at System.Lazy`1.LazyInitValue()
   at System.Lazy`1.get_Value()
   at System.Data.Entity.Internal.LazyEnumerator`1.MoveNext()
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at MyProject.Infrastructure.DAL.Operations.UpdateUserinfo(Int32 id, Model Model) in :line 168

Answer 1

Model.LanguageIDs可能null还是您的context尚未设置？

另外，您是否允许null中的language context.languages条目？如果其中任何一个是null，您将获得此例外。

Answer 2

好的，我遇到了完全相同的问题，但找到了可能对您有帮助的解决方案。

在我的案例中，LanguageIDs集合类型为List<long>（在DB中为unisgned int），LanguageID为int。而这种类型的差异造成了问题。

我知道，它仍然是一个bug，从.net的角度来看它绝对是正确的，但希望我的帖子会帮助某人

Int []。包含在EF6中不起作用

2 个答案: