LINQ to Entities无法识别方法’System.String StringConvert（System.Nullable`1 ）

我无法弄清楚为什么我会收到这个错误。 我已经使用此function与以前版本的Entity Framework成功使用，但我使用EF6设置了一个新项目并且它没有合作。

using System.Data; using System.Data.Objects.SqlClient; e.Result = from n in MyDB.tblBulletins where n.AnncStart  DateTime.Now && n.Approved == true orderby n.AnncStart descending, n.AnncDate descending select new { n.RecID, AnncTitle = n.AnncTitle + " ", AnncText = (n.AnncImg == null ? n.AnncText : "" + n.AnncText), Email = (n.Email == null ? "" : "
" + n.Email + ""), n.AnncType, n.AnncDate, n.AnncEnd, n.v_EmpBasicInfo.Name }; 

当我运行这个时，我得到LINQ to Entities无法识别方法’System.String StringConvert（System.Nullable`1 [System.Double]）’方法，并且此方法无法转换为商店表达式。

n.RecID是SQL数据库（SQL Server标准版）中表的int主键

我似乎通过搜索找到的是人们推荐StringConvert而不是ToString

附加 – 堆栈跟踪：

 [NotSupportedException: LINQ to Entities does not recognize the method 'System.String StringConvert(System.Nullable`1[System.Double])' method, and this method cannot be translated into a store expression.] System.Data.Entity.Core.Objects.ELinq.DefaultTranslator.Translate(ExpressionConverter parent, MethodCallExpression call) +194 System.Data.Entity.Core.Objects.ELinq.MethodCallTranslator.TypedTranslate(ExpressionConverter parent, MethodCallExpression linq) +976 System.Data.Entity.Core.Objects.ELinq.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq) +88 System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq) +148 System.Data.Entity.Core.Objects.ELinq.BinaryTranslator.TypedTranslate(ExpressionConverter parent, BinaryExpression linq) +122 System.Data.Entity.Core.Objects.ELinq.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq) +88 System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq) +148 System.Data.Entity.Core.Objects.ELinq.BinaryTranslator.TypedTranslate(ExpressionConverter parent, BinaryExpression linq) +87 System.Data.Entity.Core.Objects.ELinq.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq) +88 System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq) +148 System.Data.Entity.Core.Objects.ELinq.NewTranslator.TypedTranslate(ExpressionConverter parent, NewExpression linq) +520 System.Data.Entity.Core.Objects.ELinq.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq) +88 System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq) +148 System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateLambda(LambdaExpression lambda, DbExpression input) +168 System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateLambda(LambdaExpression lambda, DbExpression input, DbExpressionBinding& binding) +160 System.Data.Entity.Core.Objects.ELinq.OneLambdaTranslator.Translate(ExpressionConverter parent, MethodCallExpression call, DbExpression& source, DbExpressionBinding& sourceBinding, DbExpression& lambda) +168 System.Data.Entity.Core.Objects.ELinq.SelectTranslator.Translate(ExpressionConverter parent, MethodCallExpression call) +70 System.Data.Entity.Core.Objects.ELinq.SequenceMethodTranslator.Translate(ExpressionConverter parent, MethodCallExpression call, SequenceMethod sequenceMethod) +47 System.Data.Entity.Core.Objects.ELinq.MethodCallTranslator.TypedTranslate(ExpressionConverter parent, MethodCallExpression linq) +141 System.Data.Entity.Core.Objects.ELinq.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq) +88 System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq) +148 System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.Convert() +50 System.Data.Entity.Core.Objects.ELinq.ELinqQueryState.GetExecutionPlan(Nullable`1 forMergeOption) +563 System.Data.Entity.Core.Objects.c__DisplayClassb.b__a() +83 System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction(Func`1 func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess) +499 System.Data.Entity.Core.Objects.c__DisplayClassb.b__9() +271 System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute(Func`1 operation) +251 System.Data.Entity.Core.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption) +600 System.Data.Entity.Core.Objects.ObjectQuery`1.<System.Collections.Generic.IEnumerable.GetEnumerator>b__0() +89 System.Lazy`1.CreateValue() +416 System.Lazy`1.LazyInitValue() +152 System.Lazy`1.get_Value() +75 System.Data.Entity.Internal.LazyEnumerator`1.MoveNext() +40 System.Collections.Generic.List`1..ctor(IEnumerable`1 collection) +381 System.Linq.Enumerable.ToList(IEnumerable`1 source) +58 [TargetInvocationException: Exception has been thrown by the target of an invocation.] System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor) +0 System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments) +92 System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture) +108 System.Reflection.MethodBase.Invoke(Object obj, Object[] parameters) +19 System.Web.UI.WebControls.QueryableDataSourceHelper.ToList(IQueryable query, Type dataObjectType) +225 System.Web.UI.WebControls.LinqDataSourceView.ExecuteSelect(DataSourceSelectArguments arguments) +549 System.Web.UI.WebControls.Repeater.GetData() +55 System.Web.UI.WebControls.Repeater.CreateControlHierarchy(Boolean useDataSource) +89 System.Web.UI.WebControls.Repeater.OnDataBinding(EventArgs e) +61 System.Web.UI.WebControls.Repeater.DataBind() +105 System.Web.UI.WebControls.Repeater.EnsureDataBound() +49 System.Web.UI.WebControls.Repeater.OnPreRender(EventArgs e) +15 System.Web.UI.Control.PreRenderRecursiveInternal() +83 System.Web.UI.Control.PreRenderRecursiveInternal() +168 System.Web.UI.Control.PreRenderRecursiveInternal() +168 System.Web.UI.Control.PreRenderRecursiveInternal() +168 System.Web.UI.Control.PreRenderRecursiveInternal() +168 System.Web.UI.Control.PreRenderRecursiveInternal() +168 System.Web.UI.Control.PreRenderRecursiveInternal() +168 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +974 

Answer 1

我有同样的问题，并意识到我使用了错误类型的SqlFunctions。 确保引用了正确的命名空间：

 using System.Data.Entity.SqlServer; 

并不是：

 using System.Data.Objects.SqlClient; 

Answer 2

您不必将其转换为string ，字符串连接将处理该问题。

 AnncTitle = n.AnncTitle + " ", 

您也不必调用ToString 。